From 8a9a59311551e833ca064de44ac23b193e1b704d Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Wed, 6 Oct 2021 20:05:48 +0100 Subject: 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 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 Reviewed-by: Carlos O'Donell Tested-by: Carlos O'Donell --- malloc/malloc.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'malloc') diff --git a/malloc/malloc.h b/malloc/malloc.h index 2df0b38..0e8a0cf 100644 --- a/malloc/malloc.h +++ b/malloc/malloc.h @@ -1,5 +1,6 @@ /* Prototypes and definition for malloc implementation. Copyright (C) 1996-2021 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 @@ -64,8 +65,8 @@ extern void free (void *__ptr) __THROW; /* Allocate SIZE bytes allocated to ALIGNMENT bytes. */ extern void *memalign (size_t __alignment, size_t __size) - __THROW __attribute_malloc__ __attribute_alloc_size__ ((2)) __wur - __attr_dealloc_free; + __THROW __attribute_malloc__ __attribute_alloc_align__ ((1)) + __attribute_alloc_size__ ((2)) __wur __attr_dealloc_free; /* Allocate SIZE bytes on a page boundary. */ extern void *valloc (size_t __size) __THROW __attribute_malloc__ -- cgit v1.1