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From: "pageexec at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ipa/96503] attribute alloc_size effect lost after inlining
Date: Fri, 18 Nov 2022 23:57:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96503

PaX Team <pageexec at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pageexec at gmail dot com

--- Comment #2 from Siddhesh Poyarekar <siddhesh at gcc dot gnu.org> ---
(In reply to Kees Cook from comment #1)
> Created attachment 53643 [details]
> PoC showing unexpected __bdos results across inlines
>=20
> Fixing this is needed for the Linux kernel to do much useful with
> alloc_size. Most of the allocators are inline wrappers, for example.

For cases where the size doesn't really change across the inlines, it ought=
 to
be sufficient to annotate the non-inlined implementation function, e.g. in =
case
of kvmalloc, annotate kvmalloc_node as __alloc_size(1).

For other cases it may be less trivial, e.g.:

/* Some padding the wrapper adds to the actual allocation.  */
size_t metadata_size;

__attribute__ ((alloc_size (1))) void *alloc_wrapper (size_t sz)
{
  return real_alloc (size + metadata_size);
}

extern void *real_alloc (size_t) __attribute__ ((alloc_size(1)));

here the compiler will end up seeing the padded size, which may not be corr=
ect.

To fix this we'll have to store the alloc_size info somewhere (ptr_info see=
ms
to be aliasing-specific, so maybe a new member to tree_ssa_name) during
inlining and then teach the tree-object-size pass to access it.=