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| author | Daniel Borkmann <daniel@iogearbox.net> | 2018-02-24 03:07:58 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2018-02-24 09:50:00 +0300 |
| commit | 88e69a1fcc1e67dec3025af64736a84532528242 (patch) | |
| tree | 3b7969431a064be0e3079257d01f895bf5692f97 | |
| parent | ee07862f7b4594d390b978f6636a6a6191632ab3 (diff) | |
| download | linux-88e69a1fcc1e67dec3025af64736a84532528242.tar.xz | |
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>
| -rw-r--r-- | arch/x86/net/bpf_jit_comp.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 4923d92f918d..4bc36bd1b97a 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: |