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Rollup merge of #125003 - RalfJung:aligned_alloc, r=cuviper

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avoid using aligned_alloc; posix_memalign is better-behaved

Also there's no reason why wasi should be different than all the other Unixes here.
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León Orell Valerian Liehr 2024-05-15 22:01:18 +02:00 committed by GitHub
commit c5b17ec9d2
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1 changed files with 8 additions and 11 deletions
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19
library/std/src/sys/pal/unix/alloc.rs
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@ -87,21 +87,18 @@ cfg_if::cfg_if! {
// /memory/aligned_memory.cc // /memory/aligned_memory.cc
libc::memalign(layout.align(), layout.size()) as *mut u8 libc::memalign(layout.align(), layout.size()) as *mut u8
} }
} else if #[cfg(target_os = "wasi")] {
#[inline]
unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
// C11 aligned_alloc requires that the size be a multiple of the alignment.
// Layout already checks that the size rounded up doesn't overflow isize::MAX.
let align = layout.align();
let size = layout.size().next_multiple_of(align);
libc::aligned_alloc(align, size) as *mut u8
}
} else { } else {
#[inline] #[inline]
unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 { unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
let mut out = ptr::null_mut(); let mut out = ptr::null_mut();
// posix_memalign requires that the alignment be a multiple of `sizeof(void*)`. // We prefer posix_memalign over aligned_malloc since with aligned_malloc,
// Since these are all powers of 2, we can just use max. // implementations are making almost arbitrary choices for which alignments are
// "supported", making it hard to use. For instance, some implementations require the
// size to be a multiple of the alignment (wasi emmalloc), while others require the
// alignment to be at least the pointer size (Illumos, macOS) -- which may or may not be
// standards-compliant, but that does not help us.
// posix_memalign only has one, clear requirement: that the alignment be a multiple of
// `sizeof(void*)`. Since these are all powers of 2, we can just use max.
let align = layout.align().max(crate::mem::size_of::<usize>()); let align = layout.align().max(crate::mem::size_of::<usize>());
let ret = libc::posix_memalign(&mut out, align, layout.size()); let ret = libc::posix_memalign(&mut out, align, layout.size());
if ret != 0 { ptr::null_mut() } else { out as *mut u8 } if ret != 0 { ptr::null_mut() } else { out as *mut u8 }