Commit 6205b9cf authored Feb 19, 2016 by Daniel Borkmann Committed by David S. Miller Feb 21, 2016

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: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David 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 @@ do_pass:
		*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;

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