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KVM: x86 emulator: Any legacy prefix after a REX prefix nullifies its effect

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This patch modifies the management of REX prefix according behavior
I saw in Xen 3.1.  In Xen, this modification has been introduced by
Jan Beulich.

http://lists.xensource.com/archives/html/xen-changelog/2007-01/msg00081.html

Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Laurent Vivier 2007-09-25 13:36:40 +02:00 committed by Avi Kivity
parent a22436b7b8
commit b4c6abfef4
1 changed files with 15 additions and 9 deletions
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24
drivers/kvm/x86_emulate.c
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@ -521,7 +521,6 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
{
struct decode_cache *c = &ctxt->decode;
u8 sib, rex_prefix = 0;
unsigned int i;
int rc = 0;
int mode = ctxt->mode;
int index_reg = 0, base_reg = 0, scale, rip_relative = 0;
@ -551,7 +550,7 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
}
/* Legacy prefixes. */
for (i = 0; i < 8; i++) {
for (;;) {
switch (c->b = insn_fetch(u8, 1, c->eip)) {
case 0x66: /* operand-size override */
c->op_bytes ^= 6; /* switch between 2/4 bytes */
@ -582,6 +581,11 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
case 0x36: /* SS override */
c->override_base = &ctxt->ss_base;
break;
case 0x40 ... 0x4f: /* REX */
if (mode != X86EMUL_MODE_PROT64)
goto done_prefixes;
rex_prefix = c->b;
continue;
case 0xf0: /* LOCK */
c->lock_prefix = 1;
break;
@ -592,19 +596,21 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
default:
goto done_prefixes;
}
/* Any legacy prefix after a REX prefix nullifies its effect. */
rex_prefix = 0;
}
done_prefixes:
/* REX prefix. */
if ((mode == X86EMUL_MODE_PROT64) && ((c->b & 0xf0) == 0x40)) {
rex_prefix = c->b;
if (c->b & 8)
if (rex_prefix) {
if (rex_prefix & 8)
c->op_bytes = 8; /* REX.W */
c->modrm_reg = (c->b & 4) << 1; /* REX.R */
index_reg = (c->b & 2) << 2; /* REX.X */
c->modrm_rm = base_reg = (c->b & 1) << 3; /* REG.B */
c->b = insn_fetch(u8, 1, c->eip);
c->modrm_reg = (rex_prefix & 4) << 1; /* REX.R */
index_reg = (rex_prefix & 2) << 2; /* REX.X */
c->modrm_rm = base_reg = (rex_prefix & 1) << 3; /* REG.B */
}
/* Opcode byte(s). */