Rollup merge of #62296 - RalfJung:memalign, r=alexcrichton
request at least ptr-size alignment from posix_memalign Fixes https://github.com/rust-lang/rust/issues/62251
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3c4a6c8606
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@ -1,6 +1,6 @@
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use std::alloc::{Global, Alloc, Layout, System};
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/// Issue #45955.
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/// Issue #45955 and #62251.
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#[test]
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fn alloc_system_overaligned_request() {
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check_overalign_requests(System)
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@ -12,9 +12,9 @@ fn std_heap_overaligned_request() {
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}
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fn check_overalign_requests<T: Alloc>(mut allocator: T) {
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let size = 8;
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let align = 16; // greater than size
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let iterations = 100;
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for &align in &[4, 8, 16, 32] { // less than and bigger than `MIN_ALIGN`
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for &size in &[align/2, align-1] { // size less than alignment
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let iterations = 128;
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unsafe {
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let pointers: Vec<_> = (0..iterations).map(|_| {
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allocator.alloc(Layout::from_size_align(size, align).unwrap()).unwrap()
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@ -29,4 +29,6 @@ fn check_overalign_requests<T: Alloc>(mut allocator: T) {
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allocator.dealloc(ptr, Layout::from_size_align(size, align).unwrap())
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}
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}
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}
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}
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}
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@ -6,6 +6,10 @@ use crate::alloc::{GlobalAlloc, Layout, System};
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unsafe impl GlobalAlloc for System {
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#[inline]
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unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
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// jemalloc provides alignment less than MIN_ALIGN for small allocations.
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// So only rely on MIN_ALIGN if size >= align.
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// Also see <https://github.com/rust-lang/rust/issues/45955> and
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// <https://github.com/rust-lang/rust/issues/62251#issuecomment-507580914>.
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if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
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libc::malloc(layout.size()) as *mut u8
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} else {
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@ -21,6 +25,7 @@ unsafe impl GlobalAlloc for System {
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#[inline]
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unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
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// See the comment above in `alloc` for why this check looks the way it does.
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if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
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libc::calloc(layout.size(), 1) as *mut u8
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} else {
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@ -80,7 +85,10 @@ unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
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#[inline]
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unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
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let mut out = ptr::null_mut();
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let ret = libc::posix_memalign(&mut out, layout.align(), layout.size());
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// posix_memalign requires that the alignment be a multiple of `sizeof(void*)`.
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// Since these are all powers of 2, we can just use max.
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let align = layout.align().max(crate::mem::size_of::<usize>());
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let ret = libc::posix_memalign(&mut out, align, layout.size());
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if ret != 0 {
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ptr::null_mut()
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} else {
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