* [PATCH] x86/emul: Calculate not_64bit during instruction decode
@ 2017-01-16 10:49 Andrew Cooper
2017-01-16 12:50 ` Jan Beulich
0 siblings, 1 reply; 2+ messages in thread
From: Andrew Cooper @ 2017-01-16 10:49 UTC (permalink / raw)
To: Xen-devel; +Cc: Andrew Cooper, Jan Beulich
... rather than repeating "generate_exception_if(mode_64bit(), EXC_UD);" in
the emulation switch statement.
Bloat-o-meter shows:
add/remove: 0/0 grow/shrink: 1/2 up/down: 8/-495 (-487)
function old new delta
per_cpu__state 98 106 +8
x86_decode 6782 6726 -56
x86_emulate 57160 56721 -439
The reason for x86_decode() getting smaller is that this change alters the
x86_decode_onebyte() switch statement from a chain of if()/else's to a jump
table. The jump table adds 250 bytes of data which bloat-o-meter clearly
can't see.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
I am also considering doing similar for vcpu cpuid checks, to split apart the
logic deciding on the feature to check from the emulation logic. This will
simplify some of the larger blocks, especially the mov emulation.
---
xen/arch/x86/x86_emulate/x86_emulate.c | 47 +++++++++++++++++++++-------------
1 file changed, 29 insertions(+), 18 deletions(-)
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index 445dcac..e9ac1fc 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1907,6 +1907,7 @@ struct x86_emulate_state {
uint8_t modrm, modrm_mod, modrm_reg, modrm_rm;
uint8_t rex_prefix;
bool lock_prefix;
+ bool not_64bit; /* Instruction not available in 64bit. */
opcode_desc_t desc;
union vex vex;
union evex evex;
@@ -1957,6 +1958,30 @@ x86_decode_onebyte(
switch ( ctxt->opcode )
{
+ case 0x06: /* push %%es */
+ case 0x07: /* pop %%es */
+ case 0x0e: /* push %%cs */
+ case 0x16: /* push %%ss */
+ case 0x17: /* pop %%ss */
+ case 0x1e: /* push %%ds */
+ case 0x1f: /* pop %%ds */
+ case 0x27: /* daa */
+ case 0x2f: /* das */
+ case 0x37: /* aaa */
+ case 0x3f: /* aas */
+ case 0x60: /* pusha */
+ case 0x61: /* popa */
+ case 0x62: /* bound */
+ case 0x82: /* Grp1 (x86/32 only) */
+ case 0xc4: /* les */
+ case 0xc5: /* lds */
+ case 0xce: /* into */
+ case 0xd4: /* aam */
+ case 0xd5: /* aad */
+ case 0xd6: /* salc */
+ state->not_64bit = true;
+ break;
+
case 0x90: /* nop / pause */
if ( repe_prefix() )
ctxt->opcode |= X86EMUL_OPC_F3(0, 0);
@@ -2624,6 +2649,8 @@ x86_emulate(
d = state.desc;
#define state (&state)
+ generate_exception_if(state->not_64bit && mode_64bit(), EXC_UD);
+
if ( ea.type == OP_REG )
ea.reg = decode_register(modrm_rm, &_regs,
(d & ByteOp) && !rex_prefix);
@@ -2832,8 +2859,6 @@ x86_emulate(
case 0x0e: /* push %%cs */
case 0x16: /* push %%ss */
case 0x1e: /* push %%ds */
- generate_exception_if(mode_64bit(), EXC_UD);
- /* fall through */
case X86EMUL_OPC(0x0f, 0xa0): /* push %%fs */
case X86EMUL_OPC(0x0f, 0xa8): /* push %%gs */
fail_if(ops->read_segment == NULL);
@@ -2846,8 +2871,6 @@ x86_emulate(
case 0x07: /* pop %%es */
case 0x17: /* pop %%ss */
case 0x1f: /* pop %%ds */
- generate_exception_if(mode_64bit(), EXC_UD);
- /* fall through */
case X86EMUL_OPC(0x0f, 0xa1): /* pop %%fs */
case X86EMUL_OPC(0x0f, 0xa9): /* pop %%gs */
fail_if(ops->write_segment == NULL);
@@ -2868,7 +2891,6 @@ x86_emulate(
uint8_t al = _regs.al;
unsigned int eflags = _regs._eflags;
- generate_exception_if(mode_64bit(), EXC_UD);
_regs._eflags &= ~(EFLG_CF|EFLG_AF|EFLG_SF|EFLG_ZF|EFLG_PF);
if ( ((al & 0x0f) > 9) || (eflags & EFLG_AF) )
{
@@ -2890,7 +2912,6 @@ x86_emulate(
case 0x37: /* aaa */
case 0x3f: /* aas */
- generate_exception_if(mode_64bit(), EXC_UD);
_regs._eflags &= ~EFLG_CF;
if ( (_regs.al > 9) || (_regs._eflags & EFLG_AF) )
{
@@ -2935,7 +2956,6 @@ x86_emulate(
_regs._eax, _regs._ecx, _regs._edx, _regs._ebx,
_regs._esp, _regs._ebp, _regs._esi, _regs._edi };
- generate_exception_if(mode_64bit(), EXC_UD);
fail_if(!ops->write);
for ( i = 0; i < 8; i++ )
if ( (rc = ops->write(x86_seg_ss, sp_pre_dec(op_bytes),
@@ -2950,7 +2970,6 @@ x86_emulate(
&_regs._edi, &_regs._esi, &_regs._ebp, &dummy_esp,
&_regs._ebx, &_regs._edx, &_regs._ecx, &_regs._eax };
- generate_exception_if(mode_64bit(), EXC_UD);
for ( i = 0; i < 8; i++ )
{
if ( (rc = read_ulong(x86_seg_ss, sp_post_inc(op_bytes),
@@ -2967,8 +2986,7 @@ x86_emulate(
case 0x62: /* bound */ {
unsigned long src_val2;
int lb, ub, idx;
- generate_exception_if(mode_64bit() || (src.type != OP_MEM),
- EXC_UD);
+ generate_exception_if(src.type != OP_MEM, EXC_UD);
if ( (rc = read_ulong(src.mem.seg, src.mem.off + op_bytes,
&src_val2, op_bytes, ctxt, ops)) )
goto done;
@@ -3127,10 +3145,7 @@ x86_emulate(
adjust_bnd(ctxt, ops, vex.pfx);
break;
- case 0x82: /* Grp1 (x86/32 only) */
- generate_exception_if(mode_64bit(), EXC_UD);
- /* Fallthrough. */
- case 0x80: case 0x81: case 0x83: /* Grp1 */
+ case 0x80: case 0x81: case 0x82: case 0x83: /* Grp1 */
switch ( modrm_reg & 7 )
{
case 0: goto add;
@@ -3518,7 +3533,6 @@ x86_emulate(
case 0xc4: /* les */
case 0xc5: /* lds */
- generate_exception_if(mode_64bit(), EXC_UD);
seg = (b & 1) * 3; /* es = 0, ds = 3 */
les:
generate_exception_if(src.type != OP_MEM, EXC_UD);
@@ -3606,7 +3620,6 @@ x86_emulate(
goto done;
case 0xce: /* into */
- generate_exception_if(mode_64bit(), EXC_UD);
if ( !(_regs._eflags & EFLG_OF) )
break;
src.val = EXC_OF;
@@ -3648,7 +3661,6 @@ x86_emulate(
case 0xd5: /* aad */ {
unsigned int base = (uint8_t)src.val;
- generate_exception_if(mode_64bit(), EXC_UD);
if ( b & 0x01 )
{
uint16_t ax = _regs.ax;
@@ -3670,7 +3682,6 @@ x86_emulate(
}
case 0xd6: /* salc */
- generate_exception_if(mode_64bit(), EXC_UD);
_regs.al = (_regs._eflags & EFLG_CF) ? 0xff : 0x00;
break;
--
2.1.4
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^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] x86/emul: Calculate not_64bit during instruction decode
2017-01-16 10:49 [PATCH] x86/emul: Calculate not_64bit during instruction decode Andrew Cooper
@ 2017-01-16 12:50 ` Jan Beulich
0 siblings, 0 replies; 2+ messages in thread
From: Jan Beulich @ 2017-01-16 12:50 UTC (permalink / raw)
To: Andrew Cooper; +Cc: Xen-devel
>>> On 16.01.17 at 11:49, <andrew.cooper3@citrix.com> wrote:
> ... rather than repeating "generate_exception_if(mode_64bit(), EXC_UD);" in
> the emulation switch statement.
>
> Bloat-o-meter shows:
>
> add/remove: 0/0 grow/shrink: 1/2 up/down: 8/-495 (-487)
> function old new delta
> per_cpu__state 98 106 +8
> x86_decode 6782 6726 -56
> x86_emulate 57160 56721 -439
>
> The reason for x86_decode() getting smaller is that this change alters the
> x86_decode_onebyte() switch statement from a chain of if()/else's to a jump
> table. The jump table adds 250 bytes of data which bloat-o-meter clearly
> can't see.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
> I am also considering doing similar for vcpu cpuid checks, to split apart the
> logic deciding on the feature to check from the emulation logic. This will
> simplify some of the larger blocks, especially the mov emulation.
Not sure about this one, specifically also in the context of the
SSEn/AVX support work I'm doing right now (where individual insn
variants have different CPUID dependencies).
Jan
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2017-01-16 12:50 ` Jan Beulich
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