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Subject[PATCH v2 bpf-next 02/13] 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>
---
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 94b17bd30e00..a839c1a54276 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -702,6 +702,21 @@ static void emit_modrm_dstoff(u8 **pprog, u32 r1, u32 r2, int off)
*pprog = prog;
}

+/*
+ * Emit a REX byte if it will be necessary to address these registers
+ */
+static void maybe_emit_rex(u8 **pprog, u32 reg_rm, u32 reg_reg, bool wide)
+{
+ u8 *prog = *pprog;
+ int cnt = 0;
+
+ if (wide)
+ EMIT1(add_2mod(0x48, reg_rm, reg_reg));
+ else if (is_ereg(reg_rm) || is_ereg(reg_reg))
+ EMIT1(add_2mod(0x40, reg_rm, reg_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_rex(&prog, dst_reg, src_reg,
+ BPF_CLASS(insn->code) == BPF_ALU64);
EMIT2(b2, add_2reg(0xC0, dst_reg, src_reg));
break;

@@ -1301,20 +1314,16 @@ xadd: emit_modrm_dstoff(&prog, dst_reg, src_reg, 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_rex(&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_rex(&prog, dst_reg, src_reg,
+ BPF_CLASS(insn->code) == BPF_JMP);
EMIT2(0x85, add_2reg(0xC0, dst_reg, src_reg));
goto emit_cond_jmp;

@@ -1350,10 +1359,8 @@ xadd: emit_modrm_dstoff(&prog, dst_reg, src_reg, 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_rex(&prog, dst_reg, dst_reg,
+ BPF_CLASS(insn->code) == BPF_JMP);
EMIT2(0x85, add_2reg(0xC0, dst_reg, dst_reg));
goto emit_cond_jmp;
}
--
2.29.2.454.gaff20da3a2-goog
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