From 5cc020d3df393ff0ba3a209a3f791f8823abf5cf Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Tue, 14 May 2024 19:32:11 +0200 Subject: [PATCH] avoid using aligned_alloc; posix_memalign is better-behaved --- library/std/src/sys/pal/unix/alloc.rs | 19 ++++++++----------- 1 file changed, 8 insertions(+), 11 deletions(-) diff --git a/library/std/src/sys/pal/unix/alloc.rs b/library/std/src/sys/pal/unix/alloc.rs index 9938c0bac25..d1e19329025 100644 --- a/library/std/src/sys/pal/unix/alloc.rs +++ b/library/std/src/sys/pal/unix/alloc.rs @@ -89,21 +89,18 @@ cfg_if::cfg_if! { // /memory/aligned_memory.cc 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 { #[inline] unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 { let mut out = ptr::null_mut(); - // posix_memalign requires that the alignment be a multiple of `sizeof(void*)`. - // Since these are all powers of 2, we can just use max. + // 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. + // 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::()); let ret = libc::posix_memalign(&mut out, align, layout.size()); if ret != 0 { ptr::null_mut() } else { out as *mut u8 }