diff options
| author | Daniel Borkmann <daniel@iogearbox.net> | 2018-02-24 01:08:00 +0100 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2018-02-24 07:50:00 +0100 |
| commit | d806a0cf2a1ddb97c91d902ef1c8219e1e2b2c4c (patch) | |
| tree | 3d168b1decd203600c39c67ba730eabb7178e829 | |
| parent | bpf, x64: save several bytes by using mov over movabsq when possible (diff) | |
| download | linux-d806a0cf2a1ddb97c91d902ef1c8219e1e2b2c4c.tar.xz linux-d806a0cf2a1ddb97c91d902ef1c8219e1e2b2c4c.zip | |
bpf, x64: save several bytes when mul dest is r0/r3 anyway
Instead of unconditionally performing push/pop on rax/rdx
in case of multiplication, we can save a few bytes in case
of dest register being either BPF r0 (rax) or r3 (rdx)
since the result is written in there anyway.
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 | 21 |
1 files changed, 11 insertions, 10 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index f3e5cd8c1e68..9895ca383023 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -615,8 +615,10 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, case BPF_ALU | BPF_MUL | BPF_X: case BPF_ALU64 | BPF_MUL | BPF_K: case BPF_ALU64 | BPF_MUL | BPF_X: - EMIT1(0x50); /* push rax */ - EMIT1(0x52); /* push rdx */ + if (dst_reg != BPF_REG_0) + EMIT1(0x50); /* push rax */ + if (dst_reg != BPF_REG_3) + EMIT1(0x52); /* push rdx */ /* mov r11, dst_reg */ EMIT_mov(AUX_REG, dst_reg); @@ -636,14 +638,13 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, /* mul(q) r11 */ EMIT2(0xF7, add_1reg(0xE0, AUX_REG)); - /* mov r11, rax */ - EMIT_mov(AUX_REG, BPF_REG_0); - - EMIT1(0x5A); /* pop rdx */ - EMIT1(0x58); /* pop rax */ - - /* mov dst_reg, r11 */ - EMIT_mov(dst_reg, AUX_REG); + if (dst_reg != BPF_REG_3) + EMIT1(0x5A); /* pop rdx */ + if (dst_reg != BPF_REG_0) { + /* mov dst_reg, rax */ + EMIT_mov(dst_reg, BPF_REG_0); + EMIT1(0x58); /* pop rax */ + } break; /* shifts */ |