From 8a9ab7c95e6ed898404db8fc5c9bca2a97196ab5 Mon Sep 17 00:00:00 2001
From: Cathal Mullan <contact@cathal.dev>
Date: Sat, 28 Feb 2026 19:33:23 +0000
Subject: [PATCH] Fix inline asm register allocator corrupting `rbx`

---
 src/inline_asm.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/inline_asm.rs b/src/inline_asm.rs
index ac0da06cbb..d6a3ae1df7 100644
--- a/src/inline_asm.rs
+++ b/src/inline_asm.rs
@@ -249,6 +249,12 @@ impl<'tcx> InlineAssemblyGenerator<'_, 'tcx> {
         let mut allocated = FxHashMap::<_, (bool, bool)>::default();
         let mut regs = vec![None; self.operands.len()];
 
+        // `rbx` is used by the asm wrapper.
+        // Mark `bx` as in-use so the allocator won't corrupt it.
+        if self.arch == InlineAsmArch::X86_64 {
+            allocated.insert(InlineAsmReg::X86(X86InlineAsmReg::bx), (true, true));
+        }
+
         // Add explicit registers to the allocated set.
         for (i, operand) in self.operands.iter().enumerate() {
             match *operand {