KVM: x86 emulator: add support for group decoding

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>

1 files changed, 27 insertions, 6 deletions

diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
index 79586003397a..46ecf349a116 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))