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KVM: x86 emulator: Avoid pushing back ModRM byte fetched for group decoding

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Although ModRM byte is fetched for group decoding, it is soon pushed
back to make decode_modrm() fetch it later again.

Now that ModRM flag can be found in the top level opcode tables, fetch
ModRM byte before group decoding to make the code simpler.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Takuya Yoshikawa 2012-04-30 17:48:25 +09:00 committed by Avi Kivity
parent 1c2545be05
commit 9f4260e73a
1 changed files with 3 additions and 5 deletions
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8
arch/x86/kvm/emulate.c
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@ -972,7 +972,6 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
ctxt->modrm_rm = base_reg = (ctxt->rex_prefix & 1) << 3; /* REG.B */ ctxt->modrm_rm = base_reg = (ctxt->rex_prefix & 1) << 3; /* REG.B */
} }
ctxt->modrm = insn_fetch(u8, ctxt);
ctxt->modrm_mod |= (ctxt->modrm & 0xc0) >> 6; ctxt->modrm_mod |= (ctxt->modrm & 0xc0) >> 6;
ctxt->modrm_reg |= (ctxt->modrm & 0x38) >> 3; ctxt->modrm_reg |= (ctxt->modrm & 0x38) >> 3;
ctxt->modrm_rm |= (ctxt->modrm & 0x07); ctxt->modrm_rm |= (ctxt->modrm & 0x07);
@ -3976,17 +3975,16 @@ done_prefixes:
} }
ctxt->d = opcode.flags; ctxt->d = opcode.flags;
if (ctxt->d & ModRM)
ctxt->modrm = insn_fetch(u8, ctxt);
while (ctxt->d & GroupMask) { while (ctxt->d & GroupMask) {
switch (ctxt->d & GroupMask) { switch (ctxt->d & GroupMask) {
case Group: case Group:
ctxt->modrm = insn_fetch(u8, ctxt);
--ctxt->_eip;
goffset = (ctxt->modrm >> 3) & 7; goffset = (ctxt->modrm >> 3) & 7;
opcode = opcode.u.group[goffset]; opcode = opcode.u.group[goffset];
break; break;
case GroupDual: case GroupDual:
ctxt->modrm = insn_fetch(u8, ctxt);
--ctxt->_eip;
goffset = (ctxt->modrm >> 3) & 7; goffset = (ctxt->modrm >> 3) & 7;
if ((ctxt->modrm >> 6) == 3) if ((ctxt->modrm >> 6) == 3)
opcode = opcode.u.gdual->mod3[goffset]; opcode = opcode.u.gdual->mod3[goffset];