From ca055cd7d5defb39e623fcf010a15ef5bb236f65 Mon Sep 17 00:00:00 2001
From: Simon Scherer <git69566@pinebound.com>
Date: Wed, 2 Sep 2026 16:39:52 +0200
Subject: [PATCH] unittests/ASM: Test FINCSTP for tag word

---
 unittests/ASM/FEX_bugs/fincstp_tag_word.asm | 24 +++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 unittests/ASM/FEX_bugs/fincstp_tag_word.asm

diff --git a/unittests/ASM/FEX_bugs/fincstp_tag_word.asm b/unittests/ASM/FEX_bugs/fincstp_tag_word.asm
new file mode 100644
index 000000000..ecdc5e86e
--- /dev/null
+++ b/unittests/ASM/FEX_bugs/fincstp_tag_word.asm
@@ -0,0 +1,24 @@
+%ifdef CONFIG
+{
+  "RegData": {
+    "RAX": "0xff"
+  }
+}
+%endif
+
+mov word [rel .fxsave_data + 0], 0x037f ; FCW
+mov byte [rel .fxsave_data + 4], 0xff   ; FTW
+
+; FSW = 0
+fxrstor [rel .fxsave_data]
+
+fincstp
+
+fxsave [rel .fxsave_data]
+movzx rax, byte [rel .fxsave_data + 4] ; FTW
+
+hlt
+
+align 4096
+.fxsave_data:
+times 64 dq 0