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Rollup merge of #62296 - RalfJung:memalign, r=alexcrichton

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request at least ptr-size alignment from posix_memalign

Fixes https://github.com/rust-lang/rust/issues/62251
This commit is contained in:
Mazdak Farrokhzad 2019-07-06 02:37:59 +02:00 committed by GitHub
commit 3c4a6c8606
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2 changed files with 26 additions and 16 deletions
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32
src/liballoc/tests/heap.rs
View File

@ -1,6 +1,6 @@
use std::alloc::{Global, Alloc, Layout, System};
/// Issue #45955.
/// Issue #45955 and #62251.
#[test]
fn alloc_system_overaligned_request() {
check_overalign_requests(System)
@ -12,21 +12,23 @@ fn std_heap_overaligned_request() {
}
fn check_overalign_requests<T: Alloc>(mut allocator: T) {
let size = 8;
let align = 16; // greater than size
let iterations = 100;
unsafe {
let pointers: Vec<_> = (0..iterations).map(|_| {
allocator.alloc(Layout::from_size_align(size, align).unwrap()).unwrap()
}).collect();
for &ptr in &pointers {
assert_eq!((ptr.as_ptr() as usize) % align, 0,
"Got a pointer less aligned than requested")
}
for &align in &[4, 8, 16, 32] { // less than and bigger than `MIN_ALIGN`
for &size in &[align/2, align-1] { // size less than alignment
let iterations = 128;
unsafe {
let pointers: Vec<_> = (0..iterations).map(|_| {
allocator.alloc(Layout::from_size_align(size, align).unwrap()).unwrap()
}).collect();
for &ptr in &pointers {
assert_eq!((ptr.as_ptr() as usize) % align, 0,
"Got a pointer less aligned than requested")
}
// Clean up
for &ptr in &pointers {
allocator.dealloc(ptr, Layout::from_size_align(size, align).unwrap())
// Clean up
for &ptr in &pointers {
allocator.dealloc(ptr, Layout::from_size_align(size, align).unwrap())
}
}
}
}
}

10
src/libstd/sys/unix/alloc.rs
View File

@ -6,6 +6,10 @@ use crate::alloc::{GlobalAlloc, Layout, System};
unsafe impl GlobalAlloc for System {
#[inline]
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
// jemalloc provides alignment less than MIN_ALIGN for small allocations.
// So only rely on MIN_ALIGN if size >= align.
// Also see <https://github.com/rust-lang/rust/issues/45955> and
// <https://github.com/rust-lang/rust/issues/62251#issuecomment-507580914>.
if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
libc::malloc(layout.size()) as *mut u8
} else {
@ -21,6 +25,7 @@ unsafe impl GlobalAlloc for System {
#[inline]
unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
// See the comment above in `alloc` for why this check looks the way it does.
if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
libc::calloc(layout.size(), 1) as *mut u8
} else {
@ -80,7 +85,10 @@ unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
#[inline]
unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
let mut out = ptr::null_mut();
let ret = libc::posix_memalign(&mut out, layout.align(), layout.size());
// posix_memalign requires 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 ret = libc::posix_memalign(&mut out, align, layout.size());
if ret != 0 {
ptr::null_mut()
} else {