From 690fb140151b05e63f6f51a9e0cd231c0d9fd44f Mon Sep 17 00:00:00 2001
From: Cyan Ogilvie <cyan.ogilvie@gmail.com>
Date: Thu, 16 Apr 2026 10:22:00 -0300
Subject: [PATCH] x86_64-gen: fix missing REX prefix for xor zero into r8-r15

load() used a raw o() call to emit xor-zero which lost bit 3 of the
register number via REG_VALUE():

    o(0xc031 + REG_VALUE(r) * 0x900);

For r >= 8, this emitted the wrong instruction (e.g. xor %ebx,%ebx
for TREG_R11 instead of xor %r11d,%r11d), clobbering the wrong
register.

Use orex() to emit the REX prefix, consistent with all adjacent
branches in load().
---
 x86_64-gen.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/x86_64-gen.c b/x86_64-gen.c
index 2ca1ddec..af936b63 100644
--- a/x86_64-gen.c
+++ b/x86_64-gen.c
@@ -495,7 +495,8 @@ void load(int r, SValue *sv)
                     orex(0,r,0, 0xb8 + REG_VALUE(r)); /* mov $xx, r */
                     gen_le32(sv->c.i);
                 } else {
-                    o(0xc031 + REG_VALUE(r) * 0x900); /* xor r, r */
+                    orex(0, r, r, 0x31); /* xor r, r */
+                    o(0xc0 + REG_VALUE(r) * 9);
                 }
             } else {
                 orex(0,r,0, 0xb8 + REG_VALUE(r)); /* mov $xx, r */