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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/104633] [12 Regression] -Winfinite-recursion diagnoses
 fortify wrappers
Date: Tue, 22 Feb 2022 11:16:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104633

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #2)
> The following is a valid use of extern inline I think
>=20
> extern int memcmp (const void * p, const void *q, unsigned long size);
>=20
> extern inline __attribute__((always_inline,gnu_inline))
> int memcmp (const void * p, const void *q, unsigned long size)
> {
>   return memcmp (p, q, size);
> }

I think the above isn't actually valid, the compiler should still inline it
infinitely.  This is an infinite recursion.
extern inline __attribute__((always_inline,gnu_inline))
int memcmp (const void * p, const void *q, unsigned long size)
{
  return __builtin_memcmp (p, q, size);
}
is ok, __builtin_memcmp there doesn't mean it should use the user memcmp
inline, it should handle it as the builtin and if it decides it wants to ca=
ll,
will call memcmp (but the out of line one).

What glibc uses are either the call __builtin_whatever forms, or call an al=
ias,
say:
extern int __memcmp_alias (const void *, const void *, unsigned long) __asm
("memcmp");

extern inline __attribute__((always_inline,gnu_inline))
int memcmp (const void * p, const void *q, unsigned long size)
{
  return __memcmp_alias (p, q, size);
}
This one is also fine, it should call the external function, not the inline
recursively.
So, -Winfinite-recursion shouldn't warn about these 2 forms and should warn
about the #c2 case.=