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.
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.
--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.
--track-fds=<yes|no> [default: no]
When enabled, Valgrind will print out a list of open file
descriptors on exit. 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.
%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.
--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 Ptrcheck. 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 50. 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.
--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.
--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.
--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] ----
The prompt's behaviour is the same as for the --db-attach option
(see below).
If you choose to, Valgrind will print out 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.
--db-attach=<yes|no> [default: no]
When enabled, Valgrind will pause after every error shown and print
the line:
---- Attach to debugger ? --- [Return/N/n/Y/y/C/c] ----
Pressing Ret, or N Ret or n Ret, causes Valgrind not to start a
debugger for this error.
Pressing Y Ret or y Ret causes Valgrind to start a debugger for the
program at this point. When you have finished with the debugger,
quit from it, and the program will continue. Trying to continue
from inside the debugger doesn't work.
C Ret or c Ret causes Valgrind not to start a debugger, and not to
ask again.
--db-command=<command> [default: gdb -nw %f %p]
Specify the debugger to use with the --db-attach command. The
default debugger is GDB. This option is a template that is expanded
by Valgrind at runtime. %f is replaced with the executable's file
name and %p is replaced by the process ID of the executable.
This specifies how Valgrind will invoke the debugger. By default it
will use whatever GDB is detected at build time, which is usually
/usr/bin/gdb. Using this command, you can specify some alternative
command to invoke the debugger you want to use.
The command string given can include one or instances of the %p and
%f expansions. Each instance of %p expands to the PID of the
process to be debugged and each instance of %f expands to the path
to the executable for the process to be debugged.
Since <command> is likely to contain spaces, you will need to put
this entire option in quotes to ensure it is correctly handled by
the shell.
--input-fd=<number> [default: 0, stdin]
When using --db-attach=yes or --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 [no]
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 the 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. On
AIX5 the allowed stack size is restricted to 128MB.
--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.
MALLOC()-RELATED OPTIONS
For tools that use their own version of malloc (e.g. Memcheck and
Massif), 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.
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 these.
--smc-check=<none|stack|all> [default: stack]
This option controls Valgrind's detection of self-modifying code.
If no checking is done, if 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.
Valgrind has three levels of self-modifying code detection: no
detection, detect self-modifying code on the stack (which used by
GCC to implement nested functions), or detect self-modifying code
everywhere. Note that the default option will catch the vast
majority of cases. The main case it will not catch is programs such
as JIT compilers that dynamically generate code and subsequently
overwrite part or all of it. Running with all will slow Valgrind
down greatly. Running with none will rarely speed things up, since
very little code gets put on the stack for most programs. The
VALGRIND_DISCARD_TRANSLATIONS client request is an alternative to
--smc-check=all that requires more effort but is much faster.
Some architectures (including ppc32 and ppc64) require programs
which create code at runtime to flush the instruction cache in
between code generation and first use. Valgrind observes and
honours such instructions. Hence, on ppc32/Linux and ppc64/Linux,
Valgrind always provides complete, transparent support for
self-modifying code. It is only on platforms such as x86/Linux,
AMD64/Linux and x86/Darwin that you need to use this option.
--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 down and
makes it use 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:
==15516== Uninitialised byte(s) found during client check request
==15516== at 0x400633: croak (varinfo1.c:28)
==15516== by 0x4006B2: main (varinfo1.c:55)
==15516== Address 0x60103b is 7 bytes inside data symbol "global_i2"
==15516==
==15516== Uninitialised byte(s) found during client check request
==15516== at 0x400633: croak (varinfo1.c:28)
==15516== by 0x4006BC: main (varinfo1.c:56)
==15516== Address 0x7fefffefc is on thread 1's stack
And here are the same errors with --read-var-info=yes:
==15522== Uninitialised byte(s) found during client check request
==15522== at 0x400633: croak (varinfo1.c:28)
==15522== by 0x4006B2: main (varinfo1.c:55)
==15522== Location 0x60103b is 0 bytes inside global_i2[7],
==15522== a global variable declared at varinfo1.c:41
==15522==
==15522== Uninitialised byte(s) found during client check request
==15522== at 0x400633: croak (varinfo1.c:28)
==15522== by 0x4006BC: main (varinfo1.c:56)
==15522== Location 0x7fefffefc is 0 bytes inside local var "local"
==15522== declared at varinfo1.c:46, in frame #1 of thread 1
--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.
--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 initialized when writing. Without this, using
some device drivers with a large number of strange ioctl
commands becomes very tiresome.
o enable-inner: Enable some special magic needed when the program
being run is itself Valgrind.
--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.
--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.
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, it also gives details of each individual leak.
--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-reachable=<yes|no> [default: no]
When disabled, the memory leak detector only shows "definitely
lost" and "possibly lost" blocks. When enabled, the leak detector
also shows "reachable" and "indirectly lost" blocks. (In other
words, it shows all blocks, except suppressed ones, so --show-all
would be a better name for it.)
--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.
--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: no]
Controls how Memcheck handles word-sized, word-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 the
ISO C/C++ standards, and should be considered broken. If at all
possible, such code should be fixed. This option should be used
only as a last resort.
--freelist-vol=<number> [default: 10000000]
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 ten 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.
--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.
--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.
--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.
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.
--L2=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the level 2 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
programatically 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> [default: no]
This specifies whether information for system call times should be
collected.
--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"/"I2mr"), data read accesses ("Dr") and
related cache misses ("D1mr"/"D2mr"), data write accesses ("Dw")
and related cache misses ("D1mw"/"D2mw"). For more information, see
???.
--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
--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.
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.
--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.
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.
--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.
--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 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 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.
--trace-addr=<address> [default: none]
Trace all load and store activity for the specified address. This
option may be specified more than once.
--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-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.
--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.
PTRCHECK OPTIONS
--enable-sg-checks=no|yes [default: yes]
By default, Ptrcheck checks for overruns of stack, global and heap
arrays. With --enable-sg-checks=no, the stack and global array
checks are omitted, and only heap checking is performed. This can
be useful because the stack and global checks are quite expensive,
so omitting them speeds Ptrcheck up a lot.
--partial-loads-ok=<yes|no> [default: no]
This option has the same meaning as it does for Memcheck.
Controls how Ptrcheck handles word-sized, word-aligned loads which
partially overlap the end of heap blocks -- that is, some of the
bytes in the word are validly addressable, but others are not. When
yes, such loads do not produce an address error. When no (the
default), loads from partially invalid addresses are treated the
same as loads from completely invalid addresses: an illegal heap
access error is issued.
Note that code that behaves in this way is in violation of the the
ISO C/C++ standards, and should be considered broken. If at all
possible, such code should be fixed. This option should be used
only as a last resort.
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.
AUTHOR
The Valgrind developers.
This manpage was written by Andres Roldan <aroldan@debian.org> and the
Valgrind developers.