Upgrade to valgrind 3.12.0.
Release 3.12.0 (20 October 2016)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3.12.0 is a feature release with many improvements and the usual
collection of bug fixes.
This release supports X86/Linux, AMD64/Linux, ARM32/Linux,
ARM64/Linux, PPC32/Linux, PPC64BE/Linux, PPC64LE/Linux, S390X/Linux,
MIPS32/Linux, MIPS64/Linux, ARM/Android, ARM64/Android,
MIPS32/Android, X86/Android, X86/Solaris, AMD64/Solaris, X86/MacOSX
10.10 and AMD64/MacOSX 10.10. There is also preliminary support for
X86/MacOSX 10.11/12, AMD64/MacOSX 10.11/12 and TILEGX/Linux.
* ================== PLATFORM CHANGES =================
* POWER: Support for ISA 3.0 has been added
* mips: support for O32 FPXX ABI has been added.
* mips: improved recognition of different processors
* mips: determination of page size now done at run time
* amd64: Partial support for AMD FMA4 instructions.
* arm, arm64: Support for v8 crypto and CRC instructions.
* Improvements and robustification of the Solaris port.
* Preliminary support for MacOS 10.12 (Sierra) has been added.
Whilst 3.12.0 continues to support the 32-bit x86 instruction set, we
would prefer users to migrate to 64-bit x86 (a.k.a amd64 or x86_64)
where possible. Valgrind's support for 32-bit x86 has stagnated in
recent years and has fallen far behind that for 64-bit x86
instructions. By contrast 64-bit x86 is well supported, up to and
including AVX2.
* ==================== TOOL CHANGES ====================
* Memcheck:
- Added meta mempool support for describing a custom allocator which:
- Auto-frees all chunks assuming that destroying a pool destroys all
objects in the pool
- Uses itself to allocate other memory blocks
- New flag --ignore-range-below-sp to ignore memory accesses below
the stack pointer, if you really have to. The related flag
--workaround-gcc296-bugs=yes is now deprecated. Use
--ignore-range-below-sp=1024-1 as a replacement.
* DRD:
- Improved thread startup time significantly on non-Linux platforms.
* DHAT
- Added collection of the metric "tot-blocks-allocd"
* ==================== OTHER CHANGES ====================
* Replacement/wrapping of malloc/new related functions is now done not just
for system libraries by default, but for any globally defined malloc/new
related function (both in shared libraries and statically linked alternative
malloc implementations). The dynamic (runtime) linker is excluded, though.
To only intercept malloc/new related functions in
system libraries use --soname-synonyms=somalloc=nouserintercepts (where
"nouserintercepts" can be any non-existing library name).
This new functionality is not implemented for MacOS X.
* The maximum number of callers in a suppression entry is now equal to
the maximum size for --num-callers (500).
Note that --gen-suppressions=yes|all similarly generates suppressions
containing up to --num-callers frames.
* New and modified GDB server monitor features:
- Valgrind's gdbserver now accepts the command 'catch syscall'.
Note that you must have GDB >= 7.11 to use 'catch syscall' with
gdbserver.
* New option --run-cxx-freeres=<yes|no> can be used to change whether
__gnu_cxx::__freeres() cleanup function is called or not. Default is
'yes'.
* Valgrind is able to read compressed debuginfo sections in two formats:
- zlib ELF gABI format with SHF_COMPRESSED flag (gcc option -gz=zlib)
- zlib GNU format with .zdebug sections (gcc option -gz=zlib-gnu)
* Modest JIT-cost improvements: the cost of instrumenting code blocks
for the most common use case (x86_64-linux, Memcheck) has been
reduced by 10%-15%.
* Improved performance for programs that do a lot of discarding of
instruction address ranges of 8KB or less.
* The C++ symbol demangler has been updated.
* More robustness against invalid syscall parameters on Linux.
* ==================== FIXED BUGS ====================
The following bugs have been fixed or resolved. Note that "n-i-bz"
stands for "not in bugzilla" -- that is, a bug that was reported to us
but never got a bugzilla entry. We encourage you to file bugs in
bugzilla (https://bugs.kde.org/enter_bug.cgi?product=valgrind) rather
than mailing the developers (or mailing lists) directly -- bugs that
are not entered into bugzilla tend to get forgotten about or ignored.
To see details of a given bug, visit
https://bugs.kde.org/show_bug.cgi?id=XXXXXX
where XXXXXX is the bug number as listed below.
191069 Exiting due to signal not reported in XML output
199468 Suppressions: stack size limited to 25
while --num-callers allows more frames
212352 vex amd64 unhandled opc_aux = 0x 2, first_opcode == 0xDC (FCOM)
278744 cvtps2pd with redundant RexW
303877 valgrind doesn't support compressed debuginfo sections.
345307 Warning about "still reachable" memory when using libstdc++ from gcc 5
348345 Assertion fails for negative lineno
351282 V 3.10.1 MIPS softfloat build broken with GCC 4.9.3 / binutils 2.25.1
351692 Dumps created by valgrind are not readable by gdb (mips32 specific)
351804 Crash on generating suppressions for "printf" call on OS X 10.10
352197 mips: mmap2() not wrapped correctly for page size > 4096
353083 arm64 doesn't implement various xattr system calls
353084 arm64 doesn't support sigpending system call
353137 www: update info for Supported Platforms
353138 www: update "The Valgrind Developers" page
353370 don't advertise RDRAND in cpuid for Core-i7-4910-like avx2 machine
== 365325
== 357873
353384 amd64->IR: 0x66 0xF 0x3A 0x62 0xD1 0x62 (pcmpXstrX $0x62)
353398 WARNING: unhandled amd64-solaris syscall: 207
353660 XML in auxwhat tag not escaping reserved symbols properly
353680 s390x: Crash with certain glibc versions due to non-implemented TBEGIN
353727 amd64->IR: 0x66 0xF 0x3A 0x62 0xD1 0x72 (pcmpXstrX $0x72)
353802 ELF debug info reader confused with multiple .rodata sections
353891 Assert 'bad_scanned_addr < VG_ROUNDDN(start+len, sizeof(Addr))' failed
353917 unhandled amd64-solaris syscall fchdir(120)
353920 unhandled amd64-solaris syscall: 170
354274 arm: unhandled instruction: 0xEBAD 0x0AC1 (sub.w sl, sp, r1, lsl #3)
354392 unhandled amd64-solaris syscall: 171
354797 Vbit test does not include Iops for Power 8 instruction support
354883 tst->os_state.pthread - magic_delta assertion failure on OSX 10.11
== 361351
== 362920
== 366222
354933 Fix documentation of --kernel-variant=android-no-hw-tls option
355188 valgrind should intercept all malloc related global functions
355454 do not intercept malloc related symbols from the runtime linker
355455 stderr.exp of test cases wrapmalloc and wrapmallocstatic overconstrained
356044 Dwarf line info reader misinterprets is_stmt register
356112 mips: replace addi with addiu
356393 valgrind (vex) crashes because isZeroU happened
== 363497
== 364497
356676 arm64-linux: unhandled syscalls 125, 126 (sched_get_priority_max/min)
356678 arm64-linux: unhandled syscall 232 (mincore)
356817 valgrind.h triggers compiler errors on MSVC when defining NVALGRIND
356823 Unsupported ARM instruction: stlex
357059 x86/amd64: SSE cvtpi2ps with memory source does transition to MMX state
357338 Unhandled instruction for SHA instructions libcrypto Boring SSL
357673 crash if I try to run valgrind with a binary link with libcurl
357833 Setting RLIMIT_DATA to zero breaks with linux 4.5+
357871 pthread_spin_destroy not properly wrapped
357887 Calls to VG_(fclose) do not close the file descriptor
357932 amd64->IR: accept redundant REX prefixes for {minsd,maxsd} m128, xmm.
358030 support direct socket calls on x86 32bit (new in linux 4.3)
358478 drd/tests/std_thread.cpp doesn't build with GCC6
359133 Assertion 'eltSzB <= ddpa->poolSzB' failed
359181 Buffer Overflow during Demangling
359201 futex syscall "skips" argument 5 if op is FUTEX_WAIT_BITSET
359289 s390x: popcnt (B9E1) not implemented
359472 The Power PC vsubuqm instruction doesn't always give the correct result
359503 Add missing syscalls for aarch64 (arm64)
359645 "You need libc6-dbg" help message could be more helpful
359703 s390: wire up separate socketcalls system calls
359724 getsockname might crash - deref_UInt should call safe_to_deref
359733 amd64 implement ld.so strchr/index override like x86
359767 Valgrind does not support the IBM POWER ISA 3.0 instructions, part 1/5
359829 Power PC test suite none/tests/ppc64/test_isa_2_07.c uses
uninitialized data
359838 arm64: Unhandled instruction 0xD5033F5F (clrex)
359871 Incorrect mask handling in ppoll
359952 Unrecognised PCMPESTRM variants (0x70, 0x19)
360008 Contents of Power vr registers contents is not printed correctly when
the --vgdb-shadow-registers=yes option is used
360035 POWER PC instruction bcdadd and bcdsubtract generate result with
non-zero shadow bits
360378 arm64: Unhandled instruction 0x5E280844 (sha1h s4, s2)
360425 arm64 unsupported instruction ldpsw
== 364435
360519 none/tests/arm64/memory.vgtest might fail with newer gcc
360571 Error about the Android Runtime reading below the stack pointer on ARM
360574 Wrong parameter type for an ashmem ioctl() call on Android and ARM64
360749 kludge for multiple .rodata sections on Solaris no longer needed
360752 raise the number of reserved fds in m_main.c from 10 to 12
361207 Valgrind does not support the IBM POWER ISA 3.0 instructions, part 2/5
361226 s390x: risbgn (EC59) not implemented
361253 [s390x] ex_clone.c:42: undefined reference to `pthread_create'
361354 ppc64[le]: wire up separate socketcalls system calls
361615 Inconsistent termination for multithreaded process terminated by signal
361926 Unhandled Solaris syscall: sysfs(84)
362009 V dumps core on unimplemented functionality before threads are created
362329 Valgrind does not support the IBM POWER ISA 3.0 instructions, part 3/5
362894 missing (broken) support for wbit field on mtfsfi instruction (ppc64)
362935 [AsusWRT] Assertion 'sizeof(TTEntryC) <= 88' failed
362953 Request for an update to the Valgrind Developers page
363680 add renameat2() support
363705 arm64 missing syscall name_to_handle_at and open_by_handle_at
363714 ppc64 missing syscalls sync, waitid and name_to/open_by_handle_at
363858 Valgrind does not support the IBM POWER ISA 3.0 instructions, part 4/5
364058 clarify in manual limitations of array overruns detections
364413 pselect sycallwrapper mishandles NULL sigmask
364728 Power PC, missing support for several HW registers in
get_otrack_shadow_offset_wrk()
364948 Valgrind does not support the IBM POWER ISA 3.0 instructions, part 5/5
365273 Invalid write to stack location reported after signal handler runs
365912 ppc64BE segfault during jm-insns test (RELRO)
366079 FPXX Support for MIPS32 Valgrind
366138 Fix configure errors out when using Xcode 8 (clang 8.0.0)
366344 Multiple unhandled instruction for Aarch64
(0x0EE0E020, 0x1AC15800, 0x4E284801, 0x5E040023, 0x5E056060)
367995 Integration of memcheck with custom memory allocator
368120 x86_linux asm _start functions do not keep 16-byte aligned stack pointer
368412 False positive result for altivec capability check
368416 Add tc06_two_races_xml.exp output for ppc64
368419 Perf Events ioctls not implemented
368461 mmapunmap test fails on ppc64
368823 run_a_thread_NORETURN assembly code typo for VGP_arm64_linux target
369000 AMD64 fma4 instructions unsupported.
369169 ppc64 fails jm_int_isa_2_07 test
369175 jm_vec_isa_2_07 test crashes on ppc64
369209 valgrind loops and eats up all memory if cwd doesn't exist.
369356 pre_mem_read_sockaddr syscall wrapper can crash with bad sockaddr
369359 msghdr_foreachfield can crash when handling bad iovec
369360 Bad sigprocmask old or new sets can crash valgrind
369361 vmsplice syscall wrapper crashes on bad iovec
369362 Bad sigaction arguments crash valgrind
369383 x86 sys_modify_ldt wrapper crashes on bad ptr
369402 Bad set/get_thread_area pointer crashes valgrind
369441 bad lvec argument crashes process_vm_readv/writev syscall wrappers
369446 valgrind crashes on unknown fcntl command
369439 S390x: Unhandled insns RISBLG/RISBHG and LDE/LDER
369468 Remove quadratic metapool algorithm using VG_(HT_remove_at_Iter)
370265 ISA 3.0 HW cap stuff needs updating
371128 BCD add and subtract instructions on Power BE in 32-bit mode do not work
n-i-bz Fix incorrect (or infinite loop) unwind on RHEL7 x86 and amd64
n-i-bz massif --pages-as-heap=yes does not report peak caused by mmap+munmap
n-i-bz false positive leaks due to aspacemgr merging heap & non heap segments
n-i-bz Fix ppoll_alarm exclusion on OS X
n-i-bz Document brk segment limitation, reference manual in limit reached msg.
n-i-bz Fix clobber list in none/tests/amd64/xacq_xrel.c [valgrind r15737]
n-i-bz Bump allowed shift value for "add.w reg, sp, reg, lsl #N" [vex r3206]
n-i-bz amd64: memcheck false positive with shr %edx
n-i-bz arm3: Allow early writeback of SP base register in "strd rD, [sp, #-16]"
n-i-bz ppc: Fix two cases of PPCAvFpOp vs PPCFpOp enum confusion
n-i-bz arm: Fix incorrect register-number constraint check for LDAEX{,B,H,D}
n-i-bz DHAT: added collection of the metric "tot-blocks-allocd"
(3.12.0.RC1: 20 October 2016, vex r3282, valgrind r16094)
(3.12.0.RC2: 20 October 2016, vex r3282, valgrind r16096)
(3.12.0: 21 October 2016, vex r3282, valgrind r16098)
Bug: http://b/37470713
Bug: http://b/29251682
Test: ran runtests-arm(64)?.sh and the bug reporter's specific binary (32- and 64-bit)
Change-Id: I43ccbea946d89fc4ae9f355181ac5061d6ce4453
diff --git a/FAQ.txt b/FAQ.txt
new file mode 100644
index 0000000..2ffc052
--- /dev/null
+++ b/FAQ.txt
@@ -0,0 +1,456 @@
+
+
+Valgrind FAQ
+Release 3.12.0 20 October 2016
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Table of Contents
+1. Background
+2. Compiling, installing and configuring
+3. Valgrind aborts unexpectedly
+4. Valgrind behaves unexpectedly
+5. Miscellaneous
+6. How To Get Further Assistance
+
+------------------------------------------------------------------------
+1. Background
+------------------------------------------------------------------------
+
+1.1. How do you pronounce "Valgrind"?
+The "Val" as in the word "value". The "grind" is pronounced with a short
+'i' -- ie. "grinned" (rhymes with "tinned") rather than "grined" (rhymes
+with "find").
+
+Don't feel bad: almost everyone gets it wrong at first.
+------------------------------------------------------------------------
+
+1.2. Where does the name "Valgrind" come from?
+From Nordic mythology. Originally (before release) the project was named
+Heimdall, after the watchman of the Nordic gods. He could "see a hundred
+miles by day or night, hear the grass growing, see the wool growing on a
+sheep's back", etc. This would have been a great name, but it was
+already taken by a security package "Heimdal".
+
+Keeping with the Nordic theme, Valgrind was chosen. Valgrind is the name
+of the main entrance to Valhalla (the Hall of the Chosen Slain in
+Asgard). Over this entrance there resides a wolf and over it there is
+the head of a boar and on it perches a huge eagle, whose eyes can see to
+the far regions of the nine worlds. Only those judged worthy by the
+guardians are allowed to pass through Valgrind. All others are refused
+entrance.
+
+It's not short for "value grinder", although that's not a bad guess.
+
+------------------------------------------------------------------------
+2. Compiling, installing and configuring
+------------------------------------------------------------------------
+
+2.1. When building Valgrind, 'make' dies partway with an assertion
+failure, something like this:
+
+ % make: expand.c:489: allocated_variable_append:
+ Assertion 'current_variable_set_list->next != 0' failed.
+
+It's probably a bug in 'make'. Some, but not all, instances of version
+3.79.1 have this bug, see this:
+<http://www.mail-archive.com/bug-make@gnu.org/msg01658.html>. Try
+upgrading to a more recent version of 'make'. Alternatively, we have
+heard that unsetting the CFLAGS environment variable avoids the problem.
+
+------------------------------------------------------------------------
+
+2.2. When building Valgrind, 'make' fails with this:
+ /usr/bin/ld: cannot find -lc
+ collect2: ld returned 1 exit status
+
+You need to install the glibc-static-devel package.
+
+------------------------------------------------------------------------
+3. Valgrind aborts unexpectedly
+------------------------------------------------------------------------
+
+3.1. Programs run OK on Valgrind, but at exit produce a bunch of errors
+involving __libc_freeres and then die with a segmentation fault.
+
+When the program exits, Valgrind runs the procedure __libc_freeres in
+glibc. This is a hook for memory debuggers, so they can ask glibc to
+free up any memory it has used. Doing that is needed to ensure that
+Valgrind doesn't incorrectly report space leaks in glibc.
+
+The problem is that running __libc_freeres in older glibc versions
+causes this crash.
+
+Workaround for 1.1.X and later versions of Valgrind: use the
+--run-libc-freeres=no option. You may then get space leak reports for
+glibc allocations (please don't report these to the glibc people, since
+they are not real leaks), but at least the program runs.
+
+------------------------------------------------------------------------
+
+3.2. My (buggy) program dies like this:
+ valgrind: m_mallocfree.c:248 (get_bszB_as_is): Assertion 'bszB_lo == bszB_hi' failed.
+
+or like this:
+ valgrind: m_mallocfree.c:442 (mk_inuse_bszB): Assertion 'bszB != 0' failed.
+
+or otherwise aborts or crashes in m_mallocfree.c.
+If Memcheck (the memory checker) shows any invalid reads, invalid writes
+or invalid frees in your program, the above may happen. Reason is that
+your program may trash Valgrind's low-level memory manager, which then
+dies with the above assertion, or something similar. The cure is to fix
+your program so that it doesn't do any illegal memory accesses. The
+above failure will hopefully go away after that.
+
+------------------------------------------------------------------------
+
+3.3. My program dies, printing a message like this along the way:
+ vex x86->IR: unhandled instruction bytes: 0x66 0xF 0x2E 0x5
+
+One possibility is that your program has a bug and erroneously jumps to
+a non-code address, in which case you'll get a SIGILL signal. Memcheck
+may issue a warning just before this happens, but it might not if the
+jump happens to land in addressable memory.
+
+Another possibility is that Valgrind does not handle the instruction. If
+you are using an older Valgrind, a newer version might handle the
+instruction. However, all instruction sets have some obscure, rarely
+used instructions. Also, on amd64 there are an almost limitless number
+of combinations of redundant instruction prefixes, many of them
+undocumented but accepted by CPUs. So Valgrind will still have decoding
+failures from time to time. If this happens, please file a bug report.
+
+------------------------------------------------------------------------
+
+3.4. I tried running a Java program (or another program that uses a
+just-in-time compiler) under Valgrind but something went wrong. Does
+Valgrind handle such programs?
+
+Valgrind can handle dynamically generated code, so long as none of the
+generated code is later overwritten by other generated code. If this
+happens, though, things will go wrong as Valgrind will continue running
+its translations of the old code (this is true on x86 and amd64, on
+PowerPC there are explicit cache flush instructions which Valgrind
+detects and honours). You should try running with --smc-check=all in
+this case. Valgrind will run much more slowly, but should detect the use
+of the out-of-date code.
+
+Alternatively, if you have the source code to the JIT compiler you can
+insert calls to the VALGRIND_DISCARD_TRANSLATIONS client request to mark
+out-of-date code, saving you from using --smc-check=all.
+
+Apart from this, in theory Valgrind can run any Java program just fine,
+even those that use JNI and are partially implemented in other languages
+like C and C++. In practice, Java implementations tend to do nasty
+things that most programs do not, and Valgrind sometimes falls over
+these corner cases.
+
+If your Java programs do not run under Valgrind, even with
+--smc-check=all, please file a bug report and hopefully we'll be able to
+fix the problem.
+
+
+------------------------------------------------------------------------
+4. Valgrind behaves unexpectedly
+------------------------------------------------------------------------
+
+4.1. My program uses the C++ STL and string classes. Valgrind reports
+'still reachable' memory leaks involving these classes at the exit of
+the program, but there should be none.
+
+First of all: relax, it's probably not a bug, but a feature. Many
+implementations of the C++ standard libraries use their own memory pool
+allocators. Memory for quite a number of destructed objects is not
+immediately freed and given back to the OS, but kept in the pool(s) for
+later re-use. The fact that the pools are not freed at the exit of the
+program cause Valgrind to report this memory as still reachable. The
+behaviour not to free pools at the exit could be called a bug of the
+library though.
+
+Using GCC, you can force the STL to use malloc and to free memory as
+soon as possible by globally disabling memory caching. Beware! Doing so
+will probably slow down your program, sometimes drastically.
+
+* With GCC 2.91, 2.95, 3.0 and 3.1, compile all source using the STL
+with -D__USE_MALLOC. Beware! This was removed from GCC starting with
+version 3.3.
+
+* With GCC 3.2.2 and later, you should export the environment variable
+GLIBCPP_FORCE_NEW before running your program.
+
+* With GCC 3.4 and later, that variable has changed name to
+GLIBCXX_FORCE_NEW.
+
+There are other ways to disable memory pooling: using the malloc_alloc
+template with your objects (not portable, but should work for GCC) or
+even writing your own memory allocators. But all this goes beyond the
+scope of this FAQ. Start by reading
+http://gcc.gnu.org/onlinedocs/libstdc++/faq/index.html#4_4_leak:
+<http://gcc.gnu.org/onlinedocs/libstdc++/faq/index.html#4_4_leak> if you
+absolutely want to do that. But beware: allocators belong to the more
+messy parts of the STL and people went to great lengths to make the STL
+portable across platforms. Chances are good that your solution will work
+on your platform, but not on others.
+
+------------------------------------------------------------------------
+
+4.2. The stack traces given by Memcheck (or another tool) aren't
+helpful. How can I improve them?
+
+If they're not long enough, use --num-callers to make them longer.
+If they're not detailed enough, make sure you are compiling with -g to
+add debug information. And don't strip symbol tables (programs should be
+unstripped unless you run 'strip' on them; some libraries ship
+stripped).
+
+Also, for leak reports involving shared objects, if the shared object is
+unloaded before the program terminates, Valgrind will discard the debug
+information and the error message will be full of ??? entries. The
+workaround here is to avoid calling dlclose on these shared objects.
+
+Also, -fomit-frame-pointer and -fstack-check can make stack traces
+worse.
+
+Some example sub-traces:
+* With debug information and unstripped (best):
+ Invalid write of size 1
+ at 0x80483BF: really (malloc1.c:20)
+ by 0x8048370: main (malloc1.c:9)
+
+* With no debug information, unstripped:
+ Invalid write of size 1
+ at 0x80483BF: really (in /auto/homes/njn25/grind/head5/a.out)
+ by 0x8048370: main (in /auto/homes/njn25/grind/head5/a.out)
+
+* With no debug information, stripped:
+ Invalid write of size 1
+ at 0x80483BF: (within /auto/homes/njn25/grind/head5/a.out)
+ by 0x8048370: (within /auto/homes/njn25/grind/head5/a.out)
+ by 0x42015703: __libc_start_main (in /lib/tls/libc-2.3.2.so)
+ by 0x80482CC: (within /auto/homes/njn25/grind/head5/a.out)
+
+* With debug information and -fomit-frame-pointer:
+ Invalid write of size 1
+ at 0x80483C4: really (malloc1.c:20)
+ by 0x42015703: __libc_start_main (in /lib/tls/libc-2.3.2.so)
+ by 0x80482CC: ??? (start.S:81)
+
+* A leak error message involving an unloaded shared object:
+ 84 bytes in 1 blocks are possibly lost in loss record 488 of 713
+ at 0x1B9036DA: operator new(unsigned) (vg_replace_malloc.c:132)
+ by 0x1DB63EEB: ???
+ by 0x1DB4B800: ???
+ by 0x1D65E007: ???
+ by 0x8049EE6: main (main.cpp:24)
+
+------------------------------------------------------------------------
+
+4.3. The stack traces given by Memcheck (or another tool) seem to have
+the wrong function name in them. What's happening?
+
+Occasionally Valgrind stack traces get the wrong function names. This is
+caused by glibc using aliases to effectively give one function two
+names. Most of the time Valgrind chooses a suitable name, but very
+occasionally it gets it wrong. Examples we know of are printing bcmp
+instead of memcmp, index instead of strchr, and rindex instead of
+strrchr.
+
+------------------------------------------------------------------------
+
+4.4. My program crashes normally, but doesn't under Valgrind, or vice
+versa. What's happening?
+
+When a program runs under Valgrind, its environment is slightly
+different to when it runs natively. For example, the memory layout is
+different, and the way that threads are scheduled is different.
+
+Most of the time this doesn't make any difference, but it can,
+particularly if your program is buggy. For example, if your program
+crashes because it erroneously accesses memory that is unaddressable,
+it's possible that this memory will not be unaddressable when run under
+Valgrind. Alternatively, if your program has data races, these may not
+manifest under Valgrind.
+
+There isn't anything you can do to change this, it's just the nature of
+the way Valgrind works that it cannot exactly replicate a native
+execution environment. In the case where your program crashes due to a
+memory error when run natively but not when run under Valgrind, in most
+cases Memcheck should identify the bad memory operation.
+
+------------------------------------------------------------------------
+
+4.5. Memcheck doesn't report any errors and I know my program has
+errors.
+
+There are two possible causes of this.
+First, by default, Valgrind only traces the top-level process. So if
+your program spawns children, they won't be traced by Valgrind by
+default. Also, if your program is started by a shell script, Perl
+script, or something similar, Valgrind will trace the shell, or the Perl
+interpreter, or equivalent.
+
+To trace child processes, use the --trace-children=yes option.
+If you are tracing large trees of processes, it can be less disruptive
+to have the output sent over the network. Give Valgrind the option
+--log-socket=127.0.0.1:12345 (if you want logging output sent to port
+12345 on localhost). You can use the valgrind-listener program to listen
+on that port:
+
+ valgrind-listener 12345
+
+Obviously you have to start the listener process first. See the manual
+for more details.
+
+Second, if your program is statically linked, most Valgrind tools will
+only work well if they are able to replace certain functions, such as
+malloc, with their own versions. By default, statically linked malloc
+functions are not replaced. A key indicator of this is if Memcheck says:
+All heap blocks were freed -- no leaks are possible when you know your
+program calls malloc. The workaround is to use the option
+--soname-synonyms=somalloc=NONE or to avoid statically linking your
+program.
+
+There will also be no replacement if you use an alternative malloc
+library such as tcmalloc, jemalloc, ... In such a case, the option
+--soname-synonyms=somalloc=zzzz (where zzzz is the soname of the
+alternative malloc library) will allow Valgrind to replace the
+functions.
+
+------------------------------------------------------------------------
+
+4.6. Why doesn't Memcheck find the array overruns in this program?
+ int static[5];
+
+ int main(void)
+ {
+ int stack[5];
+
+ static[5] = 0;
+ stack [5] = 0;
+
+ return 0;
+ }
+
+Unfortunately, Memcheck doesn't do bounds checking on global or stack
+arrays. We'd like to, but it's just not possible to do in a reasonable
+way that fits with how Memcheck works. Sorry.
+
+However, the experimental tool SGcheck can detect errors like this. Run
+Valgrind with the --tool=exp-sgcheck option to try it, but be aware that
+it is not as robust as Memcheck.
+
+
+------------------------------------------------------------------------
+5. Miscellaneous
+------------------------------------------------------------------------
+
+5.1. I tried writing a suppression but it didn't work. Can you write my
+suppression for me?
+
+Yes! Use the --gen-suppressions=yes feature to spit out suppressions
+automatically for you. You can then edit them if you like, eg. combining
+similar automatically generated suppressions using wildcards like '*'.
+
+If you really want to write suppressions by hand, read the manual
+carefully. Note particularly that C++ function names must be mangled
+(that is, not demangled).
+
+------------------------------------------------------------------------
+
+5.2. With Memcheck's memory leak detector, what's the difference between
+"definitely lost", "indirectly lost", "possibly lost", "still
+reachable", and "suppressed"?
+
+The details are in the Memcheck section of the user manual.
+In short:
+* "definitely lost" means your program is leaking memory -- fix those
+leaks!
+
+* "indirectly lost" means your program is leaking memory in a
+pointer-based structure. (E.g. if the root node of a binary tree is
+"definitely lost", all the children will be "indirectly lost".) If you
+fix the "definitely lost" leaks, the "indirectly lost" leaks should go
+away.
+
+* "possibly lost" means your program is leaking memory, unless you're
+doing unusual things with pointers that could cause them to point into
+the middle of an allocated block; see the user manual for some possible
+causes. Use --show-possibly-lost=no if you don't want to see these
+reports.
+
+* "still reachable" means your program is probably ok -- it didn't free
+some memory it could have. This is quite common and often reasonable.
+Don't use --show-reachable=yes if you don't want to see these reports.
+
+* "suppressed" means that a leak error has been suppressed. There are
+some suppressions in the default suppression files. You can ignore
+suppressed errors.
+
+------------------------------------------------------------------------
+
+5.3. Memcheck's uninitialised value errors are hard to track down,
+because they are often reported some time after they are caused. Could
+Memcheck record a trail of operations to better link the cause to the
+effect? Or maybe just eagerly report any copies of uninitialised memory
+values?
+
+Prior to version 3.4.0, the answer was "we don't know how to do it
+without huge performance penalties". As of 3.4.0, try using the
+--track-origins=yes option. It will run slower than usual, but will give
+you extra information about the origin of uninitialised values.
+
+Or if you want to do it the old fashioned way, you can use the client
+request VALGRIND_CHECK_VALUE_IS_DEFINED to help track these errors down
+-- work backwards from the point where the uninitialised error occurs,
+checking suspect values until you find the cause. This requires editing,
+compiling and re-running your program multiple times, which is a pain,
+but still easier than debugging the problem without Memcheck's help.
+
+As for eager reporting of copies of uninitialised memory values, this
+has been suggested multiple times. Unfortunately, almost all programs
+legitimately copy uninitialised memory values around (because compilers
+pad structs to preserve alignment) and eager checking leads to hundreds
+of false positives. Therefore Memcheck does not support eager checking
+at this time.
+
+------------------------------------------------------------------------
+
+5.4. Is it possible to attach Valgrind to a program that is already
+running?
+
+No. The environment that Valgrind provides for running programs is
+significantly different to that for normal programs, e.g. due to
+different layout of memory. Therefore Valgrind has to have full control
+from the very start.
+
+It is possible to achieve something like this by running your program
+without any instrumentation (which involves a slow-down of about 5x,
+less than that of most tools), and then adding instrumentation once you
+get to a point of interest. Support for this must be provided by the
+tool, however, and Callgrind is the only tool that currently has such
+support. See the instructions on the callgrind_control program for
+details.
+
+
+------------------------------------------------------------------------
+6. How To Get Further Assistance
+------------------------------------------------------------------------
+
+Read the appropriate section(s) of the Valgrind Documentation:
+<http://www.valgrind.org/docs/manual/index.html>.
+
+Search: <http://search.gmane.org> the valgrind-users:
+<http://news.gmane.org/gmane.comp.debugging.valgrind> mailing list
+archives, using the group name gmane.comp.debugging.valgrind.
+
+If you think an answer in this FAQ is incomplete or inaccurate, please
+e-mail valgrind@valgrind.org: <valgrind@valgrind.org>.
+
+If you have tried all of these things and are still stuck, you can try
+mailing the valgrind-users mailing list:
+<http://www.valgrind.org/support/mailing_lists.html>. Note that an email
+has a better change of being answered usefully if it is clearly written.
+Also remember that, despite the fact that most of the community are very
+helpful and responsive to emailed questions, you are probably requesting
+help from unpaid volunteers, so you have no guarantee of receiving an
+answer.
+