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Commit d806a0cf authored by Daniel Borkmann's avatar Daniel Borkmann Committed by Alexei Starovoitov
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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: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 6fe8b9c1

arch/x86/net/bpf_jit_comp.c

+11 −10
Original line number Diff line number Diff line
@@ -615,7 +615,9 @@ 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:

			if (dst_reg != BPF_REG_0)

				EMIT1(0x50); /* push rax */

			if (dst_reg != BPF_REG_3)

				EMIT1(0x52); /* push rdx */



			/* mov r11, 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);



			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 */



			/* mov dst_reg, r11 */

			EMIT_mov(dst_reg, AUX_REG);

			}

			break;



			/* shifts */