From b53c1ae17ad396730c12bafdd745b04e2b170ed9 Mon Sep 17 00:00:00 2001
From: Tobias Decking <Tobias.Decking@gmail.com>
Date: Wed, 22 Feb 2023 00:07:41 +0100
Subject: [PATCH] Improve assembly quality + AT&T syntax.

---
 library/compiler-builtins/src/mem/x86_64.rs | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/library/compiler-builtins/src/mem/x86_64.rs b/library/compiler-builtins/src/mem/x86_64.rs
index 282074a6cbc4..fe93ae7aed4e 100644
--- a/library/compiler-builtins/src/mem/x86_64.rs
+++ b/library/compiler-builtins/src/mem/x86_64.rs
@@ -179,24 +179,25 @@ pub unsafe fn c_string_length(s: *const core::ffi::c_char) -> usize {
 
     asm!(
         // search for a zero byte
-        "xor al, al",
+        "xor %eax, %eax",
 
         // unbounded memory region
-        "xor rcx, rcx",
-        "not rcx",
+        "xor %ecx, %ecx",
+        "not %rcx",
 
         // forward direction
-        "cld",
+        // (already set thanks to abi)
+        //"cld",
 
         // perform search
-        "repne scasb",
+        "repne scasb (%rdi), %al",
 
         // extract length
-        "not rcx",
-        "dec rcx",
+        "not %rcx",
+        "dec %rcx",
         inout("rdi") s => _,
         out("rcx") n,
-        options(nostack),
+        options(att_syntax, nostack),
     );
 
     n