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YJIT: No need to fill to get UDF on ARM64

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On ARM64, all zeros is already undefined, so we don't need to do extra
work to fill new memory with undefined instructions.
This commit is contained in:
Alan Wu 2022-10-12 16:19:55 -04:00
parent 2cc3963a00
commit 1b0c9d0e3d
Notes: git 2022-10-14 03:30:07 +09:00 
Merged: https://github.com/ruby/ruby/pull/6536
1 changed files with 11 additions and 4 deletions
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15
yjit/src/virtualmem.rs
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@ -141,10 +141,16 @@ impl<A: Allocator> VirtualMemory<A> {
if !alloc.mark_writable(mapped_region_end.cast(), alloc_size_u32) {
return Err(FailedPageMapping);
}
// Fill new memory with PUSH DS (0x1E) so that executing uninitialized memory
// will fault with #UD in 64-bit mode. On Linux it becomes SIGILL and use the
// usual Ruby crash reporter.
std::slice::from_raw_parts_mut(mapped_region_end, alloc_size).fill(0x1E);
if cfg!(target_arch = "x86_64") {
// Fill new memory with PUSH DS (0x1E) so that executing uninitialized memory
// will fault with #UD in 64-bit mode. On Linux it becomes SIGILL and use the
// usual Ruby crash reporter.
std::slice::from_raw_parts_mut(mapped_region_end, alloc_size).fill(0x1E);
} else if cfg!(target_arch = "aarch64") {
// In aarch64, all zeros encodes UDF, so it's already what we want.
} else {
unreachable!("unknown arch");
}
}
self.mapped_region_bytes = self.mapped_region_bytes + alloc_size;
@ -309,6 +315,7 @@ pub mod tests {
}
#[test]
#[cfg(target_arch = "x86_64")]
fn new_memory_is_initialized() {
let mut virt = new_dummy_virt_mem();