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Valgrind is a dynamic analysis tool which detects memory errors and memory leaks. It is spiritually the predecessor of modern debugging tools like AddressSanitizer and LeakSanitizer, but remains relevant for debugging applications today because of its thoroughness and ease of setup (no need to recompile applications). They cover similar but not identical usecases [1].


For better support for Valgrind in system applications, consider enabling valgrind. For example, this will make dev-lang/python detect when Valgrind is in use and switch allocators from its internal pymalloc to valgrind's, giving far better output.

USE flags

USE flags for dev-debug/valgrind An open-source memory debugger for GNU/Linux

mpi Add MPI (Message Passing Interface) layer to the apps that support it
verify-sig Verify upstream signatures on distfiles


root #emerge --ask dev-debug/valgrind


Environment variables



  • ~/.valgrindrc - Local (per user) configuration file.
  • ./.valgrindrc - Local (per project/directory) configuration file.


Valgrind is actually a suite of tools, but for many people, "Valgrind" is synonymous with the default tool memcheck. The following tools are available, which can be selected with valgrind --tool=name:

  • cachegrind (cache and branch-prediction profiler)
  • callgrind (call-graph generating cache and branch prediction profiler)
  • dhat (dynamic heap analysis tool)
  • drd (thread safety analysis)
  • helgrind (thread error detector)
  • lackey (example tool, can be used to analyze a specific function)
  • massif (heap memory profiler)
  • memcheck (memory error detector)

Using Valgrind with applications is easy, simply run valgrind /path/to/application. No recompilation is needed!

For example, to run Valgrind on uptime:

user $valgrind uptime
==3064010== Memcheck, a memory error detector
==3064010== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==3064010== Using Valgrind-3.20.0 and LibVEX; rerun with -h for copyright info
==3064010== Command: uptime
 03:35:26 up 4 days,  6:58,  1 user,  load average: 0.15, 2.26, 10.93
==3064010== HEAP SUMMARY:
==3064010==     in use at exit: 0 bytes in 0 blocks
==3064010==   total heap usage: 57 allocs, 57 frees, 31,824 bytes allocated
==3064010== All heap blocks were freed -- no leaks are possible
==3064010== For lists of detected and suppressed errors, rerun with: -s
==3064010== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

The output states that uptime ran successfully with no detected memory leaks and no memory safety issues (no out-of-bounds access, etc).


user $valgrind --help
usage: valgrind [options] prog-and-args

  tool-selection option, with default in [ ]:
    --tool=<name>             use the Valgrind tool named <name> [memcheck]

  basic user options for all Valgrind tools, with defaults in [ ]:
    -h --help                 show this message
    --help-debug              show this message, plus debugging options
    --help-dyn-options        show the dynamically changeable options
    --version                 show version
    -q --quiet                run silently; only print error msgs
    -v --verbose              be more verbose -- show misc extra info
    --trace-children=no|yes   Valgrind-ise child processes (follow execve)? [no]
    --trace-children-skip=patt1,patt2,...    specifies a list of executables
                              that --trace-children=yes should not trace into
    --trace-children-skip-by-arg=patt1,patt2,...   same as --trace-children-skip=
                              but check the argv[] entries for children, rather
                              than the exe name, to make a follow/no-follow decision
    --child-silent-after-fork=no|yes omit child output between fork & exec? [no]
    --vgdb=no|yes|full        activate gdbserver? [yes]
                              full is slower but provides precise watchpoint/step
    --vgdb-error=<number>     invoke gdbserver after <number> errors [999999999]
                              to get started quickly, use --vgdb-error=0
                              and follow the on-screen directions
    --vgdb-stop-at=event1,event2,... invoke gdbserver for given events [none]
         where event is one of:
           startup exit abexit valgrindabexit all none
    --track-fds=no|yes|all    track open file descriptors? [no]
                              all includes reporting stdin, stdout and stderr
    --time-stamp=no|yes       add timestamps to log messages? [no]
    --log-fd=<number>         log messages to file descriptor [2=stderr]
    --log-file=<file>         log messages to <file>
    --log-socket=ipaddr:port  log messages to socket ipaddr:port
    --enable-debuginfod=no|yes query debuginfod servers for missing
                              debuginfo [yes]

  user options for Valgrind tools that report errors:
    --xml=yes                 emit error output in XML (some tools only)
    --xml-fd=<number>         XML output to file descriptor
    --xml-file=<file>         XML output to <file>
    --xml-socket=ipaddr:port  XML output to socket ipaddr:port
    --xml-user-comment=STR    copy STR verbatim into XML output
    --demangle=no|yes         automatically demangle C++ names? [yes]
    --num-callers=<number>    show <number> callers in stack traces [12]
    --error-limit=no|yes      stop showing new errors if too many? [yes]
    --exit-on-first-error=no|yes exit code on the first error found? [no]
    --error-exitcode=<number> exit code to return if errors found [0=disable]
    --error-markers=<begin>,<end> add lines with begin/end markers before/after
                              each error output in plain text mode [none]
    --show-error-list=no|yes  show detected errors list and
                              suppression counts at exit [no]
    -s                        same as --show-error-list=yes
    --keep-debuginfo=no|yes   Keep symbols etc for unloaded code [no]
                              This allows saved stack traces (e.g. memory leaks)
                              to include file/line info for code that has been
                              dlclose'd (or similar)
    --show-below-main=no|yes  continue stack traces below main() [no]
                              load default suppressions [yes]
    --suppressions=<filename> suppress errors described in <filename>
    --gen-suppressions=no|yes|all    print suppressions for errors? [no]
    --input-fd=<number>       file descriptor for input [0=stdin]
    --dsymutil=no|yes         run dsymutil on Mac OS X when helpful? [yes]
    --max-stackframe=<number> assume stack switch for SP changes larger
                              than <number> bytes [2000000]
    --main-stacksize=<number> set size of main thread's stack (in bytes)
                              [min(max(current 'ulimit' value,1MB),16MB)]

  user options for Valgrind tools that replace malloc:
    --alignment=<number>      set minimum alignment of heap allocations [16]
    --redzone-size=<number>   set minimum size of redzones added before/after
                              heap blocks (in bytes). [16]
    --xtree-memory=none|allocs|full   profile heap memory in an xtree [none]
                              and produces a report at the end of the execution
                              none: no profiling, allocs: current allocated
                              size/blocks, full: profile current and cumulative
                              allocated size/blocks and freed size/blocks.
    --xtree-memory-file=<file>   xtree memory report file [xtmemory.kcg.%p]

  uncommon user options for all Valgrind tools:
    --fullpath-after=         (with nothing after the '=')
                              show full source paths in call stacks
    --fullpath-after=string   like --fullpath-after=, but only show the
                              part of the path after 'string'.  Allows removal
                              of path prefixes.  Use this flag multiple times
                              to specify a set of prefixes to remove.
    --extra-debuginfo-path=path    absolute path to search for additional
                              debug symbols, in addition to existing default
                              well known search paths.
    --debuginfo-server=ipaddr:port    also query this server
                              (valgrind-di-server) for debug symbols
    --allow-mismatched-debuginfo=no|yes  [no]
                              for the above two flags only, accept debuginfo
                              objects that don't "match" the main object
    --smc-check=none|stack|all|all-non-file [all-non-file]
                              checks for self-modifying code: none, only for
                              code found in stacks, for all code, or for all
                              code except that from file-backed mappings
    --read-inline-info=yes|no read debug info about inlined function calls
                              and use it to do better stack traces.
                              [yes] on Linux/Android/Solaris for the tools
                              Memcheck/Massif/Helgrind/DRD only.
                              [no] for all other tools and platforms.
    --read-var-info=yes|no    read debug info on stack and global variables
                              and use it to print better error messages in
                              tools that make use of it (Memcheck, Helgrind,
                              DRD) [no]
    --vgdb-poll=<number>      gdbserver poll max every <number> basic blocks [5000]
    --vgdb-shadow-registers=no|yes   let gdb see the shadow registers [no]
    --vgdb-prefix=<prefix>    prefix for vgdb FIFOs [/tmp/vgdb-pipe]
    --run-libc-freeres=no|yes free up glibc memory at exit on Linux? [yes]
    --run-cxx-freeres=no|yes  free up libstdc++ memory at exit on Linux
                              and Solaris? [yes]
    --sim-hints=hint1,hint2,...  activate unusual sim behaviours [none]
         where hint is one of:
           lax-ioctls lax-doors fuse-compatible enable-outer
           no-inner-prefix no-nptl-pthread-stackcache fallback-llsc none
    --fair-sched=no|yes|try   schedule threads fairly on multicore systems [no]
         handle non-standard kernel variants [none]
         where variant is one of:
           bproc android-no-hw-tls
           android-gpu-sgx5xx android-gpu-adreno3xx none
    --merge-recursive-frames=<number>  merge frames between identical
           program counters in max <number> frames) [0]
    --num-transtab-sectors=<number> size of translated code cache [32]
           more sectors may increase performance, but use more memory.
    --avg-transtab-entry-size=<number> avg size in bytes of a translated
           basic block [0, meaning use tool provided default]
    --aspace-minaddr=0xPP     avoid mapping memory below 0xPP [guessed]
    --valgrind-stacksize=<number> size of valgrind (host) thread's stack
                               (in bytes) [1048576]
    --show-emwarns=no|yes     show warnings about emulation limits? [no]
    --require-text-symbol=:sonamepattern:symbolpattern    abort run if the
                              stated shared object doesn't have the stated
                              text symbol.  Patterns can contain ? and *.
    --soname-synonyms=syn1=pattern1,syn2=pattern2,... synonym soname
              specify patterns for function wrapping or replacement.
              To use a non-libc malloc library that is
                  in the main exe:  --soname-synonyms=somalloc=NONE
    --sigill-diagnostics=yes|no  warn about illegal instructions? [yes]
    --unw-stack-scan-thresh=<number>   Enable stack-scan unwind if fewer
                  than <number> good frames found  [0, meaning "disabled"]
                  NOTE: stack scanning is only available on arm-linux.
    --unw-stack-scan-frames=<number>   Max number of frames that can be
                  recovered by stack scanning [5]
    --resync-filter=no|yes|verbose [yes on MacOS, no on other OSes]
              attempt to avoid expensive address-space-resync operations
    --max-threads=<number>    maximum number of threads that valgrind can
                              handle [500]

  user options for Memcheck:
    --leak-check=no|summary|full     search for memory leaks at exit?  [summary]
    --leak-resolution=low|med|high   differentiation of leak stack traces [high]
    --show-leak-kinds=kind1,kind2,.. which leak kinds to show?
    --errors-for-leak-kinds=kind1,kind2,..  which leak kinds are errors?
        where kind is one of:
          definite indirect possible reachable all none
    --leak-check-heuristics=heur1,heur2,... which heuristics to use for
        improving leak search false positive [all]
        where heur is one of:
          stdstring length64 newarray multipleinheritance all none
    --show-reachable=yes             same as --show-leak-kinds=all
    --show-reachable=no --show-possibly-lost=yes
                                     same as --show-leak-kinds=definite,possible
    --show-reachable=no --show-possibly-lost=no
                                     same as --show-leak-kinds=definite
    --xtree-leak=no|yes              output leak result in xtree format? [no]
    --xtree-leak-file=<file>         xtree leak report file [xtleak.kcg.%p]
    --undef-value-errors=no|yes      check for undefined value errors [yes]
    --track-origins=no|yes           show origins of undefined values? [no]
    --partial-loads-ok=no|yes        too hard to explain here; see manual [yes]
                                     Use extra-precise definedness tracking [auto]
    --freelist-vol=<number>          volume of freed blocks queue     [20000000]
    --freelist-big-blocks=<number>   releases first blocks with size>= [1000000]
    --workaround-gcc296-bugs=no|yes  self explanatory [no].  Deprecated.
                                     Use --ignore-range-below-sp instead.
    --ignore-ranges=0xPP-0xQQ[,0xRR-0xSS]   assume given addresses are OK
    --ignore-range-below-sp=<number>-<number>  do not report errors for
                                     accesses at the given offsets below SP
    --malloc-fill=<hexnumber>        fill malloc'd areas with given value
    --free-fill=<hexnumber>          fill free'd areas with given value
        stack trace(s) to keep for malloc'd/free'd areas       [alloc-and-free]
    --show-mismatched-frees=no|yes   show frees that don't match the allocator? [yes]

  Extra options read from ~/.valgrindrc, $VALGRIND_OPTS, ./.valgrindrc

  Memcheck is Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
  Valgrind is Copyright (C) 2000-2017, and GNU GPL'd, by Julian Seward et al.
  LibVEX is Copyright (C) 2004-2017, and GNU GPL'd, by OpenWorks LLP et al.

  Bug reports, feedback, admiration, abuse, etc, to:


Valgrind often needs debug information of the C library to perform function redirection. For this, create the package debug environment described above and apply it for sys-libs/glibc (or sys-libs/musl as needed).

First, debugedit should be installed:

root #emerge --ask dev-util/debugedit

Configure Portage to build selected packages with (enhanced) debugging symbols (-ggdb3) and not to strip them:

CFLAGS="${CFLAGS} -ggdb3"
FEATURES="${FEATURES} splitdebug compressdebug -nostrip"
FEATURES="${FEATURES} installsources"

Enable these settings for the required software:

sys-libs/glibc debugsyms installsources

Remember to re-emerge the libc after setting the needed package.env variables:

root #emerge --ask --oneshot sys-libs/glibc

To get meaningful backtraces, users may need to build more packages (such as dependencies of the software being debugged) with the above environment. For local projects, programs should be built with -Og -ggdb3.

Refuses to launch with strlen error

It is possible that Valgrind refuses to launch with an error like so:

valgrind:  A must-be-redirected function                        
valgrind:  whose name matches the pattern:      strlen          
valgrind:  in an object with soname matching: 

In this case, add -fno-builtin-strlen to CFLAGS for sys-libs/glibc:

# Needed for Valgrind
CFLAGS="${CFLAGS} -fno-builtin-strlen"
sys-libs/glibc glibc-no-strlen

Unhandled instruction bytes

This could be a few different errors and Valgrind's own FAQ covers it. The most common reason for seeing this however is that Valgrind does not currently support AVX512. Users should try building glibc with -march=x86-64-v3 or similar.



root #emerge --ask --depclean --verbose dev-util/valgrind

See also

  • GDB — used to find runtime errors that normally involve memory corruption
  • AddressSanitizer — a compiler feature in GCC and Clang that is able to detect several memory access errors.
  • UndefinedBehaviorSanitizer — a compiler feature in GCC and Clang that is able to detect various forms of undefined behaviour (UB).

External resources


  1. Jan Kratochvil. Memory error checking in C and C++: Comparing Sanitizers and Valgrind, Red Hat Developer Blog, May 5th, 2021. Retrieved on January 26th, 2023.