From 0ff2e6e1e3e56c688a41aafcba5f3c7f369c1ccd Mon Sep 17 00:00:00 2001
From: Ryan Houdek <Sonicadvance1@gmail.com>
Date: Mon, 23 Oct 2023 16:55:56 -0700
Subject: [PATCH] unittests: Adds test for bug from #3162

This PR has a bug around flags calculation and REP LODS{B,W,D,Q}.
This currently passes on main but fails on #3162.

Bug only occurs in 32-bit instead of 64-bit with the same test. Should
help diagnose the bugs in #3162.
---
 unittests/32Bit_ASM/FEX_bugs/rep_lods_bug.asm | 38 +++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 unittests/32Bit_ASM/FEX_bugs/rep_lods_bug.asm

diff --git a/unittests/32Bit_ASM/FEX_bugs/rep_lods_bug.asm b/unittests/32Bit_ASM/FEX_bugs/rep_lods_bug.asm
new file mode 100644
index 000000000..61a6166d8
--- /dev/null
+++ b/unittests/32Bit_ASM/FEX_bugs/rep_lods_bug.asm
@@ -0,0 +1,38 @@
+%ifdef CONFIG
+{
+  "RegData": {
+    "RAX": "0x52",
+    "RBX": "0x202",
+    "RCX": "0"
+  },
+  "Mode": "32BIT"
+}
+%endif
+
+; FEX had a bug that only manifests in 32-bit mode around pushing and popping flags around rep lobs{b,w,d,q}
+; This manifested as a corrupt CF and ZF flag even though rep lodsb isn't supposed to affect flags.
+; Test this by first storing zero to eflags, doing the operation and then loading it back.
+mov esi, 0xe000_0000
+mov esp, 0xe000_0800
+
+mov eax, 0x41424344
+mov [esi], eax
+
+mov eax, 0x51525354
+mov [esi + 4], eax
+
+mov eax, 0
+mov ecx, 7
+
+; Push zero and then load back in to eflags.
+push dword 0
+popfd
+
+; Do a rep lodsb, whichever size, doesn't matter.
+rep lodsb
+
+; Push flags and then load back in to ebx
+pushfd
+pop dword ebx
+
+hlt