From d3f507c2a2cc190d417a257b40a49a4a2926e3d3 Mon Sep 17 00:00:00 2001
From: Aaron Plattner <aplattner@nvidia.com>
Date: Tue, 6 Feb 2007 14:57:22 -0800
Subject: [PATCH] Add an RDTSC implementation to the x86 emulator.

This instruction is being used in some debug VBIOSes.  This implementation
doesn't even try to be accurate.  Instead, it just increments the counter by a
fixed amount every time an rdtsc instruction in encountered, to avoid divides by
zero.
---
 hw/xfree86/x86emu/ops2.c | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/hw/xfree86/x86emu/ops2.c b/hw/xfree86/x86emu/ops2.c
index 7b0156aaa..8c6c53539 100644
--- a/hw/xfree86/x86emu/ops2.c
+++ b/hw/xfree86/x86emu/ops2.c
@@ -63,6 +63,40 @@ static void x86emuOp2_illegal_op(
 
 #define xorl(a,b)   ((a) && !(b)) || (!(a) && (b))
 
+/****************************************************************************
+REMARKS:
+Handles opcode 0x0f,0x31
+****************************************************************************/
+static void x86emuOp2_rdtsc(u8 X86EMU_UNUSED(op2))
+{
+#ifdef __HAS_LONG_LONG__
+    static u64 counter = 0;
+#else
+    static u32 counter = 0;
+#endif
+
+    counter += 0x10000;
+
+    /* read timestamp counter */
+    /*
+     * Note that instead of actually trying to accurately measure this, we just
+     * increase the counter by a fixed amount every time we hit one of these
+     * instructions.  Feel free to come up with a better method.
+     */
+    START_OF_INSTR();
+    DECODE_PRINTF("RDTSC\n");
+    TRACE_AND_STEP();
+#ifdef __HAS_LONG_LONG__
+    M.x86.R_EAX = counter & 0xffffffff;
+    M.x86.R_EDX = counter >> 32;
+#else
+    M.x86.R_EAX = counter;
+    M.x86.R_EDX = 0;
+#endif
+    DECODE_CLEAR_SEGOVR();
+    END_OF_INSTR();
+}
+
 /****************************************************************************
 REMARKS:
 Handles opcode 0x0f,0x80-0x8F
@@ -2580,7 +2614,7 @@ void (*x86emu_optab2[256])(u8) =
 /*  0x2f */ x86emuOp2_illegal_op,
 
 /*  0x30 */ x86emuOp2_illegal_op,
-/*  0x31 */ x86emuOp2_illegal_op,
+/*  0x31 */ x86emuOp2_rdtsc,
 /*  0x32 */ x86emuOp2_illegal_op,
 /*  0x33 */ x86emuOp2_illegal_op,
 /*  0x34 */ x86emuOp2_illegal_op,