Re: [Patch] (big) real mode emulation - jmp rel

Nitin A Kamble
2007-08-17T22:24:59Z

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On Fri, 2007-08-17 at 05:24 -0700, Avi Kivity wrote:
> A file scope function would indeed be uglier. But the macro has more
> serious problems; it's impossible to understand how variables are
> affected since nobody expects function local variables whose address
> is
> not taken to change after something that looks like a macro is called.
>
> At the very least, it needs to be in uppercase so that people know
> something funny is going on. But it's really better as a function.
>
> (and yes, the rest of the file uses macros. and yes, the rest of the
> file is an unmaintainable mess)

Hi Avi,
I tried either ways, and to me the macro looks cleaner. Now I have
upper-cased it for your satisfaction. :)
Also attached the "jmp rel short" emulation patch.

--
Thanks & Regards,
Nitin
Open Source Technology Center, Intel Corporation
-----------------------------------------------------------------
The mind is like a parachute; it works much better when it's open

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commit 47259a989606e37e5ba24f6722a8258368e6d0a2
Author: Nitin A Kamble <nitin.a.kamble@intel.com>
Date: Fri Aug 17 18:39:29 2007 -0700

Implementing emulation of instruction
jmp rel short imm8
opcode: 0xeb
Signed-off-by: Nitin A Kamble <nitin.a.kamble@intel.com>

diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index 393dfb6..fed0b2a 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -148,7 +148,7 @@ static u8 opcode_table[256] = {
/* 0xE0 - 0xE7 */
0, 0, 0, 0, 0, 0, 0, 0,
/* 0xE8 - 0xEF */
- 0, SrcImm|ImplicitOps, 0, 0, 0, 0, 0, 0,
+ 0, SrcImm|ImplicitOps, 0, SrcImmByte|ImplicitOps, 0, 0, 0, 0,
/* 0xF0 - 0xF7 */
0, 0, 0, 0,
ImplicitOps, 0,
@@ -1029,6 +1029,7 @@ grp2: /* Grp2 */
src.val = _regs[VCPU_REGS_RCX];
goto grp2;
case 0xe9: /* jmp rel */
+ case 0xeb: /* jmp rel short */
JMP_REL(src.val);
no_wb = 1; /* Disable writeback. */
break;

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commit 17994104bef0da3d182d2b8736fbd1cf8d4a77f0
Author: Nitin A Kamble <nitin.a.kamble@intel.com>
Date: Fri Aug 17 18:33:07 2007 -0700

Implement emulation of instruction "jmp rel" opcode 0xe9

Signed-off-by: Nitin A Kamble <nitin.a.kamble@intel.com>

diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index b196d25..393dfb6 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -145,8 +145,10 @@ static u8 opcode_table[256] = {
0, 0, 0, 0,
/* 0xD8 - 0xDF */
0, 0, 0, 0, 0, 0, 0, 0,
- /* 0xE0 - 0xEF */
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ /* 0xE0 - 0xE7 */
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ /* 0xE8 - 0xEF */
+ 0, SrcImm|ImplicitOps, 0, 0, 0, 0, 0, 0,
/* 0xF0 - 0xF7 */
0, 0, 0, 0,
ImplicitOps, 0,
@@ -447,6 +449,12 @@ struct operand {
(((reg) + _inc) & ((1UL << (ad_bytes << 3)) - 1)); \
} while (0)

+#define JMP_REL(rel) \
+ do { \
+ _eip += (int)(rel); \
+ _eip = ((op_bytes == 2) ? (uint16_t)_eip : (uint32_t)_eip); \
+ } while (0)
+
/*
* Given the 'reg' portion of a ModRM byte, and a register block, return a
* pointer into the block that addresses the relevant register.
@@ -1020,6 +1028,10 @@ grp2: /* Grp2 */
case 0xd2 ... 0xd3: /* Grp2 */
src.val = _regs[VCPU_REGS_RCX];
goto grp2;
+ case 0xe9: /* jmp rel */
+ JMP_REL(src.val);
+ no_wb = 1; /* Disable writeback. */
+ break;
case 0xf6 ... 0xf7: /* Grp3 */
switch (modrm_reg) {
case 0 ... 1: /* test */