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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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