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Subject[PATCH 03/40] KVM: x86 emulator: add support for group decoding
Date
Certain x86 instructions use bits 3:5 of the byte following the opcode as an
opcode extension, with the decode sometimes depending on bits 6:7 as well.
Add support for this in the main decoding table rather than an ad-hock
adaptation per opcode.

Signed-off-by: Avi Kivity <avi@qumranet.com>
---
arch/x86/kvm/x86_emulate.c | 33 +++++++++++++++++++++++++++------
1 files changed, 27 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
index 7958600..46ecf34 100644
--- a/arch/x86/kvm/x86_emulate.c
+++ b/arch/x86/kvm/x86_emulate.c
@@ -65,6 +65,9 @@
#define MemAbs (1<<9) /* Memory operand is absolute displacement */
#define String (1<<10) /* String instruction (rep capable) */
#define Stack (1<<11) /* Stack instruction (push/pop) */
+#define Group (1<<14) /* Bits 3:5 of modrm byte extend opcode */
+#define GroupDual (1<<15) /* Alternate decoding of mod == 3 */
+#define GroupMask 0xff /* Group number stored in bits 0:7 */

static u16 opcode_table[256] = {
/* 0x00 - 0x07 */
@@ -229,6 +232,12 @@ static u16 twobyte_table[256] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};

+static u16 group_table[] = {
+};
+
+static u16 group2_table[] = {
+};
+
/* EFLAGS bit definitions. */
#define EFLG_OF (1<<11)
#define EFLG_DF (1<<10)
@@ -763,7 +772,7 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
struct decode_cache *c = &ctxt->decode;
int rc = 0;
int mode = ctxt->mode;
- int def_op_bytes, def_ad_bytes;
+ int def_op_bytes, def_ad_bytes, group;

/* Shadow copy of register state. Committed on successful emulation. */

@@ -864,12 +873,24 @@ done_prefixes:
c->b = insn_fetch(u8, 1, c->eip);
c->d = twobyte_table[c->b];
}
+ }

- /* Unrecognised? */
- if (c->d == 0) {
- DPRINTF("Cannot emulate %02x\n", c->b);
- return -1;
- }
+ if (c->d & Group) {
+ group = c->d & GroupMask;
+ c->modrm = insn_fetch(u8, 1, c->eip);
+ --c->eip;
+
+ group = (group << 3) + ((c->modrm >> 3) & 7);
+ if ((c->d & GroupDual) && (c->modrm >> 6) == 3)
+ c->d = group2_table[group];
+ else
+ c->d = group_table[group];
+ }
+
+ /* Unrecognised? */
+ if (c->d == 0) {
+ DPRINTF("Cannot emulate %02x\n", c->b);
+ return -1;
}

if (mode == X86EMUL_MODE_PROT64 && (c->d & Stack))
--
1.5.4.5


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