From cfd431808032919375dbedecd4cebc2b8cdbcc1a Mon Sep 17 00:00:00 2001
From: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Date: Wed, 9 Jul 2025 14:58:56 -0400
Subject: [PATCH] unittests: add 32-bit masking divide unit test

fails on main.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
---
 unittests/ASM/FEX_bugs/Divide32.asm | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
 create mode 100644 unittests/ASM/FEX_bugs/Divide32.asm

diff --git a/unittests/ASM/FEX_bugs/Divide32.asm b/unittests/ASM/FEX_bugs/Divide32.asm
new file mode 100644
index 000000000..1ead9e687
--- /dev/null
+++ b/unittests/ASM/FEX_bugs/Divide32.asm
@@ -0,0 +1,20 @@
+%ifdef CONFIG
+{
+  "RegData": {
+    "RAX": "0x80000001",
+    "RDX": "0x1"
+  }
+}
+%endif
+
+; FEX had a bug where we failed to ignore garbage upper bits of a 32-bit divisor
+; with div. This test does a division with garbage in the upper bits where the
+; result would differ if they were not ignored.
+
+; 0x100000003 / 0x2 = 0x80000001 remainder 1
+mov edx, 1
+mov eax, 3
+mov rcx, 0xdeadbeef00000002
+div ecx
+
+hlt