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From: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug gcov-profile/97461] [11 Regression] allocate_gcov_kvp()
 deadlocks in firefox LTO+PGO build (overridden malloc() recursion)
Date: Mon, 19 Oct 2020 13:42:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97461

--- Comment #6 from Martin Li=C5=A1ka <marxin at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #5)
> Hmm, is the TOPN allocation strathegy configurable?  I wonder whether we =
have
> to resort to an alternate allocation scheme (mmap/sbrk), avoiding libc?

No. The only thing we support is a recursive malloc as seen in:
./gcc/testsuite/gcc.dg/tree-prof/indir-call-prof-malloc.c

It was added in g:bc2b1a232b1825b421a1aaa21a0865b2d1e4e08c as we use a
statically allocated buffer when we recursively entry allocate_gcov_kvp.

However this is different as we can't call malloc/calloc from the function =
as
we're in code that initializes a memory allocator.

We can mitigate the issue with a pair of new functions __gcov_supress_malloc
and __gcov_alloc_malloc that will be called by a custom memory allocator.

What do you think about it?

>  At
> least
> I don't see a good way to force the gcov allocation to call the libc mall=
oc
> rather than a user replacement that is being instrumented.  Of course the
> instrumentation code could do sth like
>=20
>   if (is_allocated =3D=3D 0)
>     {
>       is_allocated =3D in_progress;
>       ... =3D malloc ();
>       is_allocated =3D 1;
>     }
>   else if (is_allocted =3D=3D in_progress)
>     {
>       topn_mem =3D &transitional_garbage_space;
>     }
>=20
> but of course that's quite some overhead for a small benefit.  Maybe it
> could be hidden in gcov_malloc.=