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Commit 6205b9cf authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller
Browse files

bpf: don't emit mov A,A on return 



While debugging with bpf_jit_disasm I noticed emissions of 'mov %eax,%eax',
and found that this comes from BPF_RET | BPF_A translations from classic
BPF. Emitting this is unnecessary as BPF_REG_A is mapped into BPF_REG_0
already, therefore only emit a mov when immediates are used as return value.

Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2f72959a

net/core/filter.c

+6 −4
Original line number Diff line number Diff line
@@ -530,12 +530,14 @@ static int bpf_convert_filter(struct sock_filter *prog, int len, 
			*insn = BPF_MOV64_REG(BPF_REG_A, BPF_REG_TMP);

			break;



		/* RET_K, RET_A are remaped into 2 insns. */

		/* RET_K is remaped into 2 insns. RET_A case doesn't need an

		 * extra mov as BPF_REG_0 is already mapped into BPF_REG_A.

		 */

		case BPF_RET | BPF_A:

		case BPF_RET | BPF_K:

			*insn++ = BPF_MOV32_RAW(BPF_RVAL(fp->code) == BPF_K ?

						BPF_K : BPF_X, BPF_REG_0,

						BPF_REG_A, fp->k);

			if (BPF_RVAL(fp->code) == BPF_K)

				*insn++ = BPF_MOV32_RAW(BPF_K, BPF_REG_0,

							0, fp->k);

			*insn = BPF_EXIT_INSN();

			break;