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use posix_memalign on almost all Unix targets #125271

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May 25, 2024
Merged

use posix_memalign on almost all Unix targets #125271

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e7772f2
use posix_memalign on most Unix targets
RalfJung May 19, 2024
3c2d9c2
fix typo
RalfJung May 19, 2024
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16 changes: 7 additions & 9 deletions library/std/src/sys/pal/unix/alloc.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -59,10 +59,9 @@ unsafe impl GlobalAlloc for System {
}

cfg_if::cfg_if! {
// We use posix_memalign wherever possible, but not all targets have that function.
// We use posix_memalign wherever possible, but some targets have very incomplete POSIX coverage
// so we need a fallback for those.
if #[cfg(any(
target_os = "redox",
target_os = "espidf",
target_os = "horizon",
target_os = "vita",
))] {
Expand All @@ -74,12 +73,11 @@ cfg_if::cfg_if! {
#[inline]
unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
let mut out = ptr::null_mut();
// We prefer posix_memalign over aligned_malloc since with aligned_malloc,
// 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.
// We prefer posix_memalign over aligned_malloc since it is more widely available, and
// since with aligned_malloc, implementations are making almost arbitrary choices for
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// 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).
// 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>());
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