VALGRIND(1) valgrind VALGRIND(1)
NAME
valgrind - a suite of tools for debugging and profiling programs
SYNOPSIS
valgrind [valgrind-options] [your-program] [your-program-options]
DESCRIPTION
Valgrind is a flexible program for debugging and profiling Linux
executables. It consists of a core, which provides a synthetic CPU in
software, and a series of debugging and profiling tools. The
architecture is modular, so that new tools can be created easily and
without disturbing the existing structure.
Some of the options described below work with all Valgrind tools, and
some only work with a few or one. The section MEMCHECK OPTIONS and
those below it describe tool-specific options.
This manual page covers only basic usage and options. For more
comprehensive information, please see the HTML documentation on your
system: $INSTALL/share/doc/valgrind/html/index.html, or online:
http://www.valgrind.org/docs/manual/index.html.
TOOL SELECTION OPTIONS
The single most important option.
--tool=<toolname> [default: memcheck]
Run the Valgrind tool called toolname, e.g. memcheck, cachegrind,
callgrind, helgrind, drd, massif, dhat, lackey, none, exp-bbv, etc.
BASIC OPTIONS
These options work with all tools.
-h --help
Show help for all options, both for the core and for the selected
tool. If the option is repeated it is equivalent to giving
--help-debug.
--help-debug
Same as --help, but also lists debugging options which usually are
only of use to Valgrind's developers.
--version
Show the version number of the Valgrind core. Tools can have their
own version numbers. There is a scheme in place to ensure that
tools only execute when the core version is one they are known to
work with. This was done to minimise the chances of strange
problems arising from tool-vs-core version incompatibilities.
-q, --quiet
Run silently, and only print error messages. Useful if you are
running regression tests or have some other automated test
machinery.
-v, --verbose
Be more verbose. Gives extra information on various aspects of your
program, such as: the shared objects loaded, the suppressions used,
the progress of the instrumentation and execution engines, and
warnings about unusual behaviour. Repeating the option increases
the verbosity level.
--trace-children=<yes|no> [default: no]
When enabled, Valgrind will trace into sub-processes initiated via
the exec system call. This is necessary for multi-process programs.
Note that Valgrind does trace into the child of a fork (it would be
difficult not to, since fork makes an identical copy of a process),
so this option is arguably badly named. However, most children of
fork calls immediately call exec anyway.
--trace-children-skip=patt1,patt2,...
This option only has an effect when --trace-children=yes is
specified. It allows for some children to be skipped. The option
takes a comma separated list of patterns for the names of child
executables that Valgrind should not trace into. Patterns may
include the metacharacters ? and *, which have the usual meaning.
This can be useful for pruning uninteresting branches from a tree
of processes being run on Valgrind. But you should be careful when
using it. When Valgrind skips tracing into an executable, it
doesn't just skip tracing that executable, it also skips tracing
any of that executable's child processes. In other words, the flag
doesn't merely cause tracing to stop at the specified executables
-- it skips tracing of entire process subtrees rooted at any of the
specified executables.
--trace-children-skip-by-arg=patt1,patt2,...
This is the same as --trace-children-skip, with one difference: the
decision as to whether to trace into a child process is made by
examining the arguments to the child process, rather than the name
of its executable.
--child-silent-after-fork=<yes|no> [default: no]
When enabled, Valgrind will not show any debugging or logging
output for the child process resulting from a fork call. This can
make the output less confusing (although more misleading) when
dealing with processes that create children. It is particularly
useful in conjunction with --trace-children=. Use of this option is
also strongly recommended if you are requesting XML output
(--xml=yes), since otherwise the XML from child and parent may
become mixed up, which usually makes it useless.
--vgdb=<no|yes|full> [default: yes]
Valgrind will provide "gdbserver" functionality when --vgdb=yes or
--vgdb=full is specified. This allows an external GNU GDB debugger
to control and debug your program when it runs on Valgrind.
--vgdb=full incurs significant performance overheads, but provides
more precise breakpoints and watchpoints. See Debugging your
program using Valgrind's gdbserver and GDB for a detailed
description.
If the embedded gdbserver is enabled but no gdb is currently being
used, the vgdb command line utility can send "monitor commands" to
Valgrind from a shell. The Valgrind core provides a set of Valgrind
monitor commands. A tool can optionally provide tool specific
monitor commands, which are documented in the tool specific
chapter.
--vgdb-error=<number> [default: 999999999]
Use this option when the Valgrind gdbserver is enabled with
--vgdb=yes or --vgdb=full. Tools that report errors will wait for
"number" errors to be reported before freezing the program and
waiting for you to connect with GDB. It follows that a value of
zero will cause the gdbserver to be started before your program is
executed. This is typically used to insert GDB breakpoints before
execution, and also works with tools that do not report errors,
such as Massif.
--vgdb-stop-at=<set> [default: none]
Use this option when the Valgrind gdbserver is enabled with
--vgdb=yes or --vgdb=full. The Valgrind gdbserver will be invoked
for each error after --vgdb-error have been reported. You can
additionally ask the Valgrind gdbserver to be invoked for other
events, specified in one of the following ways:
o a comma separated list of one or more of startup exit
valgrindabexit.
The values startup exit valgrindabexit respectively indicate to
invoke gdbserver before your program is executed, after the
last instruction of your program, on Valgrind abnormal exit
(e.g. internal error, out of memory, ...).
Note: startup and --vgdb-error=0 will both cause Valgrind
gdbserver to be invoked before your program is executed. The
--vgdb-error=0 will in addition cause your program to stop on
all subsequent errors.
o all to specify the complete set. It is equivalent to
--vgdb-stop-at=startup,exit,valgrindabexit.
o none for the empty set.
--track-fds=<yes|no> [default: no]
When enabled, Valgrind will print out a list of open file
descriptors on exit or on request, via the gdbserver monitor
command v.info open_fds. Along with each file descriptor is printed
a stack backtrace of where the file was opened and any details
relating to the file descriptor such as the file name or socket
details.
--time-stamp=<yes|no> [default: no]
When enabled, each message is preceded with an indication of the
elapsed wallclock time since startup, expressed as days, hours,
minutes, seconds and milliseconds.
--log-fd=<number> [default: 2, stderr]
Specifies that Valgrind should send all of its messages to the
specified file descriptor. The default, 2, is the standard error
channel (stderr). Note that this may interfere with the client's
own use of stderr, as Valgrind's output will be interleaved with
any output that the client sends to stderr.
--log-file=<filename>
Specifies that Valgrind should send all of its messages to the
specified file. If the file name is empty, it causes an abort.
There are three special format specifiers that can be used in the
file name.
%p is replaced with the current process ID. This is very useful for
program that invoke multiple processes. WARNING: If you use
--trace-children=yes and your program invokes multiple processes OR
your program forks without calling exec afterwards, and you don't
use this specifier (or the %q specifier below), the Valgrind output
from all those processes will go into one file, possibly jumbled
up, and possibly incomplete. Note: If the program forks and calls
exec afterwards, Valgrind output of the child from the period
between fork and exec will be lost. Fortunately this gap is really
tiny for most programs; and modern programs use posix_spawn anyway.
%n is replaced with a file sequence number unique for this process.
This is useful for processes that produces several files from the
same filename template.
%q{FOO} is replaced with the contents of the environment variable
FOO. If the {FOO} part is malformed, it causes an abort. This
specifier is rarely needed, but very useful in certain
circumstances (eg. when running MPI programs). The idea is that you
specify a variable which will be set differently for each process
in the job, for example BPROC_RANK or whatever is applicable in
your MPI setup. If the named environment variable is not set, it
causes an abort. Note that in some shells, the { and } characters
may need to be escaped with a backslash.
%% is replaced with %.
If an % is followed by any other character, it causes an abort.
If the file name specifies a relative file name, it is put in the
program's initial working directory: this is the current directory
when the program started its execution after the fork or after the
exec. If it specifies an absolute file name (ie. starts with '/')
then it is put there.
--log-socket=<ip-address:port-number>
Specifies that Valgrind should send all of its messages to the
specified port at the specified IP address. The port may be
omitted, in which case port 1500 is used. If a connection cannot be
made to the specified socket, Valgrind falls back to writing output
to the standard error (stderr). This option is intended to be used
in conjunction with the valgrind-listener program. For further
details, see the commentary in the manual.
ERROR-RELATED OPTIONS
These options are used by all tools that can report errors, e.g.
Memcheck, but not Cachegrind.
--xml=<yes|no> [default: no]
When enabled, the important parts of the output (e.g. tool error
messages) will be in XML format rather than plain text.
Furthermore, the XML output will be sent to a different output
channel than the plain text output. Therefore, you also must use
one of --xml-fd, --xml-file or --xml-socket to specify where the
XML is to be sent.
Less important messages will still be printed in plain text, but
because the XML output and plain text output are sent to different
output channels (the destination of the plain text output is still
controlled by --log-fd, --log-file and --log-socket) this should
not cause problems.
This option is aimed at making life easier for tools that consume
Valgrind's output as input, such as GUI front ends. Currently this
option works with Memcheck, Helgrind and DRD. The output format is
specified in the file docs/internals/xml-output-protocol4.txt in
the source tree for Valgrind 3.5.0 or later.
The recommended options for a GUI to pass, when requesting XML
output, are: --xml=yes to enable XML output, --xml-file to send the
XML output to a (presumably GUI-selected) file, --log-file to send
the plain text output to a second GUI-selected file,
--child-silent-after-fork=yes, and -q to restrict the plain text
output to critical error messages created by Valgrind itself. For
example, failure to read a specified suppressions file counts as a
critical error message. In this way, for a successful run the text
output file will be empty. But if it isn't empty, then it will
contain important information which the GUI user should be made
aware of.
--xml-fd=<number> [default: -1, disabled]
Specifies that Valgrind should send its XML output to the specified
file descriptor. It must be used in conjunction with --xml=yes.
--xml-file=<filename>
Specifies that Valgrind should send its XML output to the specified
file. It must be used in conjunction with --xml=yes. Any %p or %q
sequences appearing in the filename are expanded in exactly the
same way as they are for --log-file. See the description of --log-
file for details.
--xml-socket=<ip-address:port-number>
Specifies that Valgrind should send its XML output the specified
port at the specified IP address. It must be used in conjunction
with --xml=yes. The form of the argument is the same as that used
by --log-socket. See the description of --log-socket for further
details.
--xml-user-comment=<string>
Embeds an extra user comment string at the start of the XML output.
Only works when --xml=yes is specified; ignored otherwise.
--demangle=<yes|no> [default: yes]
Enable/disable automatic demangling (decoding) of C++ names.
Enabled by default. When enabled, Valgrind will attempt to
translate encoded C++ names back to something approaching the
original. The demangler handles symbols mangled by g++ versions
2.X, 3.X and 4.X.
An important fact about demangling is that function names mentioned
in suppressions files should be in their mangled form. Valgrind
does not demangle function names when searching for applicable
suppressions, because to do otherwise would make suppression file
contents dependent on the state of Valgrind's demangling machinery,
and also slow down suppression matching.
--num-callers=<number> [default: 12]
Specifies the maximum number of entries shown in stack traces that
identify program locations. Note that errors are commoned up using
only the top four function locations (the place in the current
function, and that of its three immediate callers). So this doesn't
affect the total number of errors reported.
The maximum value for this is 500. Note that higher settings will
make Valgrind run a bit more slowly and take a bit more memory, but
can be useful when working with programs with deeply-nested call
chains.
--unw-stack-scan-thresh=<number> [default: 0] ,
--unw-stack-scan-frames=<number> [default: 5]
Stack-scanning support is available only on ARM targets.
These flags enable and control stack unwinding by stack scanning.
When the normal stack unwinding mechanisms -- usage of Dwarf CFI
records, and frame-pointer following -- fail, stack scanning may be
able to recover a stack trace.
Note that stack scanning is an imprecise, heuristic mechanism that
may give very misleading results, or none at all. It should be used
only in emergencies, when normal unwinding fails, and it is
important to nevertheless have stack traces.
Stack scanning is a simple technique: the unwinder reads words from
the stack, and tries to guess which of them might be return
addresses, by checking to see if they point just after ARM or Thumb
call instructions. If so, the word is added to the backtrace.
The main danger occurs when a function call returns, leaving its
return address exposed, and a new function is called, but the new
function does not overwrite the old address. The result of this is
that the backtrace may contain entries for functions which have
already returned, and so be very confusing.
A second limitation of this implementation is that it will scan
only the page (4KB, normally) containing the starting stack
pointer. If the stack frames are large, this may result in only a
few (or not even any) being present in the trace. Also, if you are
unlucky and have an initial stack pointer near the end of its
containing page, the scan may miss all interesting frames.
By default stack scanning is disabled. The normal use case is to
ask for it when a stack trace would otherwise be very short. So, to
enable it, use --unw-stack-scan-thresh=number. This requests
Valgrind to try using stack scanning to "extend" stack traces which
contain fewer than number frames.
If stack scanning does take place, it will only generate at most
the number of frames specified by --unw-stack-scan-frames.
Typically, stack scanning generates so many garbage entries that
this value is set to a low value (5) by default. In no case will a
stack trace larger than the value specified by --num-callers be
created.
--error-limit=<yes|no> [default: yes]
When enabled, Valgrind stops reporting errors after 10,000,000 in
total, or 1,000 different ones, have been seen. This is to stop the
error tracking machinery from becoming a huge performance overhead
in programs with many errors.
--error-exitcode=<number> [default: 0]
Specifies an alternative exit code to return if Valgrind reported
any errors in the run. When set to the default value (zero), the
return value from Valgrind will always be the return value of the
process being simulated. When set to a nonzero value, that value is
returned instead, if Valgrind detects any errors. This is useful
for using Valgrind as part of an automated test suite, since it
makes it easy to detect test cases for which Valgrind has reported
errors, just by inspecting return codes.
--exit-on-first-error=<yes|no> [default: no]
If this option is enabled, Valgrind exits on the first error. A
nonzero exit value must be defined using --error-exitcode option.
Useful if you are running regression tests or have some other
automated test machinery.
--error-markers=<begin>,<end> [default: none]
When errors are output as plain text (i.e. XML not used),
--error-markers instructs to output a line containing the begin
(end) string before (after) each error.
Such marker lines facilitate searching for errors and/or extracting
errors in an output file that contain valgrind errors mixed with
the program output.
Note that empty markers are accepted. So, only using a begin (or an
end) marker is possible.
--show-error-list=no|yes [default: no]
If this option is enabled, for tools that report errors, valgrind
will show the list of detected errors and the list of used
suppressions at exit.
Note that at verbosity 2 and above, valgrind automatically shows
the list of detected errors and the list of used suppressions at
exit, unless --show-error-list=no is selected.
-s
Specifying -s is equivalent to --show-error-list=yes.
--sigill-diagnostics=<yes|no> [default: yes]
Enable/disable printing of illegal instruction diagnostics. Enabled
by default, but defaults to disabled when --quiet is given. The
default can always be explicitly overridden by giving this option.
When enabled, a warning message will be printed, along with some
diagnostics, whenever an instruction is encountered that Valgrind
cannot decode or translate, before the program is given a SIGILL
signal. Often an illegal instruction indicates a bug in the program
or missing support for the particular instruction in Valgrind. But
some programs do deliberately try to execute an instruction that
might be missing and trap the SIGILL signal to detect processor
features. Using this flag makes it possible to avoid the diagnostic
output that you would otherwise get in such cases.
--keep-debuginfo=<yes|no> [default: no]
When enabled, keep ("archive") symbols and all other debuginfo for
unloaded code. This allows saved stack traces to include file/line
info for code that has been dlclose'd (or similar). Be careful with
this, since it can lead to unbounded memory use for programs which
repeatedly load and unload shared objects.
Some tools and some functionalities have only limited support for
archived debug info. Memcheck fully supports it. Generally, tools
that report errors can use archived debug info to show the error
stack traces. The known limitations are: Helgrind's past access
stack trace of a race condition is does not use archived debug
info. Massif (and more generally the xtree Massif output format)
does not make use of archived debug info. Only Memcheck has been
(somewhat) tested with --keep-debuginfo=yes, so other tools may
have unknown limitations.
--show-below-main=<yes|no> [default: no]
By default, stack traces for errors do not show any functions that
appear beneath main because most of the time it's uninteresting C
library stuff and/or gobbledygook. Alternatively, if main is not
present in the stack trace, stack traces will not show any
functions below main-like functions such as glibc's
__libc_start_main. Furthermore, if main-like functions are present
in the trace, they are normalised as (below main), in order to make
the output more deterministic.
If this option is enabled, all stack trace entries will be shown
and main-like functions will not be normalised.
--fullpath-after=<string> [default: don't show source paths]
By default Valgrind only shows the filenames in stack traces, but
not full paths to source files. When using Valgrind in large
projects where the sources reside in multiple different
directories, this can be inconvenient. --fullpath-after provides a
flexible solution to this problem. When this option is present, the
path to each source file is shown, with the following all-important
caveat: if string is found in the path, then the path up to and
including string is omitted, else the path is shown unmodified.
Note that string is not required to be a prefix of the path.
For example, consider a file named
/home/janedoe/blah/src/foo/bar/xyzzy.c. Specifying
--fullpath-after=/home/janedoe/blah/src/ will cause Valgrind to
show the name as foo/bar/xyzzy.c.
Because the string is not required to be a prefix,
--fullpath-after=src/ will produce the same output. This is useful
when the path contains arbitrary machine-generated characters. For
example, the path /my/build/dir/C32A1B47/blah/src/foo/xyzzy can be
pruned to foo/xyzzy using --fullpath-after=/blah/src/.
If you simply want to see the full path, just specify an empty
string: --fullpath-after=. This isn't a special case, merely a
logical consequence of the above rules.
Finally, you can use --fullpath-after multiple times. Any
appearance of it causes Valgrind to switch to producing full paths
and applying the above filtering rule. Each produced path is
compared against all the --fullpath-after-specified strings, in the
order specified. The first string to match causes the path to be
truncated as described above. If none match, the full path is
shown. This facilitates chopping off prefixes when the sources are
drawn from a number of unrelated directories.
--extra-debuginfo-path=<path> [default: undefined and unused]
By default Valgrind searches in several well-known paths for debug
objects, such as /usr/lib/debug/.
However, there may be scenarios where you may wish to put debug
objects at an arbitrary location, such as external storage when
running Valgrind on a mobile device with limited local storage.
Another example might be a situation where you do not have
permission to install debug object packages on the system where you
are running Valgrind.
In these scenarios, you may provide an absolute path as an extra,
final place for Valgrind to search for debug objects by specifying
--extra-debuginfo-path=/path/to/debug/objects. The given path will
be prepended to the absolute path name of the searched-for object.
For example, if Valgrind is looking for the debuginfo for
/w/x/y/zz.so and --extra-debuginfo-path=/a/b/c is specified, it
will look for a debug object at /a/b/c/w/x/y/zz.so.
This flag should only be specified once. If it is specified
multiple times, only the last instance is honoured.
--debuginfo-server=ipaddr:port [default: undefined and unused]
This is a new, experimental, feature introduced in version 3.9.0.
In some scenarios it may be convenient to read debuginfo from
objects stored on a different machine. With this flag, Valgrind
will query a debuginfo server running on ipaddr and listening on
port port, if it cannot find the debuginfo object in the local
filesystem.
The debuginfo server must accept TCP connections on port port. The
debuginfo server is contained in the source file
auxprogs/valgrind-di-server.c. It will only serve from the
directory it is started in. port defaults to 1500 in both client
and server if not specified.
If Valgrind looks for the debuginfo for /w/x/y/zz.so by using the
debuginfo server, it will strip the pathname components and merely
request zz.so on the server. That in turn will look only in its
current working directory for a matching debuginfo object.
The debuginfo data is transmitted in small fragments (8 KB) as
requested by Valgrind. Each block is compressed using LZO to reduce
transmission time. The implementation has been tuned for best
performance over a single-stage 802.11g (WiFi) network link.
Note that checks for matching primary vs debug objects, using GNU
debuglink CRC scheme, are performed even when using the debuginfo
server. To disable such checking, you need to also specify
--allow-mismatched-debuginfo=yes.
By default the Valgrind build system will build valgrind-di-server
for the target platform, which is almost certainly not what you
want. So far we have been unable to find out how to get
automake/autoconf to build it for the build platform. If you want
to use it, you will have to recompile it by hand using the command
shown at the top of auxprogs/valgrind-di-server.c.
--allow-mismatched-debuginfo=no|yes [no]
When reading debuginfo from separate debuginfo objects, Valgrind
will by default check that the main and debuginfo objects match,
using the GNU debuglink mechanism. This guarantees that it does not
read debuginfo from out of date debuginfo objects, and also ensures
that Valgrind can't crash as a result of mismatches.
This check can be overridden using
--allow-mismatched-debuginfo=yes. This may be useful when the
debuginfo and main objects have not been split in the proper way.
Be careful when using this, though: it disables all consistency
checking, and Valgrind has been observed to crash when the main and
debuginfo objects don't match.
--suppressions=<filename> [default: $PREFIX/lib/valgrind/default.supp]
Specifies an extra file from which to read descriptions of errors
to suppress. You may use up to 100 extra suppression files.
--gen-suppressions=<yes|no|all> [default: no]
When set to yes, Valgrind will pause after every error shown and
print the line:
---- Print suppression ? --- [Return/N/n/Y/y/C/c] ----
Pressing Ret, or N Ret or n Ret, causes Valgrind continue execution
without printing a suppression for this error.
Pressing Y Ret or y Ret causes Valgrind to write a suppression for
this error. You can then cut and paste it into a suppression file
if you don't want to hear about the error in the future.
When set to all, Valgrind will print a suppression for every
reported error, without querying the user.
This option is particularly useful with C++ programs, as it prints
out the suppressions with mangled names, as required.
Note that the suppressions printed are as specific as possible. You
may want to common up similar ones, by adding wildcards to function
names, and by using frame-level wildcards. The wildcarding
facilities are powerful yet flexible, and with a bit of careful
editing, you may be able to suppress a whole family of related
errors with only a few suppressions.
Sometimes two different errors are suppressed by the same
suppression, in which case Valgrind will output the suppression
more than once, but you only need to have one copy in your
suppression file (but having more than one won't cause problems).
Also, the suppression name is given as <insert a suppression name
here>; the name doesn't really matter, it's only used with the -v
option which prints out all used suppression records.
--input-fd=<number> [default: 0, stdin]
When using --gen-suppressions=yes, Valgrind will stop so as to read
keyboard input from you when each error occurs. By default it reads
from the standard input (stdin), which is problematic for programs
which close stdin. This option allows you to specify an alternative
file descriptor from which to read input.
--dsymutil=no|yes [yes]
This option is only relevant when running Valgrind on Mac OS X.
Mac OS X uses a deferred debug information (debuginfo) linking
scheme. When object files containing debuginfo are linked into a
.dylib or an executable, the debuginfo is not copied into the final
file. Instead, the debuginfo must be linked manually by running
dsymutil, a system-provided utility, on the executable or .dylib.
The resulting combined debuginfo is placed in a directory alongside
the executable or .dylib, but with the extension .dSYM.
With --dsymutil=no, Valgrind will detect cases where the .dSYM
directory is either missing, or is present but does not appear to
match the associated executable or .dylib, most likely because it
is out of date. In these cases, Valgrind will print a warning
message but take no further action.
With --dsymutil=yes, Valgrind will, in such cases, automatically
run dsymutil as necessary to bring the debuginfo up to date. For
all practical purposes, if you always use --dsymutil=yes, then
there is never any need to run dsymutil manually or as part of your
applications's build system, since Valgrind will run it as
necessary.
Valgrind will not attempt to run dsymutil on any executable or
library in /usr/, /bin/, /sbin/, /opt/, /sw/, /System/, /Library/
or /Applications/ since dsymutil will always fail in such
situations. It fails both because the debuginfo for such
pre-installed system components is not available anywhere, and also
because it would require write privileges in those directories.
Be careful when using --dsymutil=yes, since it will cause
pre-existing .dSYM directories to be silently deleted and
re-created. Also note that dsymutil is quite slow, sometimes
excessively so.
--max-stackframe=<number> [default: 2000000]
The maximum size of a stack frame. If the stack pointer moves by
more than this amount then Valgrind will assume that the program is
switching to a different stack.
You may need to use this option if your program has large
stack-allocated arrays. Valgrind keeps track of your program's
stack pointer. If it changes by more than the threshold amount,
Valgrind assumes your program is switching to a different stack,
and Memcheck behaves differently than it would for a stack pointer
change smaller than the threshold. Usually this heuristic works
well. However, if your program allocates large structures on the
stack, this heuristic will be fooled, and Memcheck will
subsequently report large numbers of invalid stack accesses. This
option allows you to change the threshold to a different value.
You should only consider use of this option if Valgrind's debug
output directs you to do so. In that case it will tell you the new
threshold you should specify.
In general, allocating large structures on the stack is a bad idea,
because you can easily run out of stack space, especially on
systems with limited memory or which expect to support large
numbers of threads each with a small stack, and also because the
error checking performed by Memcheck is more effective for
heap-allocated data than for stack-allocated data. If you have to
use this option, you may wish to consider rewriting your code to
allocate on the heap rather than on the stack.
--main-stacksize=<number> [default: use current 'ulimit' value]
Specifies the size of the main thread's stack.
To simplify its memory management, Valgrind reserves all required
space for the main thread's stack at startup. That means it needs
to know the required stack size at startup.
By default, Valgrind uses the current "ulimit" value for the stack
size, or 16 MB, whichever is lower. In many cases this gives a
stack size in the range 8 to 16 MB, which almost never overflows
for most applications.
If you need a larger total stack size, use --main-stacksize to
specify it. Only set it as high as you need, since reserving far
more space than you need (that is, hundreds of megabytes more than
you need) constrains Valgrind's memory allocators and may reduce
the total amount of memory that Valgrind can use. This is only
really of significance on 32-bit machines.
On Linux, you may request a stack of size up to 2GB. Valgrind will
stop with a diagnostic message if the stack cannot be allocated.
--main-stacksize only affects the stack size for the program's
initial thread. It has no bearing on the size of thread stacks, as
Valgrind does not allocate those.
You may need to use both --main-stacksize and --max-stackframe
together. It is important to understand that --main-stacksize sets
the maximum total stack size, whilst --max-stackframe specifies the
largest size of any one stack frame. You will have to work out the
--main-stacksize value for yourself (usually, if your applications
segfaults). But Valgrind will tell you the needed --max-stackframe
size, if necessary.
As discussed further in the description of --max-stackframe, a
requirement for a large stack is a sign of potential portability
problems. You are best advised to place all large data in
heap-allocated memory.
--max-threads=<number> [default: 500]
By default, Valgrind can handle to up to 500 threads. Occasionally,
that number is too small. Use this option to provide a different
limit. E.g. --max-threads=3000.
MALLOC()-RELATED OPTIONS
For tools that use their own version of malloc (e.g. Memcheck, Massif,
Helgrind, DRD), the following options apply.
--alignment=<number> [default: 8 or 16, depending on the platform]
By default Valgrind's malloc, realloc, etc, return a block whose
starting address is 8-byte aligned or 16-byte aligned (the value
depends on the platform and matches the platform default). This
option allows you to specify a different alignment. The supplied
value must be greater than or equal to the default, less than or
equal to 4096, and must be a power of two.
--redzone-size=<number> [default: depends on the tool]
Valgrind's malloc, realloc, etc, add padding blocks before and
after each heap block allocated by the program being run. Such
padding blocks are called redzones. The default value for the
redzone size depends on the tool. For example, Memcheck adds and
protects a minimum of 16 bytes before and after each block
allocated by the client. This allows it to detect block underruns
or overruns of up to 16 bytes.
Increasing the redzone size makes it possible to detect overruns of
larger distances, but increases the amount of memory used by
Valgrind. Decreasing the redzone size will reduce the memory needed
by Valgrind but also reduces the chances of detecting
over/underruns, so is not recommended.
--xtree-memory=none|allocs|full [none]
Tools replacing Valgrind's malloc, realloc, etc, can optionally
produce an execution tree detailing which piece of code is
responsible for heap memory usage. See Execution Trees for a
detailed explanation about execution trees.
When set to none, no memory execution tree is produced.
When set to allocs, the memory execution tree gives the current
number of allocated bytes and the current number of allocated
blocks.
When set to full, the memory execution tree gives 6 different
measurements : the current number of allocated bytes and blocks
(same values as for allocs), the total number of allocated bytes
and blocks, the total number of freed bytes and blocks.
Note that the overhead in cpu and memory to produce an xtree
depends on the tool. The overhead in cpu is small for the value
allocs, as the information needed to produce this report is
maintained in any case by the tool. For massif and helgrind,
specifying full implies to capture a stack trace for each free
operation, while normally these tools only capture an allocation
stack trace. For Memcheck, the cpu overhead for the value full is
small, as this can only be used in combination with
--keep-stacktraces=alloc-and-free or
--keep-stacktraces=alloc-then-free, which already records a stack
trace for each free operation. The memory overhead varies between 5
and 10 words per unique stacktrace in the xtree, plus the memory
needed to record the stack trace for the free operations, if needed
specifically for the xtree.
--xtree-memory-file=<filename> [default: xtmemory.kcg.%p]
Specifies that Valgrind should produce the xtree memory report in
the specified file. Any %p or %q sequences appearing in the
filename are expanded in exactly the same way as they are for
--log-file. See the description of --log-file for details.
If the filename contains the extension .ms, then the produced file
format will be a massif output file format. If the filename
contains the extension .kcg or no extension is provided or
recognised, then the produced file format will be a callgrind
output format.
See Execution Trees for a detailed explanation about execution
trees formats.
UNCOMMON OPTIONS
These options apply to all tools, as they affect certain obscure
workings of the Valgrind core. Most people won't need to use them.
--smc-check=<none|stack|all|all-non-file> [default: all-non-file for
x86/amd64/s390x, stack for other archs]
This option controls Valgrind's detection of self-modifying code.
If no checking is done, when a program executes some code, then
overwrites it with new code, and executes the new code, Valgrind
will continue to execute the translations it made for the old code.
This will likely lead to incorrect behaviour and/or crashes.
For "modern" architectures -- anything that's not x86, amd64 or
s390x -- the default is stack. This is because a correct program
must take explicit action to reestablish D-I cache coherence
following code modification. Valgrind observes and honours such
actions, with the result that self-modifying code is transparently
handled with zero extra cost.
For x86, amd64 and s390x, the program is not required to notify the
hardware of required D-I coherence syncing. Hence the default is
all-non-file, which covers the normal case of generating code into
an anonymous (non-file-backed) mmap'd area.
The meanings of the four available settings are as follows. No
detection (none), detect self-modifying code on the stack (which is
used by GCC to implement nested functions) (stack), detect
self-modifying code everywhere (all), and detect self-modifying
code everywhere except in file-backed mappings (all-non-file).
Running with all will slow Valgrind down noticeably. Running with
none will rarely speed things up, since very little code gets
dynamically generated in most programs. The
VALGRIND_DISCARD_TRANSLATIONS client request is an alternative to
--smc-check=all and --smc-check=all-non-file that requires more
programmer effort but allows Valgrind to run your program faster,
by telling it precisely when translations need to be re-made.
--smc-check=all-non-file provides a cheaper but more limited
version of --smc-check=all. It adds checks to any translations that
do not originate from file-backed memory mappings. Typical
applications that generate code, for example JITs in web browsers,
generate code into anonymous mmaped areas, whereas the "fixed" code
of the browser always lives in file-backed mappings.
--smc-check=all-non-file takes advantage of this observation,
limiting the overhead of checking to code which is likely to be JIT
generated.
--read-inline-info=<yes|no> [default: see below]
When enabled, Valgrind will read information about inlined function
calls from DWARF3 debug info. This slows Valgrind startup and makes
it use more memory (typically for each inlined piece of code, 6
words and space for the function name), but it results in more
descriptive stacktraces. Currently, this functionality is enabled
by default only for Linux, Android and Solaris targets and only for
the tools Memcheck, Massif, Helgrind and DRD. Here is an example of
some stacktraces with --read-inline-info=no:
==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x80484EA: main (inlinfo.c:6)
==15380==
==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x8048550: fun_noninline (inlinfo.c:6)
==15380== by 0x804850E: main (inlinfo.c:34)
==15380==
==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x8048520: main (inlinfo.c:6)
And here are the same errors with --read-inline-info=yes:
==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x80484EA: fun_d (inlinfo.c:6)
==15377== by 0x80484EA: fun_c (inlinfo.c:14)
==15377== by 0x80484EA: fun_b (inlinfo.c:20)
==15377== by 0x80484EA: fun_a (inlinfo.c:26)
==15377== by 0x80484EA: main (inlinfo.c:33)
==15377==
==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x8048550: fun_d (inlinfo.c:6)
==15377== by 0x8048550: fun_noninline (inlinfo.c:41)
==15377== by 0x804850E: main (inlinfo.c:34)
==15377==
==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x8048520: fun_d (inlinfo.c:6)
==15377== by 0x8048520: main (inlinfo.c:35)
--read-var-info=<yes|no> [default: no]
When enabled, Valgrind will read information about variable types
and locations from DWARF3 debug info. This slows Valgrind startup
significantly and makes it use significantly more memory, but for
the tools that can take advantage of it (Memcheck, Helgrind, DRD)
it can result in more precise error messages. For example, here are
some standard errors issued by Memcheck:
==15363== Uninitialised byte(s) found during client check request
==15363== at 0x80484A9: croak (varinfo1.c:28)
==15363== by 0x8048544: main (varinfo1.c:55)
==15363== Address 0x80497f7 is 7 bytes inside data symbol "global_i2"
==15363==
==15363== Uninitialised byte(s) found during client check request
==15363== at 0x80484A9: croak (varinfo1.c:28)
==15363== by 0x8048550: main (varinfo1.c:56)
==15363== Address 0xbea0d0cc is on thread 1's stack
==15363== in frame #1, created by main (varinfo1.c:45)
And here are the same errors with --read-var-info=yes:
==15370== Uninitialised byte(s) found during client check request
==15370== at 0x80484A9: croak (varinfo1.c:28)
==15370== by 0x8048544: main (varinfo1.c:55)
==15370== Location 0x80497f7 is 0 bytes inside global_i2[7],
==15370== a global variable declared at varinfo1.c:41
==15370==
==15370== Uninitialised byte(s) found during client check request
==15370== at 0x80484A9: croak (varinfo1.c:28)
==15370== by 0x8048550: main (varinfo1.c:56)
==15370== Location 0xbeb4a0cc is 0 bytes inside local var "local"
==15370== declared at varinfo1.c:46, in frame #1 of thread 1
--vgdb-poll=<number> [default: 5000]
As part of its main loop, the Valgrind scheduler will poll to check
if some activity (such as an external command or some input from a
gdb) has to be handled by gdbserver. This activity poll will be
done after having run the given number of basic blocks (or slightly
more than the given number of basic blocks). This poll is quite
cheap so the default value is set relatively low. You might further
decrease this value if vgdb cannot use ptrace system call to
interrupt Valgrind if all threads are (most of the time) blocked in
a system call.
--vgdb-shadow-registers=no|yes [default: no]
When activated, gdbserver will expose the Valgrind shadow registers
to GDB. With this, the value of the Valgrind shadow registers can
be examined or changed using GDB. Exposing shadow registers only
works with GDB version 7.1 or later.
--vgdb-prefix=<prefix> [default: /tmp/vgdb-pipe]
To communicate with gdb/vgdb, the Valgrind gdbserver creates 3
files (2 named FIFOs and a mmap shared memory file). The prefix
option controls the directory and prefix for the creation of these
files.
--run-libc-freeres=<yes|no> [default: yes]
This option is only relevant when running Valgrind on Linux.
The GNU C library (libc.so), which is used by all programs, may
allocate memory for its own uses. Usually it doesn't bother to free
that memory when the program ends--there would be no point, since
the Linux kernel reclaims all process resources when a process
exits anyway, so it would just slow things down.
The glibc authors realised that this behaviour causes leak
checkers, such as Valgrind, to falsely report leaks in glibc, when
a leak check is done at exit. In order to avoid this, they provided
a routine called __libc_freeres specifically to make glibc release
all memory it has allocated. Memcheck therefore tries to run
__libc_freeres at exit.
Unfortunately, in some very old versions of glibc, __libc_freeres
is sufficiently buggy to cause segmentation faults. This was
particularly noticeable on Red Hat 7.1. So this option is provided
in order to inhibit the run of __libc_freeres. If your program
seems to run fine on Valgrind, but segfaults at exit, you may find
that --run-libc-freeres=no fixes that, although at the cost of
possibly falsely reporting space leaks in libc.so.
--run-cxx-freeres=<yes|no> [default: yes]
This option is only relevant when running Valgrind on Linux or
Solaris C++ programs.
The GNU Standard C++ library (libstdc++.so), which is used by all
C++ programs compiled with g++, may allocate memory for its own
uses. Usually it doesn't bother to free that memory when the
program ends--there would be no point, since the kernel reclaims
all process resources when a process exits anyway, so it would just
slow things down.
The gcc authors realised that this behaviour causes leak checkers,
such as Valgrind, to falsely report leaks in libstdc++, when a leak
check is done at exit. In order to avoid this, they provided a
routine called __gnu_cxx::__freeres specifically to make libstdc++
release all memory it has allocated. Memcheck therefore tries to
run __gnu_cxx::__freeres at exit.
For the sake of flexibility and unforeseen problems with
__gnu_cxx::__freeres, option --run-cxx-freeres=no exists, although
at the cost of possibly falsely reporting space leaks in
libstdc++.so.
--sim-hints=hint1,hint2,...
Pass miscellaneous hints to Valgrind which slightly modify the
simulated behaviour in nonstandard or dangerous ways, possibly to
help the simulation of strange features. By default no hints are
enabled. Use with caution! Currently known hints are:
o lax-ioctls: Be very lax about ioctl handling; the only
assumption is that the size is correct. Doesn't require the
full buffer to be initialised when writing. Without this, using
some device drivers with a large number of strange ioctl
commands becomes very tiresome.
o fuse-compatible: Enable special handling for certain system
calls that may block in a FUSE file-system. This may be
necessary when running Valgrind on a multi-threaded program
that uses one thread to manage a FUSE file-system and another
thread to access that file-system.
o enable-outer: Enable some special magic needed when the program
being run is itself Valgrind.
o no-inner-prefix: Disable printing a prefix > in front of each
stdout or stderr output line in an inner Valgrind being run by
an outer Valgrind. This is useful when running Valgrind
regression tests in an outer/inner setup. Note that the prefix
> will always be printed in front of the inner debug logging
lines.
o no-nptl-pthread-stackcache: This hint is only relevant when
running Valgrind on Linux; it is ignored on Solaris and Mac OS
X.
The GNU glibc pthread library (libpthread.so), which is used by
pthread programs, maintains a cache of pthread stacks. When a
pthread terminates, the memory used for the pthread stack and
some thread local storage related data structure are not always
directly released. This memory is kept in a cache (up to a
certain size), and is re-used if a new thread is started.
This cache causes the helgrind tool to report some false
positive race condition errors on this cached memory, as
helgrind does not understand the internal glibc cache
synchronisation primitives. So, when using helgrind, disabling
the cache helps to avoid false positive race conditions, in
particular when using thread local storage variables (e.g.
variables using the __thread qualifier).
When using the memcheck tool, disabling the cache ensures the
memory used by glibc to handle __thread variables is directly
released when a thread terminates.
Note: Valgrind disables the cache using some internal knowledge
of the glibc stack cache implementation and by examining the
debug information of the pthread library. This technique is
thus somewhat fragile and might not work for all glibc
versions. This has been successfully tested with various glibc
versions (e.g. 2.11, 2.16, 2.18) on various platforms.
o lax-doors: (Solaris only) Be very lax about door syscall
handling over unrecognised door file descriptors. Does not
require that full buffer is initialised when writing. Without
this, programs using libdoor(3LIB) functionality with
completely proprietary semantics may report large number of
false positives.
o fallback-llsc: (MIPS and ARM64 only): Enables an alternative
implementation of Load-Linked (LL) and Store-Conditional (SC)
instructions. The standard implementation gives more correct
behaviour, but can cause indefinite looping on certain
processor implementations that are intolerant of extra memory
references between LL and SC. So far this is known only to
happen on Cavium 3 cores. You should not need to use this flag,
since the relevant cores are detected at startup and the
alternative implementation is automatically enabled if
necessary. There is no equivalent anti-flag: you cannot
force-disable the alternative implementation, if it is
automatically enabled. The underlying problem exists because
the "standard" implementation of LL and SC is done by copying
through LL and SC instructions into the instrumented code.
However, tools may insert extra instrumentation memory
references in between the LL and SC instructions. These memory
references are not present in the original uninstrumented code,
and their presence in the instrumented code can cause the SC
instructions to persistently fail, leading to indefinite
looping in LL-SC blocks. The alternative implementation gives
correct behaviour of LL and SC instructions between threads in
a process, up to and including the ABA scenario. It also gives
correct behaviour between a Valgrinded thread and a
non-Valgrinded thread running in a different process, that
communicate via shared memory, but only up to and including
correct CAS behaviour -- in this case the ABA scenario may not
be correctly handled.
--fair-sched=<no|yes|try> [default: no]
The --fair-sched option controls the locking mechanism used by
Valgrind to serialise thread execution. The locking mechanism
controls the way the threads are scheduled, and different settings
give different trade-offs between fairness and performance. For
more details about the Valgrind thread serialisation scheme and its
impact on performance and thread scheduling, see Scheduling and
Multi-Thread Performance.
o The value --fair-sched=yes activates a fair scheduler. In
short, if multiple threads are ready to run, the threads will
be scheduled in a round robin fashion. This mechanism is not
available on all platforms or Linux versions. If not available,
using --fair-sched=yes will cause Valgrind to terminate with an
error.
You may find this setting improves overall responsiveness if
you are running an interactive multithreaded program, for
example a web browser, on Valgrind.
o The value --fair-sched=try activates fair scheduling if
available on the platform. Otherwise, it will automatically
fall back to --fair-sched=no.
o The value --fair-sched=no activates a scheduler which does not
guarantee fairness between threads ready to run, but which in
general gives the highest performance.
--kernel-variant=variant1,variant2,...
Handle system calls and ioctls arising from minor variants of the
default kernel for this platform. This is useful for running on
hacked kernels or with kernel modules which support nonstandard
ioctls, for example. Use with caution. If you don't understand what
this option does then you almost certainly don't need it. Currently
known variants are:
o bproc: support the sys_broc system call on x86. This is for
running on BProc, which is a minor variant of standard Linux
which is sometimes used for building clusters.
o android-no-hw-tls: some versions of the Android emulator for
ARM do not provide a hardware TLS (thread-local state)
register, and Valgrind crashes at startup. Use this variant to
select software support for TLS.
o android-gpu-sgx5xx: use this to support handling of proprietary
ioctls for the PowerVR SGX 5XX series of GPUs on Android
devices. Failure to select this does not cause stability
problems, but may cause Memcheck to report false errors after
the program performs GPU-specific ioctls.
o android-gpu-adreno3xx: similarly, use this to support handling
of proprietary ioctls for the Qualcomm Adreno 3XX series of
GPUs on Android devices.
--merge-recursive-frames=<number> [default: 0]
Some recursive algorithms, for example balanced binary tree
implementations, create many different stack traces, each
containing cycles of calls. A cycle is defined as two identical
program counter values separated by zero or more other program
counter values. Valgrind may then use a lot of memory to store all
these stack traces. This is a poor use of memory considering that
such stack traces contain repeated uninteresting recursive calls
instead of more interesting information such as the function that
has initiated the recursive call.
The option --merge-recursive-frames=<number> instructs Valgrind to
detect and merge recursive call cycles having a size of up to
<number> frames. When such a cycle is detected, Valgrind records
the cycle in the stack trace as a unique program counter.
The value 0 (the default) causes no recursive call merging. A value
of 1 will cause stack traces of simple recursive algorithms (for
example, a factorial implementation) to be collapsed. A value of 2
will usually be needed to collapse stack traces produced by
recursive algorithms such as binary trees, quick sort, etc. Higher
values might be needed for more complex recursive algorithms.
Note: recursive calls are detected by analysis of program counter
values. They are not detected by looking at function names.
--num-transtab-sectors=<number> [default: 6 for Android platforms, 16
for all others]
Valgrind translates and instruments your program's machine code in
small fragments (basic blocks). The translations are stored in a
translation cache that is divided into a number of sections
(sectors). If the cache is full, the sector containing the oldest
translations is emptied and reused. If these old translations are
needed again, Valgrind must re-translate and re-instrument the
corresponding machine code, which is expensive. If the "executed
instructions" working set of a program is big, increasing the
number of sectors may improve performance by reducing the number of
re-translations needed. Sectors are allocated on demand. Once
allocated, a sector can never be freed, and occupies considerable
space, depending on the tool and the value of
--avg-transtab-entry-size (about 40 MB per sector for Memcheck).
Use the option --stats=yes to obtain precise information about the
memory used by a sector and the allocation and recycling of
sectors.
--avg-transtab-entry-size=<number> [default: 0, meaning use tool
provided default]
Average size of translated basic block. This average size is used
to dimension the size of a sector. Each tool provides a default
value to be used. If this default value is too small, the
translation sectors will become full too quickly. If this default
value is too big, a significant part of the translation sector
memory will be unused. Note that the average size of a basic block
translation depends on the tool, and might depend on tool options.
For example, the memcheck option --track-origins=yes increases the
size of the basic block translations. Use --avg-transtab-entry-size
to tune the size of the sectors, either to gain memory or to avoid
too many retranslations.
--aspace-minaddr=<address> [default: depends on the platform]
To avoid potential conflicts with some system libraries, Valgrind
does not use the address space below --aspace-minaddr value,
keeping it reserved in case a library specifically requests memory
in this region. So, some "pessimistic" value is guessed by Valgrind
depending on the platform. On linux, by default, Valgrind avoids
using the first 64MB even if typically there is no conflict in this
complete zone. You can use the option --aspace-minaddr to have your
memory hungry application benefitting from more of this lower
memory. On the other hand, if you encounter a conflict, increasing
aspace-minaddr value might solve it. Conflicts will typically
manifest themselves with mmap failures in the low range of the
address space. The provided address must be page aligned and must
be equal or bigger to 0x1000 (4KB). To find the default value on
your platform, do something such as valgrind -d -d date 2>&1 | grep
-i minaddr. Values lower than 0x10000 (64KB) are known to create
problems on some distributions.
--valgrind-stacksize=<number> [default: 1MB]
For each thread, Valgrind needs its own 'private' stack. The
default size for these stacks is largely dimensioned, and so should
be sufficient in most cases. In case the size is too small,
Valgrind will segfault. Before segfaulting, a warning might be
produced by Valgrind when approaching the limit.
Use the option --valgrind-stacksize if such an (unlikely) warning
is produced, or Valgrind dies due to a segmentation violation. Such
segmentation violations have been seen when demangling huge C++
symbols.
If your application uses many threads and needs a lot of memory,
you can gain some memory by reducing the size of these Valgrind
stacks using the option --valgrind-stacksize.
--show-emwarns=<yes|no> [default: no]
When enabled, Valgrind will emit warnings about its CPU emulation
in certain cases. These are usually not interesting.
--require-text-symbol=:sonamepatt:fnnamepatt
When a shared object whose soname matches sonamepatt is loaded into
the process, examine all the text symbols it exports. If none of
those match fnnamepatt, print an error message and abandon the run.
This makes it possible to ensure that the run does not continue
unless a given shared object contains a particular function name.
Both sonamepatt and fnnamepatt can be written using the usual ?
and * wildcards. For example: ":*libc.so*:foo?bar". You may use
characters other than a colon to separate the two patterns. It is
only important that the first character and the separator character
are the same. For example, the above example could also be written
"Q*libc.so*Qfoo?bar". Multiple
--require-text-symbol flags are allowed, in which case shared
objects that are loaded into the process will be checked against
all of them.
The purpose of this is to support reliable usage of marked-up
libraries. For example, suppose we have a version of GCC's
libgomp.so which has been marked up with annotations to support
Helgrind. It is only too easy and confusing to load the wrong,
un-annotated libgomp.so into the application. So the idea is: add a
text symbol in the marked-up library, for example
annotated_for_helgrind_3_6, and then give the flag
--require-text-symbol=:*libgomp*so*:annotated_for_helgrind_3_6 so
that when libgomp.so is loaded, Valgrind scans its symbol table,
and if the symbol isn't present the run is aborted, rather than
continuing silently with the un-marked-up library. Note that you
should put the entire flag in quotes to stop shells expanding up
the * and ? wildcards.
--soname-synonyms=syn1=pattern1,syn2=pattern2,...
When a shared library is loaded, Valgrind checks for functions in
the library that must be replaced or wrapped. For example, Memcheck
replaces some string and memory functions (strchr, strlen, strcpy,
memchr, memcpy, memmove, etc.) with its own versions. Such
replacements are normally done only in shared libraries whose
soname matches a predefined soname pattern (e.g. libc.so* on
linux). By default, no replacement is done for a statically linked
binary or for alternative libraries, except for the allocation
functions (malloc, free, calloc, memalign, realloc, operator new,
operator delete, etc.) Such allocation functions are intercepted by
default in any shared library or in the executable if they are
exported as global symbols. This means that if a replacement
allocation library such as tcmalloc is found, its functions are
also intercepted by default. In some cases, the replacements allow
--soname-synonyms to specify one additional synonym pattern, giving
flexibility in the replacement. Or to prevent interception of all
public allocation symbols.
Currently, this flexibility is only allowed for the malloc related
functions, using the synonym somalloc. This synonym is usable for
all tools doing standard replacement of malloc related functions
(e.g. memcheck, helgrind, drd, massif, dhat).
o Alternate malloc library: to replace the malloc related
functions in a specific alternate library with soname
mymalloclib.so (and not in any others), give the option
--soname-synonyms=somalloc=mymalloclib.so. A pattern can be
used to match multiple libraries sonames. For example,
--soname-synonyms=somalloc=*tcmalloc* will match the soname of
all variants of the tcmalloc library (native, debug, profiled,
... tcmalloc variants).
Note: the soname of a elf shared library can be retrieved using
the readelf utility.
o Replacements in a statically linked library are done by using
the NONE pattern. For example, if you link with libtcmalloc.a,
and only want to intercept the malloc related functions in the
executable (and standard libraries) themselves, but not any
other shared libraries, you can give the option
--soname-synonyms=somalloc=NONE. Note that a NONE pattern will
match the main executable and any shared library having no
soname.
o To run a "default" Firefox build for Linux, in which JEMalloc
is linked in to the main executable, use
--soname-synonyms=somalloc=NONE.
o To only intercept allocation symbols in the default system
libraries, but not in any other shared library or the
executable defining public malloc or operator new related
functions use a non-existing library name like
--soname-synonyms=somalloc=nouserintercepts (where
nouserintercepts can be any non-existing library name).
o Shared library of the dynamic (runtime) linker is excluded from
searching for global public symbols, such as those for the
malloc related functions (identified by somalloc synonym).
--progress-interval=<number> [default: 0, meaning 'disabled']
This is an enhancement to Valgrind's debugging output. It is
unlikely to be of interest to end users.
When number is set to a non-zero value, Valgrind will print a
one-line progress summary every number seconds. Valid settings for
number are between 0 and 3600 inclusive. Here's some example output
with number set to 10:
PROGRESS: U 110s, W 113s, 97.3% CPU, EvC 414.79M, TIn 616.7k, TOut 0.5k, #thr 67
PROGRESS: U 120s, W 124s, 96.8% CPU, EvC 505.27M, TIn 636.6k, TOut 3.0k, #thr 64
PROGRESS: U 130s, W 134s, 97.0% CPU, EvC 574.90M, TIn 657.5k, TOut 3.0k, #thr 63
Each line shows:
o U: total user time
o W: total wallclock time
o CPU: overall average cpu use
o EvC: number of event checks. An event check is a backwards
branch in the simulated program, so this is a measure of
forward progress of the program
o TIn: number of code blocks instrumented by the JIT
o TOut: number of instrumented code blocks that have been thrown
away
o #thr: number of threads in the program
From the progress of these, it is possible to observe:
o when the program is compute bound (TIn rises slowly, EvC rises
rapidly)
o when the program is in a spinloop (TIn/TOut fixed, EvC rises
rapidly)
o when the program is JIT-bound (TIn rises rapidly)
o when the program is rapidly discarding code (TOut rises
rapidly)
o when the program is about to achieve some expected state (EvC
arrives at some value you expect)
o when the program is idling (U rises more slowly than W)
DEBUGGING VALGRIND OPTIONS
There are also some options for debugging Valgrind itself. You
shouldn't need to use them in the normal run of things. If you wish to
see the list, use the --help-debug option.
MEMCHECK OPTIONS
--leak-check=<no|summary|yes|full> [default: summary]
When enabled, search for memory leaks when the client program
finishes. If set to summary, it says how many leaks occurred. If
set to full or yes, each individual leak will be shown in detail
and/or counted as an error, as specified by the options
--show-leak-kinds and --errors-for-leak-kinds.
If --xml=yes is given, memcheck will automatically use the value
--leak-check=full. You can use --show-leak-kinds=none to reduce the
size of the xml output if you are not interested in the leak
results.
--leak-resolution=<low|med|high> [default: high]
When doing leak checking, determines how willing Memcheck is to
consider different backtraces to be the same for the purposes of
merging multiple leaks into a single leak report. When set to low,
only the first two entries need match. When med, four entries have
to match. When high, all entries need to match.
For hardcore leak debugging, you probably want to use
--leak-resolution=high together with --num-callers=40 or some such
large number.
Note that the --leak-resolution setting does not affect Memcheck's
ability to find leaks. It only changes how the results are
presented.
--show-leak-kinds=<set> [default: definite,possible]
Specifies the leak kinds to show in a full leak search, in one of
the following ways:
o a comma separated list of one or more of definite indirect
possible reachable.
o all to specify the complete set (all leak kinds). It is
equivalent to
--show-leak-kinds=definite,indirect,possible,reachable.
o none for the empty set.
--errors-for-leak-kinds=<set> [default: definite,possible]
Specifies the leak kinds to count as errors in a full leak search.
The <set> is specified similarly to --show-leak-kinds
--leak-check-heuristics=<set> [default: all]
Specifies the set of leak check heuristics to be used during leak
searches. The heuristics control which interior pointers to a block
cause it to be considered as reachable. The heuristic set is
specified in one of the following ways:
o a comma separated list of one or more of stdstring length64
newarray multipleinheritance.
o all to activate the complete set of heuristics. It is
equivalent to
--leak-check-heuristics=stdstring,length64,newarray,multipleinheritance.
o none for the empty set.
Note that these heuristics are dependent on the layout of the
objects produced by the C++ compiler. They have been tested with
some gcc versions (e.g. 4.4 and 4.7). They might not work properly
with other C++ compilers.
--show-reachable=<yes|no> , --show-possibly-lost=<yes|no>
These options provide an alternative way to specify the leak kinds
to show:
o --show-reachable=no --show-possibly-lost=yes is equivalent to
--show-leak-kinds=definite,possible.
o --show-reachable=no --show-possibly-lost=no is equivalent to
--show-leak-kinds=definite.
o --show-reachable=yes is equivalent to --show-leak-kinds=all.
Note that --show-possibly-lost=no has no effect if
--show-reachable=yes is specified.
--xtree-leak=<no|yes> [no]
If set to yes, the results for the leak search done at exit will be
output in a 'Callgrind Format' execution tree file. Note that this
automatically sets the options --leak-check=full and
--show-leak-kinds=all, to allow xtree visualisation tools such as
kcachegrind to select what kind to leak to visualise. The produced
file will contain the following events:
o RB : Reachable Bytes
o PB : Possibly lost Bytes
o IB : Indirectly lost Bytes
o DB : Definitely lost Bytes (direct plus indirect)
o DIB : Definitely Indirectly lost Bytes (subset of DB)
o RBk : reachable Blocks
o PBk : Possibly lost Blocks
o IBk : Indirectly lost Blocks
o DBk : Definitely lost Blocks
The increase or decrease for all events above will also be output
in the file to provide the delta (increase or decrease) between 2
successive leak searches. For example, iRB is the increase of the
RB event, dPBk is the decrease of PBk event. The values for the
increase and decrease events will be zero for the first leak search
done.
See Execution Trees for a detailed explanation about execution
trees.
--xtree-leak-file=<filename> [default: xtleak.kcg.%p]
Specifies that Valgrind should produce the xtree leak report in the
specified file. Any %p, %q or %n sequences appearing in the
filename are expanded in exactly the same way as they are for
--log-file. See the description of --log-file for details.
See Execution Trees for a detailed explanation about execution
trees formats.
--undef-value-errors=<yes|no> [default: yes]
Controls whether Memcheck reports uses of undefined value errors.
Set this to no if you don't want to see undefined value errors. It
also has the side effect of speeding up Memcheck somewhat.
AddrCheck (removed in Valgrind 3.1.0) functioned like Memcheck with
--undef-value-errors=no.
--track-origins=<yes|no> [default: no]
Controls whether Memcheck tracks the origin of uninitialised
values. By default, it does not, which means that although it can
tell you that an uninitialised value is being used in a dangerous
way, it cannot tell you where the uninitialised value came from.
This often makes it difficult to track down the root problem.
When set to yes, Memcheck keeps track of the origins of all
uninitialised values. Then, when an uninitialised value error is
reported, Memcheck will try to show the origin of the value. An
origin can be one of the following four places: a heap block, a
stack allocation, a client request, or miscellaneous other sources
(eg, a call to brk).
For uninitialised values originating from a heap block, Memcheck
shows where the block was allocated. For uninitialised values
originating from a stack allocation, Memcheck can tell you which
function allocated the value, but no more than that -- typically it
shows you the source location of the opening brace of the function.
So you should carefully check that all of the function's local
variables are initialised properly.
Performance overhead: origin tracking is expensive. It halves
Memcheck's speed and increases memory use by a minimum of 100MB,
and possibly more. Nevertheless it can drastically reduce the
effort required to identify the root cause of uninitialised value
errors, and so is often a programmer productivity win, despite
running more slowly.
Accuracy: Memcheck tracks origins quite accurately. To avoid very
large space and time overheads, some approximations are made. It is
possible, although unlikely, that Memcheck will report an incorrect
origin, or not be able to identify any origin.
Note that the combination --track-origins=yes and
--undef-value-errors=no is nonsensical. Memcheck checks for and
rejects this combination at startup.
--partial-loads-ok=<yes|no> [default: yes]
Controls how Memcheck handles 32-, 64-, 128- and 256-bit naturally
aligned loads from addresses for which some bytes are addressable
and others are not. When yes, such loads do not produce an address
error. Instead, loaded bytes originating from illegal addresses are
marked as uninitialised, and those corresponding to legal addresses
are handled in the normal way.
When no, loads from partially invalid addresses are treated the
same as loads from completely invalid addresses: an illegal-address
error is issued, and the resulting bytes are marked as initialised.
Note that code that behaves in this way is in violation of the ISO
C/C++ standards, and should be considered broken. If at all
possible, such code should be fixed.
--expensive-definedness-checks=<no|auto|yes> [default: auto]
Controls whether Memcheck should employ more precise but also more
expensive (time consuming) instrumentation when checking the
definedness of certain values. In particular, this affects the
instrumentation of integer adds, subtracts and equality
comparisons.
Selecting --expensive-definedness-checks=yes causes Memcheck to use
the most accurate analysis possible. This minimises false error
rates but can cause up to 30% performance degradation.
Selecting --expensive-definedness-checks=no causes Memcheck to use
the cheapest instrumentation possible. This maximises performance
but will normally give an unusably high false error rate.
The default setting, --expensive-definedness-checks=auto, is
strongly recommended. This causes Memcheck to use the minimum of
expensive instrumentation needed to achieve the same false error
rate as --expensive-definedness-checks=yes. It also enables an
instrumentation-time analysis pass which aims to further reduce the
costs of accurate instrumentation. Overall, the performance loss is
generally around 5% relative to --expensive-definedness-checks=no,
although this is strongly workload dependent. Note that the exact
instrumentation settings in this mode are architecture dependent.
--keep-stacktraces=alloc|free|alloc-and-free|alloc-then-free|none
[default: alloc-and-free]
Controls which stack trace(s) to keep for malloc'd and/or free'd
blocks.
With alloc-then-free, a stack trace is recorded at allocation time,
and is associated with the block. When the block is freed, a second
stack trace is recorded, and this replaces the allocation stack
trace. As a result, any "use after free" errors relating to this
block can only show a stack trace for where the block was freed.
With alloc-and-free, both allocation and the deallocation stack
traces for the block are stored. Hence a "use after free" error
will show both, which may make the error easier to diagnose.
Compared to alloc-then-free, this setting slightly increases
Valgrind's memory use as the block contains two references instead
of one.
With alloc, only the allocation stack trace is recorded (and
reported). With free, only the deallocation stack trace is recorded
(and reported). These values somewhat decrease Valgrind's memory
and cpu usage. They can be useful depending on the error types you
are searching for and the level of detail you need to analyse them.
For example, if you are only interested in memory leak errors, it
is sufficient to record the allocation stack traces.
With none, no stack traces are recorded for malloc and free
operations. If your program allocates a lot of blocks and/or
allocates/frees from many different stack traces, this can
significantly decrease cpu and/or memory required. Of course, few
details will be reported for errors related to heap blocks.
Note that once a stack trace is recorded, Valgrind keeps the stack
trace in memory even if it is not referenced by any block. Some
programs (for example, recursive algorithms) can generate a huge
number of stack traces. If Valgrind uses too much memory in such
circumstances, you can reduce the memory required with the options
--keep-stacktraces and/or by using a smaller value for the option
--num-callers.
If you want to use --xtree-memory=full memory profiling (see
Execution Trees), then you cannot specify --keep-stacktraces=free
or --keep-stacktraces=none.
--freelist-vol=<number> [default: 20000000]
When the client program releases memory using free (in C) or delete
(C++), that memory is not immediately made available for
re-allocation. Instead, it is marked inaccessible and placed in a
queue of freed blocks. The purpose is to defer as long as possible
the point at which freed-up memory comes back into circulation.
This increases the chance that Memcheck will be able to detect
invalid accesses to blocks for some significant period of time
after they have been freed.
This option specifies the maximum total size, in bytes, of the
blocks in the queue. The default value is twenty million bytes.
Increasing this increases the total amount of memory used by
Memcheck but may detect invalid uses of freed blocks which would
otherwise go undetected.
--freelist-big-blocks=<number> [default: 1000000]
When making blocks from the queue of freed blocks available for
re-allocation, Memcheck will in priority re-circulate the blocks
with a size greater or equal to --freelist-big-blocks. This ensures
that freeing big blocks (in particular freeing blocks bigger than
--freelist-vol) does not immediately lead to a re-circulation of
all (or a lot of) the small blocks in the free list. In other
words, this option increases the likelihood to discover dangling
pointers for the "small" blocks, even when big blocks are freed.
Setting a value of 0 means that all the blocks are re-circulated in
a FIFO order.
--workaround-gcc296-bugs=<yes|no> [default: no]
When enabled, assume that reads and writes some small distance
below the stack pointer are due to bugs in GCC 2.96, and does not
report them. The "small distance" is 256 bytes by default. Note
that GCC 2.96 is the default compiler on some ancient Linux
distributions (RedHat 7.X) and so you may need to use this option.
Do not use it if you do not have to, as it can cause real errors to
be overlooked. A better alternative is to use a more recent GCC in
which this bug is fixed.
You may also need to use this option when working with GCC 3.X or
4.X on 32-bit PowerPC Linux. This is because GCC generates code
which occasionally accesses below the stack pointer, particularly
for floating-point to/from integer conversions. This is in
violation of the 32-bit PowerPC ELF specification, which makes no
provision for locations below the stack pointer to be accessible.
This option is deprecated as of version 3.12 and may be removed
from future versions. You should instead use
--ignore-range-below-sp to specify the exact range of offsets below
the stack pointer that should be ignored. A suitable equivalent is
--ignore-range-below-sp=1024-1.
--ignore-range-below-sp=<number>-<number>
This is a more general replacement for the deprecated
--workaround-gcc296-bugs option. When specified, it causes Memcheck
not to report errors for accesses at the specified offsets below
the stack pointer. The two offsets must be positive decimal numbers
and -- somewhat counterintuitively -- the first one must be larger,
in order to imply a non-wraparound address range to ignore. For
example, to ignore 4 byte accesses at 8192 bytes below the stack
pointer, use --ignore-range-below-sp=8192-8189. Only one range may
be specified.
--show-mismatched-frees=<yes|no> [default: yes]
When enabled, Memcheck checks that heap blocks are deallocated
using a function that matches the allocating function. That is, it
expects free to be used to deallocate blocks allocated by malloc,
delete for blocks allocated by new, and delete[] for blocks
allocated by new[]. If a mismatch is detected, an error is
reported. This is in general important because in some
environments, freeing with a non-matching function can cause
crashes.
There is however a scenario where such mismatches cannot be
avoided. That is when the user provides implementations of
new/new[] that call malloc and of delete/delete[] that call free,
and these functions are asymmetrically inlined. For example,
imagine that delete[] is inlined but new[] is not. The result is
that Memcheck "sees" all delete[] calls as direct calls to free,
even when the program source contains no mismatched calls.
This causes a lot of confusing and irrelevant error reports.
--show-mismatched-frees=no disables these checks. It is not
generally advisable to disable them, though, because you may miss
real errors as a result.
--ignore-ranges=0xPP-0xQQ[,0xRR-0xSS]
Any ranges listed in this option (and multiple ranges can be
specified, separated by commas) will be ignored by Memcheck's
addressability checking.
--malloc-fill=<hexnumber>
Fills blocks allocated by malloc, new, etc, but not by calloc, with
the specified byte. This can be useful when trying to shake out
obscure memory corruption problems. The allocated area is still
regarded by Memcheck as undefined -- this option only affects its
contents. Note that --malloc-fill does not affect a block of memory
when it is used as argument to client requests
VALGRIND_MEMPOOL_ALLOC or VALGRIND_MALLOCLIKE_BLOCK.
--free-fill=<hexnumber>
Fills blocks freed by free, delete, etc, with the specified byte
value. This can be useful when trying to shake out obscure memory
corruption problems. The freed area is still regarded by Memcheck
as not valid for access -- this option only affects its contents.
Note that --free-fill does not affect a block of memory when it is
used as argument to client requests VALGRIND_MEMPOOL_FREE or
VALGRIND_FREELIKE_BLOCK.
CACHEGRIND OPTIONS
--I1=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the level 1
instruction cache.
--D1=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the level 1 data
cache.
--LL=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the last-level
cache.
--cache-sim=no|yes [yes]
Enables or disables collection of cache access and miss counts.
--branch-sim=no|yes [no]
Enables or disables collection of branch instruction and
misprediction counts. By default this is disabled as it slows
Cachegrind down by approximately 25%. Note that you cannot specify
--cache-sim=no and --branch-sim=no together, as that would leave
Cachegrind with no information to collect.
--cachegrind-out-file=<file>
Write the profile data to file rather than to the default output
file, cachegrind.out.<pid>. The %p and %q format specifiers can be
used to embed the process ID and/or the contents of an environment
variable in the name, as is the case for the core option
--log-file.
CALLGRIND OPTIONS
--callgrind-out-file=<file>
Write the profile data to file rather than to the default output
file, callgrind.out.<pid>. The %p and %q format specifiers can be
used to embed the process ID and/or the contents of an environment
variable in the name, as is the case for the core option
--log-file. When multiple dumps are made, the file name is modified
further; see below.
--dump-line=<no|yes> [default: yes]
This specifies that event counting should be performed at source
line granularity. This allows source annotation for sources which
are compiled with debug information (-g).
--dump-instr=<no|yes> [default: no]
This specifies that event counting should be performed at
per-instruction granularity. This allows for assembly code
annotation. Currently the results can only be displayed by
KCachegrind.
--compress-strings=<no|yes> [default: yes]
This option influences the output format of the profile data. It
specifies whether strings (file and function names) should be
identified by numbers. This shrinks the file, but makes it more
difficult for humans to read (which is not recommended in any
case).
--compress-pos=<no|yes> [default: yes]
This option influences the output format of the profile data. It
specifies whether numerical positions are always specified as
absolute values or are allowed to be relative to previous numbers.
This shrinks the file size.
--combine-dumps=<no|yes> [default: no]
When enabled, when multiple profile data parts are to be generated
these parts are appended to the same output file. Not recommended.
--dump-every-bb=<count> [default: 0, never]
Dump profile data every count basic blocks. Whether a dump is
needed is only checked when Valgrind's internal scheduler is run.
Therefore, the minimum setting useful is about 100000. The count is
a 64-bit value to make long dump periods possible.
--dump-before=<function>
Dump when entering function.
--zero-before=<function>
Zero all costs when entering function.
--dump-after=<function>
Dump when leaving function.
--instr-atstart=<yes|no> [default: yes]
Specify if you want Callgrind to start simulation and profiling
from the beginning of the program. When set to no, Callgrind will
not be able to collect any information, including calls, but it
will have at most a slowdown of around 4, which is the minimum
Valgrind overhead. Instrumentation can be interactively enabled via
callgrind_control -i on.
Note that the resulting call graph will most probably not contain
main, but will contain all the functions executed after
instrumentation was enabled. Instrumentation can also be
programmatically enabled/disabled. See the Callgrind include file
callgrind.h for the macro you have to use in your source code.
For cache simulation, results will be less accurate when switching
on instrumentation later in the program run, as the simulator
starts with an empty cache at that moment. Switch on event
collection later to cope with this error.
--collect-atstart=<yes|no> [default: yes]
Specify whether event collection is enabled at beginning of the
profile run.
To only look at parts of your program, you have two possibilities:
1. Zero event counters before entering the program part you want
to profile, and dump the event counters to a file after leaving
that program part.
2. Switch on/off collection state as needed to only see event
counters happening while inside of the program part you want to
profile.
The second option can be used if the program part you want to
profile is called many times. Option 1, i.e. creating a lot of
dumps is not practical here.
Collection state can be toggled at entry and exit of a given
function with the option --toggle-collect. If you use this option,
collection state should be disabled at the beginning. Note that the
specification of --toggle-collect implicitly sets
--collect-state=no.
Collection state can be toggled also by inserting the client
request CALLGRIND_TOGGLE_COLLECT ; at the needed code positions.
--toggle-collect=<function>
Toggle collection on entry/exit of function.
--collect-jumps=<no|yes> [default: no]
This specifies whether information for (conditional) jumps should
be collected. As above, callgrind_annotate currently is not able to
show you the data. You have to use KCachegrind to get jump arrows
in the annotated code.
--collect-systime=<no|yes|msec|usec|nsec> [default: no]
This specifies whether information for system call times should be
collected.
The value no indicates to record no system call information.
The other values indicate to record the number of system calls done
(sysCount event) and the elapsed time (sysTime event) spent in
system calls. The --collect-systime value gives the unit used for
sysTime : milli seconds, micro seconds or nano seconds. With the
value nsec, callgrind also records the cpu time spent during system
calls (sysCpuTime).
The value yes is a synonym of msec. The value nsec is not supported
on Darwin.
--collect-bus=<no|yes> [default: no]
This specifies whether the number of global bus events executed
should be collected. The event type "Ge" is used for these events.
--cache-sim=<yes|no> [default: no]
Specify if you want to do full cache simulation. By default, only
instruction read accesses will be counted ("Ir"). With cache
simulation, further event counters are enabled: Cache misses on
instruction reads ("I1mr"/"ILmr"), data read accesses ("Dr") and
related cache misses ("D1mr"/"DLmr"), data write accesses ("Dw")
and related cache misses ("D1mw"/"DLmw"). For more information, see
Cachegrind: a cache and branch-prediction profiler.
--branch-sim=<yes|no> [default: no]
Specify if you want to do branch prediction simulation. Further
event counters are enabled: Number of executed conditional branches
and related predictor misses ("Bc"/"Bcm"), executed indirect jumps
and related misses of the jump address predictor ("Bi"/"Bim").
HELGRIND OPTIONS
--free-is-write=no|yes [default: no]
When enabled (not the default), Helgrind treats freeing of heap
memory as if the memory was written immediately before the free.
This exposes races where memory is referenced by one thread, and
freed by another, but there is no observable synchronisation event
to ensure that the reference happens before the free.
This functionality is new in Valgrind 3.7.0, and is regarded as
experimental. It is not enabled by default because its interaction
with custom memory allocators is not well understood at present.
User feedback is welcomed.
--track-lockorders=no|yes [default: yes]
When enabled (the default), Helgrind performs lock order
consistency checking. For some buggy programs, the large number of
lock order errors reported can become annoying, particularly if
you're only interested in race errors. You may therefore find it
helpful to disable lock order checking.
--history-level=none|approx|full [default: full]
--history-level=full (the default) causes Helgrind collects enough
information about "old" accesses that it can produce two stack
traces in a race report -- both the stack trace for the current
access, and the trace for the older, conflicting access. To limit
memory usage, "old" accesses stack traces are limited to a maximum
of 8 entries, even if --num-callers value is bigger.
Collecting such information is expensive in both speed and memory,
particularly for programs that do many inter-thread synchronisation
events (locks, unlocks, etc). Without such information, it is more
difficult to track down the root causes of races. Nonetheless, you
may not need it in situations where you just want to check for the
presence or absence of races, for example, when doing regression
testing of a previously race-free program.
--history-level=none is the opposite extreme. It causes Helgrind
not to collect any information about previous accesses. This can be
dramatically faster than --history-level=full.
--history-level=approx provides a compromise between these two
extremes. It causes Helgrind to show a full trace for the later
access, and approximate information regarding the earlier access.
This approximate information consists of two stacks, and the
earlier access is guaranteed to have occurred somewhere between
program points denoted by the two stacks. This is not as useful as
showing the exact stack for the previous access (as
--history-level=full does), but it is better than nothing, and it
is almost as fast as --history-level=none.
--delta-stacktrace=no|yes [default: yes on linux amd64/x86]
This flag only has any effect at --history-level=full.
--delta-stacktrace configures the way Helgrind captures the
stacktraces for the option --history-level=full. Such a stacktrace
is typically needed each time a new piece of memory is read or
written in a basic block of instructions.
--delta-stacktrace=no causes Helgrind to compute a full history
stacktrace from the unwind info each time a stacktrace is needed.
--delta-stacktrace=yes indicates to Helgrind to derive a new
stacktrace from the previous stacktrace, as long as there was no
call instruction, no return instruction, or any other instruction
changing the call stack since the previous stacktrace was captured.
If no such instruction was executed, the new stacktrace can be
derived from the previous stacktrace by just changing the top frame
to the current program counter. This option can speed up Helgrind
by 25% when using --history-level=full.
The following aspects have to be considered when using
--delta-stacktrace=yes :
o In some cases (for example in a function prologue), the
valgrind unwinder might not properly unwind the stack, due to
some limitations and/or due to wrong unwind info. When using
--delta-stacktrace=yes, the wrong stack trace captured in the
function prologue will be kept till the next call or return.
o On the other hand, --delta-stacktrace=yes sometimes helps to
obtain a correct stacktrace, for example when the unwind info
allows a correct stacktrace to be done in the beginning of the
sequence, but not later on in the instruction sequence.
o Determining which instructions are changing the callstack is
partially based on platform dependent heuristics, which have to
be tuned/validated specifically for the platform. Also,
unwinding in a function prologue must be good enough to allow
using --delta-stacktrace=yes. Currently, the option
--delta-stacktrace=yes has been reasonably validated only on
linux x86 32 bits and linux amd64 64 bits. For more details
about how to validate --delta-stacktrace=yes, see debug option
--hg-sanity-flags and the function check_cached_rcec_ok in
libhb_core.c.
--conflict-cache-size=N [default: 1000000]
This flag only has any effect at --history-level=full.
Information about "old" conflicting accesses is stored in a cache
of limited size, with LRU-style management. This is necessary
because it isn't practical to store a stack trace for every single
memory access made by the program. Historical information on not
recently accessed locations is periodically discarded, to free up
space in the cache.
This option controls the size of the cache, in terms of the number
of different memory addresses for which conflicting access
information is stored. If you find that Helgrind is showing race
errors with only one stack instead of the expected two stacks, try
increasing this value.
The minimum value is 10,000 and the maximum is 30,000,000 (thirty
times the default value). Increasing the value by 1 increases
Helgrind's memory requirement by very roughly 100 bytes, so the
maximum value will easily eat up three extra gigabytes or so of
memory.
--check-stack-refs=no|yes [default: yes]
By default Helgrind checks all data memory accesses made by your
program. This flag enables you to skip checking for accesses to
thread stacks (local variables). This can improve performance, but
comes at the cost of missing races on stack-allocated data.
--ignore-thread-creation=<yes|no> [default: no]
Controls whether all activities during thread creation should be
ignored. By default enabled only on Solaris. Solaris provides
higher throughput, parallelism and scalability than other operating
systems, at the cost of more fine-grained locking activity. This
means for example that when a thread is created under glibc, just
one big lock is used for all thread setup. Solaris libc uses
several fine-grained locks and the creator thread resumes its
activities as soon as possible, leaving for example stack and TLS
setup sequence to the created thread. This situation confuses
Helgrind as it assumes there is some false ordering in place
between creator and created thread; and therefore many types of
race conditions in the application would not be reported. To
prevent such false ordering, this command line option is set to yes
by default on Solaris. All activity (loads, stores, client
requests) is therefore ignored during:
o pthread_create() call in the creator thread
o thread creation phase (stack and TLS setup) in the created
thread
Also new memory allocated during thread creation is untracked, that
is race reporting is suppressed there. DRD does the same thing
implicitly. This is necessary because Solaris libc caches many
objects and reuses them for different threads and that confuses
Helgrind.
DRD OPTIONS
--check-stack-var=<yes|no> [default: no]
Controls whether DRD detects data races on stack variables.
Verifying stack variables is disabled by default because most
programs do not share stack variables over threads.
--exclusive-threshold=<n> [default: off]
Print an error message if any mutex or writer lock has been held
longer than the time specified in milliseconds. This option enables
the detection of lock contention.
--join-list-vol=<n> [default: 10]
Data races that occur between a statement at the end of one thread
and another thread can be missed if memory access information is
discarded immediately after a thread has been joined. This option
allows one to specify for how many joined threads memory access
information should be retained.
--first-race-only=<yes|no> [default: no]
Whether to report only the first data race that has been detected
on a memory location or all data races that have been detected on a
memory location.
--free-is-write=<yes|no> [default: no]
Whether to report races between accessing memory and freeing
memory. Enabling this option may cause DRD to run slightly slower.
Notes:
o Don't enable this option when using custom memory allocators
that use the VG_USERREQ__MALLOCLIKE_BLOCK and
VG_USERREQ__FREELIKE_BLOCK because that would result in false
positives.
o Don't enable this option when using reference-counted objects
because that will result in false positives, even when that
code has been annotated properly with ANNOTATE_HAPPENS_BEFORE
and ANNOTATE_HAPPENS_AFTER. See e.g. the output of the
following command for an example: valgrind --tool=drd
--free-is-write=yes drd/tests/annotate_smart_pointer.
--report-signal-unlocked=<yes|no> [default: yes]
Whether to report calls to pthread_cond_signal and
pthread_cond_broadcast where the mutex associated with the signal
through pthread_cond_wait or pthread_cond_timed_waitis not locked
at the time the signal is sent. Sending a signal without holding a
lock on the associated mutex is a common programming error which
can cause subtle race conditions and unpredictable behavior. There
exist some uncommon synchronization patterns however where it is
safe to send a signal without holding a lock on the associated
mutex.
--segment-merging=<yes|no> [default: yes]
Controls segment merging. Segment merging is an algorithm to limit
memory usage of the data race detection algorithm. Disabling
segment merging may improve the accuracy of the so-called 'other
segments' displayed in race reports but can also trigger an out of
memory error.
--segment-merging-interval=<n> [default: 10]
Perform segment merging only after the specified number of new
segments have been created. This is an advanced configuration
option that allows one to choose whether to minimize DRD's memory
usage by choosing a low value or to let DRD run faster by choosing
a slightly higher value. The optimal value for this parameter
depends on the program being analyzed. The default value works well
for most programs.
--shared-threshold=<n> [default: off]
Print an error message if a reader lock has been held longer than
the specified time (in milliseconds). This option enables the
detection of lock contention.
--show-confl-seg=<yes|no> [default: yes]
Show conflicting segments in race reports. Since this information
can help to find the cause of a data race, this option is enabled
by default. Disabling this option makes the output of DRD more
compact.
--show-stack-usage=<yes|no> [default: no]
Print stack usage at thread exit time. When a program creates a
large number of threads it becomes important to limit the amount of
virtual memory allocated for thread stacks. This option makes it
possible to observe how much stack memory has been used by each
thread of the client program. Note: the DRD tool itself allocates
some temporary data on the client thread stack. The space necessary
for this temporary data must be allocated by the client program
when it allocates stack memory, but is not included in stack usage
reported by DRD.
--ignore-thread-creation=<yes|no> [default: no]
Controls whether all activities during thread creation should be
ignored. By default enabled only on Solaris. Solaris provides
higher throughput, parallelism and scalability than other operating
systems, at the cost of more fine-grained locking activity. This
means for example that when a thread is created under glibc, just
one big lock is used for all thread setup. Solaris libc uses
several fine-grained locks and the creator thread resumes its
activities as soon as possible, leaving for example stack and TLS
setup sequence to the created thread. This situation confuses DRD
as it assumes there is some false ordering in place between creator
and created thread; and therefore many types of race conditions in
the application would not be reported. To prevent such false
ordering, this command line option is set to yes by default on
Solaris. All activity (loads, stores, client requests) is therefore
ignored during:
o pthread_create() call in the creator thread
o thread creation phase (stack and TLS setup) in the created
thread
--trace-addr=<address> [default: none]
Trace all load and store activity for the specified address. This
option may be specified more than once.
--ptrace-addr=<address> [default: none]
Trace all load and store activity for the specified address and
keep doing that even after the memory at that address has been
freed and reallocated.
--trace-alloc=<yes|no> [default: no]
Trace all memory allocations and deallocations. May produce a huge
amount of output.
--trace-barrier=<yes|no> [default: no]
Trace all barrier activity.
--trace-cond=<yes|no> [default: no]
Trace all condition variable activity.
--trace-fork-join=<yes|no> [default: no]
Trace all thread creation and all thread termination events.
--trace-hb=<yes|no> [default: no]
Trace execution of the ANNOTATE_HAPPENS_BEFORE(),
ANNOTATE_HAPPENS_AFTER() and ANNOTATE_HAPPENS_DONE() client
requests.
--trace-mutex=<yes|no> [default: no]
Trace all mutex activity.
--trace-rwlock=<yes|no> [default: no]
Trace all reader-writer lock activity.
--trace-semaphore=<yes|no> [default: no]
Trace all semaphore activity.
MASSIF OPTIONS
--heap=<yes|no> [default: yes]
Specifies whether heap profiling should be done.
--heap-admin=<size> [default: 8]
If heap profiling is enabled, gives the number of administrative
bytes per block to use. This should be an estimate of the average,
since it may vary. For example, the allocator used by glibc on
Linux requires somewhere between 4 to 15 bytes per block, depending
on various factors. That allocator also requires admin space for
freed blocks, but Massif cannot account for this.
--stacks=<yes|no> [default: no]
Specifies whether stack profiling should be done. This option slows
Massif down greatly, and so is off by default. Note that Massif
assumes that the main stack has size zero at start-up. This is not
true, but doing otherwise accurately is difficult. Furthermore,
starting at zero better indicates the size of the part of the main
stack that a user program actually has control over.
--pages-as-heap=<yes|no> [default: no]
Tells Massif to profile memory at the page level rather than at the
malloc'd block level. See above for details.
--depth=<number> [default: 30]
Maximum depth of the allocation trees recorded for detailed
snapshots. Increasing it will make Massif run somewhat more slowly,
use more memory, and produce bigger output files.
--alloc-fn=<name>
Functions specified with this option will be treated as though they
were a heap allocation function such as malloc. This is useful for
functions that are wrappers to malloc or new, which can fill up the
allocation trees with uninteresting information. This option can be
specified multiple times on the command line, to name multiple
functions.
Note that the named function will only be treated this way if it is
the top entry in a stack trace, or just below another function
treated this way. For example, if you have a function malloc1 that
wraps malloc, and malloc2 that wraps malloc1, just specifying
--alloc-fn=malloc2 will have no effect. You need to specify
--alloc-fn=malloc1 as well. This is a little inconvenient, but the
reason is that checking for allocation functions is slow, and it
saves a lot of time if Massif can stop looking through the stack
trace entries as soon as it finds one that doesn't match rather
than having to continue through all the entries.
Note that C++ names are demangled. Note also that overloaded C++
names must be written in full. Single quotes may be necessary to
prevent the shell from breaking them up. For example:
--alloc-fn='operator new(unsigned, std::nothrow_t const&)'
--ignore-fn=<name>
Any direct heap allocation (i.e. a call to malloc, new, etc, or a
call to a function named by an --alloc-fn option) that occurs in a
function specified by this option will be ignored. This is mostly
useful for testing purposes. This option can be specified multiple
times on the command line, to name multiple functions.
Any realloc of an ignored block will also be ignored, even if the
realloc call does not occur in an ignored function. This avoids the
possibility of negative heap sizes if ignored blocks are shrunk
with realloc.
The rules for writing C++ function names are the same as for
--alloc-fn above.
--threshold=<m.n> [default: 1.0]
The significance threshold for heap allocations, as a percentage of
total memory size. Allocation tree entries that account for less
than this will be aggregated. Note that this should be specified in
tandem with ms_print's option of the same name.
--peak-inaccuracy=<m.n> [default: 1.0]
Massif does not necessarily record the actual global memory
allocation peak; by default it records a peak only when the global
memory allocation size exceeds the previous peak by at least 1.0%.
This is because there can be many local allocation peaks along the
way, and doing a detailed snapshot for every one would be expensive
and wasteful, as all but one of them will be later discarded. This
inaccuracy can be changed (even to 0.0%) via this option, but
Massif will run drastically slower as the number approaches zero.
--time-unit=<i|ms|B> [default: i]
The time unit used for the profiling. There are three
possibilities: instructions executed (i), which is good for most
cases; real (wallclock) time (ms, i.e. milliseconds), which is
sometimes useful; and bytes allocated/deallocated on the heap
and/or stack (B), which is useful for very short-run programs, and
for testing purposes, because it is the most reproducible across
different machines.
--detailed-freq=<n> [default: 10]
Frequency of detailed snapshots. With --detailed-freq=1, every
snapshot is detailed.
--max-snapshots=<n> [default: 100]
The maximum number of snapshots recorded. If set to N, for all
programs except very short-running ones, the final number of
snapshots will be between N/2 and N.
--massif-out-file=<file> [default: massif.out.%p]
Write the profile data to file rather than to the default output
file, massif.out.<pid>. The %p and %q format specifiers can be used
to embed the process ID and/or the contents of an environment
variable in the name, as is the case for the core option
--log-file.
BBV OPTIONS
--bb-out-file=<name> [default: bb.out.%p]
This option selects the name of the basic block vector file. The %p
and %q format specifiers can be used to embed the process ID and/or
the contents of an environment variable in the name, as is the case
for the core option --log-file.
--pc-out-file=<name> [default: pc.out.%p]
This option selects the name of the PC file. This file holds
program counter addresses and function name info for the various
basic blocks. This can be used in conjunction with the basic block
vector file to fast-forward via function names instead of just
instruction counts. The %p and %q format specifiers can be used to
embed the process ID and/or the contents of an environment variable
in the name, as is the case for the core option --log-file.
--interval-size=<number> [default: 100000000]
This option selects the size of the interval to use. The default is
100 million instructions, which is a commonly used value. Other
sizes can be used; smaller intervals can help programs with
finer-grained phases. However smaller interval size can lead to
accuracy issues due to warm-up effects (When fast-forwarding the
various architectural features will be un-initialized, and it will
take some number of instructions before they "warm up" to the state
a full simulation would be at without the fast-forwarding. Large
interval sizes tend to mitigate this.)
--instr-count-only [default: no]
This option tells the tool to only display instruction count
totals, and to not generate the actual basic block vector file.
This is useful for debugging, and for gathering instruction count
info without generating the large basic block vector files.
LACKEY OPTIONS
--basic-counts=<no|yes> [default: yes]
When enabled, Lackey prints the following statistics and
information about the execution of the client program:
1. The number of calls to the function specified by the --fnname
option (the default is main). If the program has had its
symbols stripped, the count will always be zero.
2. The number of conditional branches encountered and the number
and proportion of those taken.
3. The number of superblocks entered and completed by the program.
Note that due to optimisations done by the JIT, this is not at
all an accurate value.
4. The number of guest (x86, amd64, ppc, etc.) instructions and IR
statements executed. IR is Valgrind's RISC-like intermediate
representation via which all instrumentation is done.
5. Ratios between some of these counts.
6. The exit code of the client program.
--detailed-counts=<no|yes> [default: no]
When enabled, Lackey prints a table containing counts of loads,
stores and ALU operations, differentiated by their IR types. The IR
types are identified by their IR name ("I1", "I8", ... "I128",
"F32", "F64", and "V128").
--trace-mem=<no|yes> [default: no]
When enabled, Lackey prints the size and address of almost every
memory access made by the program. See the comments at the top of
the file lackey/lk_main.c for details about the output format, how
it works, and inaccuracies in the address trace. Note that this
option produces immense amounts of output.
--trace-superblocks=<no|yes> [default: no]
When enabled, Lackey prints out the address of every superblock (a
single entry, multiple exit, linear chunk of code) executed by the
program. This is primarily of interest to Valgrind developers. See
the comments at the top of the file lackey/lk_main.c for details
about the output format. Note that this option produces large
amounts of output.
--fnname=<name> [default: main]
Changes the function for which calls are counted when
--basic-counts=yes is specified.
SEE ALSO
cg_annotate(1), callgrind_annotate(1), callgrind_control(1),
ms_print(1), $INSTALL/share/doc/valgrind/html/index.html or
http://www.valgrind.org/docs/manual/index.html, Debugging your program
using Valgrind's gdbserver and GDB[1] vgdb[2], Valgrind monitor
commands[3], The Commentary[4], Scheduling and Multi-Thread
Performance[5], Cachegrind: a cache and branch-prediction profiler[6].
Execution Trees[7]
AUTHOR
See the AUTHORS file in the valgrind distribution for a comprehensive
list of authors.
This manpage was written by Andres Roldan <aroldan@debian.org> and the
Valgrind developers.
NOTES
1. Debugging your program using Valgrind's gdbserver and GDB
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.gdbserver
2. vgdb
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.vgdb
3. Valgrind monitor commands
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.valgrind-monitor-commands
4. The Commentary
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.comment
5. Scheduling and Multi-Thread Performance
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.pthreads_perf_sched
6. Cachegrind: a cache and branch-prediction profiler
http://www.valgrind.org/docs/manual/cg-manual.html
7. Execution Trees
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.xtree
Release 3.16.1 06/28/2020 VALGRIND(1)