From 2abf91603ec80e4c28c3f7e0b3336f483feb097f Mon Sep 17 00:00:00 2001
From: "Herman S." <429230+has207@users.noreply.github.com>
Date: Wed, 15 Oct 2025 11:57:49 +0900
Subject: [PATCH] [x64/Linux] Ensure EmitHostToGuestThunk saves rsi

---
 src/xenia/cpu/backend/x64/x64_backend.cc | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/xenia/cpu/backend/x64/x64_backend.cc b/src/xenia/cpu/backend/x64/x64_backend.cc
index e979df258..4b7d0e089 100644
--- a/src/xenia/cpu/backend/x64/x64_backend.cc
+++ b/src/xenia/cpu/backend/x64/x64_backend.cc
@@ -693,10 +693,14 @@ HostToGuestThunk X64HelperEmitter::EmitHostToGuestThunk() {
   EmitSaveNonvolatileRegs();
 
   mov(rax, rdi);
-  // mov(rsi, rsi);   // context
+  // Save context register (RSI is volatile on Linux/Mac System V ABI, but we
+  // need it preserved)
+  mov(qword[rsp + offsetof(StackLayout::Thunk, xmm[0])], rsi);
   mov(rdi, ptr[rsi + offsetof(ppc::PPCContext, virtual_membase)]);  // membase
   mov(rcx, rdx);  // return address
   call(rax);
+  // Restore context register
+  mov(rsi, qword[rsp + offsetof(StackLayout::Thunk, xmm[0])]);
 
   EmitLoadNonvolatileRegs();