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authorDaniel Borkmann <daniel@iogearbox.net>2016-02-19 23:05:27 +0100
committerDavid S. Miller <davem@davemloft.net>2016-02-21 22:07:11 -0500
commit6205b9cf200d1c3dda5491666ddc33e7b70fe469 (patch)
tree78c48c223c2b45253361e929a1bffc291dd16925 /net/core
parent2f72959a9c1260ade234f353ccca91118151af66 (diff)
downloadlinux-6205b9cf200d1c3dda5491666ddc33e7b70fe469.tar.bz2
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>
Diffstat (limited to 'net/core')
-rw-r--r--net/core/filter.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/net/core/filter.c b/net/core/filter.c
index 8a0b8c3eb189..a3aba15a8025 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -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;