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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 <davem@davemloft.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
David Miller 2018-11-26 13:42:41 -08:00 committed by Daniel Borkmann
parent 4afe60a97b
commit d8f3e978bd
1 changed files with 2 additions and 1 deletions
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3
net/core/filter.c
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@ -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) {