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fix: omit nomem option to prevent compiler reorderings #11

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fix: omit nomem option to prevent compiler reorderings #11

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28 changes: 13 additions & 15 deletions src/held_interrupts.rs
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Original file line number Diff line number Diff line change
@@ -1,9 +1,11 @@
// Originally inspired by Tifflin OS.

use core::{
arch::asm,
sync::atomic::{compiler_fence, Ordering},
};
// The assembly blocks intentionally omit the `nomem` option to prevent the
// compiler from reordering memory accesses across the block.
//
// See https://github.com/mkroening/interrupt-ref-cell/issues/5#issuecomment-1753047784.

use core::arch::asm;

/// A guard type for withholding regular interrupts on the current CPU.
///
Expand Down Expand Up @@ -45,17 +47,16 @@ impl Drop for HeldInterrupts {
/// use the [`enable_fast_interrupts()`] interrupts.
#[inline(always)]
pub fn enable_interrupts() {
compiler_fence(Ordering::SeqCst);
unsafe {
#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
asm!("sti", options(nomem, nostack));
asm!("sti", options(nostack, preserves_flags));

#[cfg(target_arch = "aarch64")]
// Clear the I bit, which is bit 1 of the DAIF bitset.
asm!("msr daifclr, #2", options(nomem, nostack, preserves_flags));
asm!("msr daifclr, #2", options(nostack, preserves_flags));

#[cfg(target_arch = "arm")]
asm!("cpsie i", options(nomem, nostack, preserves_flags));
asm!("cpsie i", options(nostack, preserves_flags));
}
}

Expand All @@ -68,16 +69,15 @@ pub fn enable_interrupts() {
pub fn disable_interrupts() {
unsafe {
#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
asm!("cli", options(nomem, nostack));
asm!("cli", options(nostack, preserves_flags));

#[cfg(target_arch = "aarch64")]
// Set the I bit, which is bit 1 of the DAIF bitset.
asm!("msr daifset, #2", options(nomem, nostack, preserves_flags));

#[cfg(target_arch = "arm")]
asm!("cpsid i", options(nomem, nostack, preserves_flags));
asm!("cpsid i", options(nostack, preserves_flags));
}
compiler_fence(Ordering::SeqCst);
}

/// Unconditionally enables fast interrupts (FIQs); aarch64-only.
Expand All @@ -87,10 +87,9 @@ pub fn disable_interrupts() {
#[inline(always)]
#[cfg(target_arch = "aarch64")]
pub fn enable_fast_interrupts() {
compiler_fence(Ordering::SeqCst);
unsafe {
// Clear the F bit, which is bit 0 of the DAIF bitset.
asm!("msr daifclr, #1", options(nomem, nostack, preserves_flags));
asm!("msr daifclr, #1", options(nostack, preserves_flags));
}
}

Expand All @@ -103,9 +102,8 @@ pub fn enable_fast_interrupts() {
pub fn disable_fast_interrupts() {
unsafe {
// Clear the F bit, which is bit 0 of the DAIF bitset.
asm!("msr daifset, #1", options(nomem, nostack, preserves_flags));
asm!("msr daifset, #1", options(nostack, preserves_flags));
}
compiler_fence(Ordering::SeqCst);
}

/// Returns whether regular interrupts are enabled on the current CPU.
Expand Down