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cursor: prevent llvm-opt inserting memcpy in r/w

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Simon Renblad 2024-11-19 15:17:06 +08:00
parent c0f508bb17
commit 1c739e81ab
1 changed files with 7 additions and 0 deletions
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7
src/libio/cursor.rs
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@ -1,6 +1,8 @@
#[cfg(feature = "alloc")] #[cfg(feature = "alloc")]
use alloc::vec::Vec; use alloc::vec::Vec;
use core::arch::asm;
use crate::{Read, Write}; use crate::{Read, Write};
#[derive(Debug, Clone)] #[derive(Debug, Clone)]
@ -49,6 +51,9 @@ impl<T: AsRef<[u8]>> Read for Cursor<T> {
let len = buf.len().min(data.len()); let len = buf.len().min(data.len());
// ``copy_from_slice`` generates AXI bursts, use a regular loop instead // ``copy_from_slice`` generates AXI bursts, use a regular loop instead
for i in 0..len { for i in 0..len {
// HACK: On opt-level=2 or above, LLVM 18 may insert memcpy calls as an optimization pass,
// causing AXI bursts.
unsafe { asm!("", options(preserves_flags, nostack, readonly)); }
buf[i] = data[i]; buf[i] = data[i];
} }
self.pos += len; self.pos += len;
@ -64,6 +69,8 @@ impl Write for Cursor<&mut [u8]> {
let data = &mut self.inner[self.pos..]; let data = &mut self.inner[self.pos..];
let len = buf.len().min(data.len()); let len = buf.len().min(data.len());
for i in 0..len { for i in 0..len {
// HACK: On opt-level=2 or above, this is too fast and sends corrupted packets.
unsafe { asm!("", options(preserves_flags, nostack, readonly)); }
data[i] = buf[i]; data[i] = buf[i];
} }
self.pos += len; self.pos += len;