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bpf: x86: Factor out emission of REX byte

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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>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210114181751.768687-3-jackmanb@google.com
This commit is contained in:
Brendan Jackman 2021-01-14 18:17:42 +00:00 • committed by Alexei Starovoitov
parent 11c11d0751
commit 74007cfc1f
1 changed files with 23 additions and 16 deletions
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39
arch/x86/net/bpf_jit_comp.c
View file

@ -702,6 +702,21 @@ static void emit_insn_suffix(u8 **pprog, u32 ptr_reg, u32 val_reg, int off)
*pprog = prog; *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) */ /* LDX: dst_reg = *(u8*)(src_reg + off) */
static void emit_ldx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int 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_OR: b2 = 0x09; break;
case BPF_XOR: b2 = 0x31; break; case BPF_XOR: b2 = 0x31; break;
} }
if (BPF_CLASS(insn->code) == BPF_ALU64) maybe_emit_mod(&prog, dst_reg, src_reg,
EMIT1(add_2mod(0x48, dst_reg, src_reg)); BPF_CLASS(insn->code) == BPF_ALU64);
else if (is_ereg(dst_reg) || is_ereg(src_reg))
EMIT1(add_2mod(0x40, dst_reg, src_reg));
EMIT2(b2, add_2reg(0xC0, dst_reg, src_reg)); EMIT2(b2, add_2reg(0xC0, dst_reg, src_reg));
break; break;
@ -1302,20 +1315,16 @@ xadd:
case BPF_JMP32 | BPF_JSGE | BPF_X: case BPF_JMP32 | BPF_JSGE | BPF_X:
case BPF_JMP32 | BPF_JSLE | BPF_X: case BPF_JMP32 | BPF_JSLE | BPF_X:
/* cmp dst_reg, src_reg */ /* cmp dst_reg, src_reg */
if (BPF_CLASS(insn->code) == BPF_JMP) maybe_emit_mod(&prog, dst_reg, src_reg,
EMIT1(add_2mod(0x48, dst_reg, src_reg)); BPF_CLASS(insn->code) == BPF_JMP);
else if (is_ereg(dst_reg) || is_ereg(src_reg))
EMIT1(add_2mod(0x40, dst_reg, src_reg));
EMIT2(0x39, add_2reg(0xC0, dst_reg, src_reg)); EMIT2(0x39, add_2reg(0xC0, dst_reg, src_reg));
goto emit_cond_jmp; goto emit_cond_jmp;
case BPF_JMP | BPF_JSET | BPF_X: case BPF_JMP | BPF_JSET | BPF_X:
case BPF_JMP32 | BPF_JSET | BPF_X: case BPF_JMP32 | BPF_JSET | BPF_X:
/* test dst_reg, src_reg */ /* test dst_reg, src_reg */
if (BPF_CLASS(insn->code) == BPF_JMP) maybe_emit_mod(&prog, dst_reg, src_reg,
EMIT1(add_2mod(0x48, dst_reg, src_reg)); BPF_CLASS(insn->code) == BPF_JMP);
else if (is_ereg(dst_reg) || is_ereg(src_reg))
EMIT1(add_2mod(0x40, dst_reg, src_reg));
EMIT2(0x85, add_2reg(0xC0, dst_reg, src_reg)); EMIT2(0x85, add_2reg(0xC0, dst_reg, src_reg));
goto emit_cond_jmp; goto emit_cond_jmp;
@ -1351,10 +1360,8 @@ xadd:
case BPF_JMP32 | BPF_JSLE | BPF_K: case BPF_JMP32 | BPF_JSLE | BPF_K:
/* test dst_reg, dst_reg to save one extra byte */ /* test dst_reg, dst_reg to save one extra byte */
if (imm32 == 0) { if (imm32 == 0) {
if (BPF_CLASS(insn->code) == BPF_JMP) maybe_emit_mod(&prog, dst_reg, dst_reg,
EMIT1(add_2mod(0x48, dst_reg, dst_reg)); BPF_CLASS(insn->code) == BPF_JMP);
else if (is_ereg(dst_reg))
EMIT1(add_2mod(0x40, dst_reg, dst_reg));
EMIT2(0x85, add_2reg(0xC0, dst_reg, dst_reg)); EMIT2(0x85, add_2reg(0xC0, dst_reg, dst_reg));
goto emit_cond_jmp; goto emit_cond_jmp;
} }