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    Subject[PATCH bpf-next v7 02/11] bpf: x86: Factor out emission of REX byte
    From
    The JIT case for encoding atomic ops is about to get more
    complicated. In order to make the review & resulting code easier,
    let's factor out some shared helpers.

    Signed-off-by: Brendan Jackman <jackmanb@google.com>
    Acked-by: John Fastabend <john.fastabend@gmail.com>
    ---
    arch/x86/net/bpf_jit_comp.c | 39 ++++++++++++++++++++++---------------
    1 file changed, 23 insertions(+), 16 deletions(-)

    diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
    index 30526776fa78..f15c93275a18 100644
    --- a/arch/x86/net/bpf_jit_comp.c
    +++ b/arch/x86/net/bpf_jit_comp.c
    @@ -702,6 +702,21 @@ static void emit_insn_suffix(u8 **pprog, u32 ptr_reg, u32 val_reg, int off)
    *pprog = prog;
    }

    +/*
    + * Emit a REX byte if it will be necessary to address these registers
    + */
    +static void maybe_emit_mod(u8 **pprog, u32 dst_reg, u32 src_reg, bool is64)
    +{
    + u8 *prog = *pprog;
    + int cnt = 0;
    +
    + if (is64)
    + EMIT1(add_2mod(0x48, dst_reg, src_reg));
    + else if (is_ereg(dst_reg) || is_ereg(src_reg))
    + EMIT1(add_2mod(0x40, dst_reg, src_reg));
    + *pprog = prog;
    +}
    +
    /* LDX: dst_reg = *(u8*)(src_reg + off) */
    static void emit_ldx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
    {
    @@ -854,10 +869,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
    case BPF_OR: b2 = 0x09; break;
    case BPF_XOR: b2 = 0x31; break;
    }
    - if (BPF_CLASS(insn->code) == BPF_ALU64)
    - EMIT1(add_2mod(0x48, dst_reg, src_reg));
    - else if (is_ereg(dst_reg) || is_ereg(src_reg))
    - EMIT1(add_2mod(0x40, dst_reg, src_reg));
    + maybe_emit_mod(&prog, dst_reg, src_reg,
    + BPF_CLASS(insn->code) == BPF_ALU64);
    EMIT2(b2, add_2reg(0xC0, dst_reg, src_reg));
    break;

    @@ -1302,20 +1315,16 @@ st: if (is_imm8(insn->off))
    case BPF_JMP32 | BPF_JSGE | BPF_X:
    case BPF_JMP32 | BPF_JSLE | BPF_X:
    /* cmp dst_reg, src_reg */
    - if (BPF_CLASS(insn->code) == BPF_JMP)
    - EMIT1(add_2mod(0x48, dst_reg, src_reg));
    - else if (is_ereg(dst_reg) || is_ereg(src_reg))
    - EMIT1(add_2mod(0x40, dst_reg, src_reg));
    + maybe_emit_mod(&prog, dst_reg, src_reg,
    + BPF_CLASS(insn->code) == BPF_JMP);
    EMIT2(0x39, add_2reg(0xC0, dst_reg, src_reg));
    goto emit_cond_jmp;

    case BPF_JMP | BPF_JSET | BPF_X:
    case BPF_JMP32 | BPF_JSET | BPF_X:
    /* test dst_reg, src_reg */
    - if (BPF_CLASS(insn->code) == BPF_JMP)
    - EMIT1(add_2mod(0x48, dst_reg, src_reg));
    - else if (is_ereg(dst_reg) || is_ereg(src_reg))
    - EMIT1(add_2mod(0x40, dst_reg, src_reg));
    + maybe_emit_mod(&prog, dst_reg, src_reg,
    + BPF_CLASS(insn->code) == BPF_JMP);
    EMIT2(0x85, add_2reg(0xC0, dst_reg, src_reg));
    goto emit_cond_jmp;

    @@ -1351,10 +1360,8 @@ st: if (is_imm8(insn->off))
    case BPF_JMP32 | BPF_JSLE | BPF_K:
    /* test dst_reg, dst_reg to save one extra byte */
    if (imm32 == 0) {
    - if (BPF_CLASS(insn->code) == BPF_JMP)
    - EMIT1(add_2mod(0x48, dst_reg, dst_reg));
    - else if (is_ereg(dst_reg))
    - EMIT1(add_2mod(0x40, dst_reg, dst_reg));
    + maybe_emit_mod(&prog, dst_reg, dst_reg,
    + BPF_CLASS(insn->code) == BPF_JMP);
    EMIT2(0x85, add_2reg(0xC0, dst_reg, dst_reg));
    goto emit_cond_jmp;
    }
    --
    2.30.0.284.gd98b1dd5eaa7-goog
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