diff options
| author | Daniel Borkmann <daniel@iogearbox.net> | 2018-01-20 01:24:35 +0100 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2018-01-19 18:37:00 -0800 |
| commit | de0a444ddae61b77683c27cd390e518e33858d20 (patch) | |
| tree | b2bb3ce980577d8736bd0174aefa53b5655bf74e /arch | |
| parent | 2e4a30983b0f9b19b59e38bbf7427d7fdd480d98 (diff) | |
bpf, x86: small optimization in alu ops with imm
For the BPF_REG_0 (BPF_REG_A in cBPF, respectively), we can use
the short form of the opcode as dst mapping is on eax/rax and
thus save a byte per such operation. Added to add/sub/and/or/xor
for 32/64 bit when K immediate is used. There may be more such
low-hanging fruit to add in future as well.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/net/bpf_jit_comp.c | 35 |
1 files changed, 30 insertions, 5 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index b881a979efe1..5acee5139e28 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -152,6 +152,11 @@ static bool is_ereg(u32 reg) BIT(BPF_REG_AX)); } +static bool is_axreg(u32 reg) +{ + return reg == BPF_REG_0; +} + /* add modifiers if 'reg' maps to x64 registers r8..r15 */ static u8 add_1mod(u8 byte, u32 reg) { @@ -445,16 +450,36 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, else if (is_ereg(dst_reg)) EMIT1(add_1mod(0x40, dst_reg)); + /* b3 holds 'normal' opcode, b2 short form only valid + * in case dst is eax/rax. + */ switch (BPF_OP(insn->code)) { - case BPF_ADD: b3 = 0xC0; break; - case BPF_SUB: b3 = 0xE8; break; - case BPF_AND: b3 = 0xE0; break; - case BPF_OR: b3 = 0xC8; break; - case BPF_XOR: b3 = 0xF0; break; + case BPF_ADD: + b3 = 0xC0; + b2 = 0x05; + break; + case BPF_SUB: + b3 = 0xE8; + b2 = 0x2D; + break; + case BPF_AND: + b3 = 0xE0; + b2 = 0x25; + break; + case BPF_OR: + b3 = 0xC8; + b2 = 0x0D; + break; + case BPF_XOR: + b3 = 0xF0; + b2 = 0x35; + break; } if (is_imm8(imm32)) EMIT3(0x83, add_1reg(b3, dst_reg), imm32); + else if (is_axreg(dst_reg)) + EMIT1_off32(b2, imm32); else EMIT2_off32(0x81, add_1reg(b3, dst_reg), imm32); break; |