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 <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 4923d92..4bc36bd 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: