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| author | Jonathan Wakely <jwakely@redhat.com> | 2021-10-06 20:05:48 +0100 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2021-10-21 00:19:20 +0100 |
| commit | 8a9a59311551e833ca064de44ac23b193e1b704d (patch) | |
| tree | 1d91ec3b267277e45d849261406337c1c4fa5a3f /misc | |
| parent | aa783f9a7b774d67487daa9376095738aef5cf88 (diff) | |
| download | glibc-8a9a59311551e833ca064de44ac23b193e1b704d.zip glibc-8a9a59311551e833ca064de44ac23b193e1b704d.tar.gz glibc-8a9a59311551e833ca064de44ac23b193e1b704d.tar.bz2 | |
Add alloc_align attribute to memalign et al
GCC 4.9.0 added the alloc_align attribute to say that a function
argument specifies the alignment of the returned pointer. Clang supports
the attribute too. Using the attribute can allow a compiler to generate
better code if it knows the returned pointer has a minimum alignment.
See https://gcc.gnu.org/PR60092 for more details.
GCC implicitly knows the semantics of aligned_alloc and posix_memalign,
but not the obsolete memalign. As a result, GCC generates worse code
when memalign is used, compared to aligned_alloc. Clang knows about
aligned_alloc and memalign, but not posix_memalign.
This change adds a new __attribute_alloc_align__ macro to <sys/cdefs.h>
and then uses it on memalign (where it helps GCC) and aligned_alloc
(where GCC and Clang already know the semantics, but it doesn't hurt)
and xposix_memalign. It can't be used on posix_memalign because that
doesn't return a pointer (the allocated pointer is returned via a void**
parameter instead).
Unlike the alloc_size attribute, alloc_align only allows a single
argument. That means the new __attribute_alloc_align__ macro doesn't
really need to be used with double parentheses to protect a comma
between its arguments. For consistency with __attribute_alloc_size__
this patch defines it the same way, so that double parentheses are
required.
Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>
Diffstat (limited to 'misc')
| -rw-r--r-- | misc/sys/cdefs.h | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h index c353d2e..ab57d4a 100644 --- a/misc/sys/cdefs.h +++ b/misc/sys/cdefs.h @@ -1,4 +1,5 @@ /* Copyright (C) 1992-2021 Free Software Foundation, Inc. + Copyright The GNU Toolchain Authors. This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or @@ -290,6 +291,15 @@ # define __attribute_alloc_size__(params) /* Ignore. */ #endif +/* Tell the compiler which argument to an allocation function + indicates the alignment of the allocation. */ +#if __GNUC_PREREQ (4, 9) || __glibc_has_attribute (__alloc_align__) +# define __attribute_alloc_align__(param) \ + __attribute__ ((__alloc_align__ param)) +#else +# define __attribute_alloc_align__(param) /* Ignore. */ +#endif + /* At some point during the gcc 2.96 development the `pure' attribute for functions was introduced. We don't want to use it unconditionally (although this would be possible) since it generates warnings. */ |