For the BPF_REG_0 (BPF_REG_A in cBPF, respectively), we can use
the short form of the opcode as dst mapping is on eax/rax and
thus save a byte per such operation. Added to add/sub/and/or/xor
for 32/64 bit when K immediate is used. There may be more such
low-hanging fruit to add in future as well.
Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
Acked-by: Alexei Starovoitov <a...@kernel.org>
---
arch/x86/net/bpf_jit_comp.c | 35 ++++++++++++++++++++++++++++++-----
1 file changed, 30 insertions(+), 5 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index b881a97..5acee51 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -152,6 +152,11 @@ static bool is_ereg(u32 reg)
BIT(BPF_REG_AX));
}
+static bool is_axreg(u32 reg)
+{
+ return reg == BPF_REG_0;
+}
+
/* add modifiers if 'reg' maps to x64 registers r8..r15 */
static u8 add_1mod(u8 byte, u32 reg)
{
@@ -445,16 +450,36 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs,
u8 *image,
else if (is_ereg(dst_reg))
EMIT1(add_1mod(0x40, dst_reg));
+ /* b3 holds 'normal' opcode, b2 short form only valid
+ * in case dst is eax/rax.
+ */
switch (BPF_OP(insn->code)) {
- case BPF_ADD: b3 = 0xC0; break;
- case BPF_SUB: b3 = 0xE8; break;
- case BPF_AND: b3 = 0xE0; break;
- case BPF_OR: b3 = 0xC8; break;
- case BPF_XOR: b3 = 0xF0; break;
+ case BPF_ADD:
+ b3 = 0xC0;
+ b2 = 0x05;
+ break;
+ case BPF_SUB:
+ b3 = 0xE8;
+ b2 = 0x2D;
+ break;
+ case BPF_AND:
+ b3 = 0xE0;
+ b2 = 0x25;
+ break;
+ case BPF_OR:
+ b3 = 0xC8;
+ b2 = 0x0D;
+ break;
+ case BPF_XOR:
+ b3 = 0xF0;
+ b2 = 0x35;
+ break;
}
if (is_imm8(imm32))
EMIT3(0x83, add_1reg(b3, dst_reg), imm32);
+ else if (is_axreg(dst_reg))
+ EMIT1_off32(b2, imm32);
else
EMIT2_off32(0x81, add_1reg(b3, dst_reg), imm32);
break;
--
2.9.5
