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    Subject[PATCH] x86: x86-opcode-map.txt: explain CALLW discrepancy between Intel and AMD
    Date
    In 64-bit mode, AMD and Intel CPUs treat 0x66 prefix before branch
    insns differently. For near branches, it affects decode too since
    immediate offset's width is different.

    Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
    CC: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    CC: Ingo Molnar <mingo@kernel.org>
    CC: Oleg Nesterov <oleg@redhat.com>
    CC: linux-kernel@vger.kernel.org
    ---
    arch/x86/lib/x86-opcode-map.txt | 9 +++++++++
    1 file changed, 9 insertions(+)

    diff --git a/arch/x86/lib/x86-opcode-map.txt b/arch/x86/lib/x86-opcode-map.txt
    index 1a2be7c..816488c 100644
    --- a/arch/x86/lib/x86-opcode-map.txt
    +++ b/arch/x86/lib/x86-opcode-map.txt
    @@ -273,6 +273,9 @@ dd: ESC
    de: ESC
    df: ESC
    # 0xe0 - 0xef
    +# Note: "forced64" is Intel CPU behavior: they ignore 0x66 prefix
    +# in 64-bit mode. AMD CPUs accept 0x66 prefix, it causes RIP truncation
    +# to 16 bits. In 32-bit mode, 0x66 is accepted by both Intel and AMD.
    e0: LOOPNE/LOOPNZ Jb (f64)
    e1: LOOPE/LOOPZ Jb (f64)
    e2: LOOP Jb (f64)
    @@ -281,6 +284,10 @@ e4: IN AL,Ib
    e5: IN eAX,Ib
    e6: OUT Ib,AL
    e7: OUT Ib,eAX
    +# With 0x66 prefix in 64-bit mode, for AMD CPUs immediate offset
    +# in "near" jumps and calls is 16-bit. For CALL,
    +# push of return address is 16-bit wide, RSP is decremented by 2
    +# but is not truncated to 16 bits, unlike RIP.
    e8: CALL Jz (f64)
    e9: JMP-near Jz (f64)
    ea: JMP-far Ap (i64)
    @@ -456,6 +463,7 @@ AVXcode: 1
    7e: movd/q Ey,Pd | vmovd/q Ey,Vy (66),(v1) | vmovq Vq,Wq (F3),(v1)
    7f: movq Qq,Pq | vmovdqa Wx,Vx (66) | vmovdqu Wx,Vx (F3)
    # 0x0f 0x80-0x8f
    +# Note: "forced64" is Intel CPU behavior (see comment about CALL insn).
    80: JO Jz (f64)
    81: JNO Jz (f64)
    82: JB/JC/JNAE Jz (f64)
    @@ -842,6 +850,7 @@ EndTable
    GrpTable: Grp5
    0: INC Ev
    1: DEC Ev
    +# Note: "forced64" is Intel CPU behavior (see comment about CALL insn).
    2: CALLN Ev (f64)
    3: CALLF Ep
    4: JMPN Ev (f64)
    --
    1.8.1.4


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