From: Daniel Borkmann Date: Sat, 24 Feb 2018 00:07:58 +0000 (+0100) Subject: bpf, x64: save one byte per shl/shr/sar when imm is 1 X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=88e69a1fcc1e67dec3025af64736a84532528242;p=linux.git bpf, x64: save one byte per shl/shr/sar when imm is 1 When we shift by one, we can use a different encoding where imm is not explicitly needed, which saves 1 byte per such op. Signed-off-by: Daniel Borkmann Signed-off-by: Alexei Starovoitov --- diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 4923d92f918d5..4bc36bd1b97a4 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -640,7 +640,11 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, case BPF_RSH: b3 = 0xE8; break; case BPF_ARSH: b3 = 0xF8; break; } - EMIT3(0xC1, add_1reg(b3, dst_reg), imm32); + + if (imm32 == 1) + EMIT2(0xD1, add_1reg(b3, dst_reg)); + else + EMIT3(0xC1, add_1reg(b3, dst_reg), imm32); break; case BPF_ALU | BPF_LSH | BPF_X: