Re: Valgrind '--show-leak-kinds=all'

[Richard Biener <richard.guenther@gmail.com>]

On August 6, 2021 4:09:37 PM GMT+02:00, Thomas Schwinge <thomas@codesourcery.com> wrote:
>Hi!
>
>I'm working on plugging a memory leak in an entirely different
>compartment of GCC, but also ran into this issue:
>
>On 2021-02-12T08:35:52+0100, Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>> On Thu, Feb 11, 2021 at 7:35 PM Martin Sebor <msebor@gmail.com> wrote:
>>> On 2/11/21 12:59 AM, Richard Biener wrote:
>>> > On Wed, Feb 10, 2021 at 6:16 PM Martin Sebor <msebor@gmail.com> wrote:
>>> >> [...] Valgrind shows more leaks in this code that
>>> >> I'm not sure what to do about:
>>> >>
>>> >> 1) A tree built by build_type_attribute_qual_variant() called from
>>> >>      attr_access::array_as_string() to build a temporary type only
>>> >>      for the purposes of formatting it.
>>> >>
>>> >> 2) A tree (an attribute list) built by tree_cons() called from
>>> >>      build_attr_access_from_parms() that's used only for the duration
>>> >>      of the caller.
>>> >>
>>> >> Do these temporary trees need to be released somehow or are the leaks
>>> >> expected?
>>> >
>>> > You should configure GCC with --enable-valgrind-annotations to make
>>> > it aware of our GC.
>>>
>>> I did configure with that option:
>>>
>>> $ /src/gcc/master/configure --enable-checking=yes
>>> --enable-languages=all,jit,lto --enable-host-shared
>>> --enable-valgrind-annotations
>
>>> $ /build/gcc-master/gcc/xgcc -B /build/gcc-master/gcc -S -Wall
>>> /src/gcc/master/gcc/testsuite/gcc.dg/Wvla-parameter.c -wrapper
>>> valgrind,--leak-check=full,--show-leak-kinds=all,--track-origins=yes,--log-file=valgrind-out.txt
>>>
>>> Do you not see the same leaks?
>
>I do; also stuff like:
>
>    56 bytes in 1 blocks are still reachable in loss record 152 of 875
>       at 0x483DD99: calloc (vg_replace_malloc.c:762)
>       by 0x1753240: xcalloc (xmalloc.c:162)
>       by 0x669C83: ggc_internal_alloc(unsigned long, void (*)(void*), unsigned long, unsigned long) (ggc-page.c:918)
>       by 0x89E07D: ggc_internal_cleared_alloc(unsigned long, void (*)(void*), unsigned long, unsigned long) (ggc-common.c:117)
>       by 0xF65D0D: make_node(tree_code) (ggc.h:143)
>       by 0xF6632B: build_decl(unsigned int, tree_code, tree_node*, tree_node*) (tree.c:5264)
>       by 0xA28ADC: build_builtin_function(unsigned int, char const*, tree_node*, int, built_in_class, char const*, tree_node*) (langhooks.c:681)
>       by 0xA29FDD: add_builtin_function(char const*, tree_node*, int, built_in_class, char const*, tree_node*) (langhooks.c:716)
>       by 0x622BFB: def_builtin_1(built_in_function, char const*, built_in_class, tree_node*, tree_node*, bool, bool, bool, tree_node*, bool) [clone .constprop.25] (lto-lang.c:650)
>       by 0x640709: lto_define_builtins(tree_node*, tree_node*) (omp-builtins.def:46)
>       by 0x641EE3: lto_init() (lto-lang.c:1339)
>       by 0x61E26A: toplev::main(int, char**) (toplev.c:1921)
>
>... and many, many more.
>
>> Err, well.  --show-leak-kinds=all is probably the cause.
>
>Before finding this email, I too had convinced myself that everying that
>came by 'ggc_*' I may ignore, because:
>
>> We
>> definitely do not force-release
>> all reachable GC allocated memory at program end.
>
>... of this: these blocks simply had not been GCed at program end.
>
>It's however a bit tedious to filter, in my case, 11864 lines of Valgrind
>output.
>
>> Not sure if
>> valgrind annotations can
>> make that obvious to valgrind.
>
>Or, if that's not feasible (I don't know much about Valgrind...), then
>instead would it help to force a final GC at program end if we're running
>in "valgrind mode"?  If that's a plausible thing to do, would guarding
>that by GCC having been configured with '--enable-valgrind-annotations'
>be OK, or do we need a '--param', or something else?

Well, instead of a final GC we could explicitly release all GC managed memory. 

>> I'm just using --leak-check=full and
>> thus look for
>> unreleased and no longer reachable memory.
>
>ACK, in my case, that only shows seven errors (not related to my stuff).
>
>
>Grüße
> Thomas
>-----------------
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