Commit 88e69a1f authored Feb 24, 2018 by Daniel Borkmann Committed by Alexei Starovoitov Feb 23, 2018

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>

parent ee07862f

arch/x86/net/bpf_jit_comp.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -640,6 +640,10 @@ 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;
		}

		if (imm32 == 1)
		EMIT2(0xD1, add_1reg(b3, dst_reg));
		else
		EMIT3(0xC1, add_1reg(b3, dst_reg), imm32);
		break;