From d8f3e978bd30014081c599456285ca1d58c2aae1 Mon Sep 17 00:00:00 2001 From: David Miller Date: Mon, 26 Nov 2018 13:42:41 -0800 Subject: [PATCH] bpf: Avoid unnecessary instruction in convert_bpf_ld_abs() 'offset' is constant and if it is zero, no need to subtract it from BPF_REG_TMP. Signed-off-by: David S. Miller Signed-off-by: Daniel Borkmann --- net/core/filter.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/core/filter.c b/net/core/filter.c index aa274679965d..f50ea971f7a9 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -463,7 +463,8 @@ static bool convert_bpf_ld_abs(struct sock_filter *fp, struct bpf_insn **insnp) bool ldx_off_ok = offset <= S16_MAX; *insn++ = BPF_MOV64_REG(BPF_REG_TMP, BPF_REG_H); - *insn++ = BPF_ALU64_IMM(BPF_SUB, BPF_REG_TMP, offset); + if (offset) + *insn++ = BPF_ALU64_IMM(BPF_SUB, BPF_REG_TMP, offset); *insn++ = BPF_JMP_IMM(BPF_JSLT, BPF_REG_TMP, size, 2 + endian + (!ldx_off_ok * 2)); if (ldx_off_ok) {