From 95f62b6e8c058a965f1cfefb2520cad64f902ab3 Mon Sep 17 00:00:00 2001
From: Jonathan Campbell <jonathan@castus.tv>
Date: Fri, 20 Dec 2024 18:19:07 -0800
Subject: [PATCH] Dynamic x86 core: Reflect STI to normal core so 1-instruction
 delay is correctly emulated, which makes dynamic core, Windows XP, and
 SYSENTER/SYSEXIT possible

---
 CHANGELOG                      |  4 ++++
 src/cpu/core_dyn_x86.cpp       |  6 ++++++
 src/cpu/core_dyn_x86/decoder.h | 15 ++++++++-------
 3 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index 484e55c0a..65aed1a17 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,4 +1,8 @@
 Next
+  - Dynamic x86 core: Reflect STI instruction to normal core so that
+    the 1-instruction delay is correctly emulated. This makes it
+    possible to run Windows XP or Server 2003 with dynamic core and
+    SYSENTER/SYSEXIT emulation without random BSODs (joncampbell123).
   - Fix default code page. Instead of assuming 437 at all times, use
     437 for all IBM PC compatible modes and 932 for PC-98 emulation.
     (joncampbell123).
diff --git a/src/cpu/core_dyn_x86.cpp b/src/cpu/core_dyn_x86.cpp
index 2c63b5d93..66c119364 100644
--- a/src/cpu/core_dyn_x86.cpp
+++ b/src/cpu/core_dyn_x86.cpp
@@ -103,6 +103,7 @@ enum BlockReturnDynX86 {
 	BR_Cycles,
 	BR_Link1,BR_Link2,
 	BR_Opcode,
+	BR_Opcode2,
 	BR_Iret,
 	BR_CallBack,
 	BR_SMCBlock,
@@ -484,6 +485,11 @@ run_block:
 		CPU_Cycles=1;
 		if (!use_dynamic_core_with_paging) dosbox_allow_nonrecursive_page_fault = true;
 		return Safe_CPU_Core_Normal_Run();
+	case BR_Opcode2:
+		CPU_CycleLeft+=CPU_Cycles;
+		CPU_Cycles=2;
+		if (!use_dynamic_core_with_paging) dosbox_allow_nonrecursive_page_fault = true;
+		return Safe_CPU_Core_Normal_Run();
 	case BR_Link1:
 	case BR_Link2:
 		{
diff --git a/src/cpu/core_dyn_x86/decoder.h b/src/cpu/core_dyn_x86/decoder.h
index d6edaf909..438ac5011 100644
--- a/src/cpu/core_dyn_x86/decoder.h
+++ b/src/cpu/core_dyn_x86/decoder.h
@@ -3152,13 +3152,7 @@ restart_prefix:
 			gen_releasereg(DREG(TMPB));
 			break;
 		case 0xfb:		//STI
-			gen_releasereg(DREG(FLAGS));
-			gen_call_function((void *)&CPU_STI,"%Rd",DREG(TMPB));
-			dyn_check_bool_exception(DREG(TMPB));
-			gen_releasereg(DREG(TMPB));
-			dyn_check_irqrequest();
-			if (max_opcodes<=0) max_opcodes=1;		//Allow 1 extra opcode
-			break;
+			goto illegalopcode2; // signal "illegal" opcode so the core reflects to normal core which can then properly do the STI delay
 		case 0xfc:		//CLD
 			gen_protectflags();
 			gen_dop_word_imm(DOP_AND,true,DREG(FLAGS),~FLAG_DF);
@@ -3283,6 +3277,13 @@ illegalopcode:
 	gen_return(BR_Opcode);
 	dyn_closeblock();
 	goto finish_block;
+illegalopcode2:
+	dyn_set_eip_last();
+	dyn_reduce_cycles();
+	dyn_save_critical_regs();
+	gen_return(BR_Opcode2);
+	dyn_closeblock();
+	goto finish_block;
 finish_block:
 	/* Setup the correct end-address */
 	decode.active_block->page.end=(uint16_t)--decode.page.index;