Module Name: src
Committed By: alnsn
Date: Fri May 23 22:04:09 UTC 2014
Modified Files:
src/sys/net: bpfjit.c
Log Message:
Enable ABC optimization when one branch returns 0.
To generate a diff of this commit:
cvs rdiff -u -r1.10 -r1.11 src/sys/net/bpfjit.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/net/bpfjit.c
diff -u src/sys/net/bpfjit.c:1.10 src/sys/net/bpfjit.c:1.11
--- src/sys/net/bpfjit.c:1.10 Fri May 23 19:51:16 2014
+++ src/sys/net/bpfjit.c Fri May 23 22:04:09 2014
@@ -1,4 +1,4 @@
-/* $NetBSD: bpfjit.c,v 1.10 2014/05/23 19:51:16 alnsn Exp $ */
+/* $NetBSD: bpfjit.c,v 1.11 2014/05/23 22:04:09 alnsn Exp $ */
/*-
* Copyright (c) 2011-2014 Alexander Nasonov.
@@ -31,9 +31,9 @@
#include <sys/cdefs.h>
#ifdef _KERNEL
-__KERNEL_RCSID(0, "$NetBSD: bpfjit.c,v 1.10 2014/05/23 19:51:16 alnsn Exp $");
+__KERNEL_RCSID(0, "$NetBSD: bpfjit.c,v 1.11 2014/05/23 22:04:09 alnsn Exp $");
#else
-__RCSID("$NetBSD: bpfjit.c,v 1.10 2014/05/23 19:51:16 alnsn Exp $");
+__RCSID("$NetBSD: bpfjit.c,v 1.11 2014/05/23 22:04:09 alnsn Exp $");
#endif
#include <sys/types.h>
@@ -1146,7 +1146,27 @@ optimize_pass2(const struct bpf_insn *in
switch (BPF_CLASS(pc->code)) {
case BPF_RET:
- abc_length = 0;
+ /*
+ * It's quite common for bpf programs to
+ * check packet bytes in increasing order
+ * and return zero if bytes don't match
+ * specified critetion. Such programs disable
+ * ABC optimization completely because for
+ * every jump there is a branch with no read
+ * instruction.
+ * With no side effects, BPF_RET+BPF_K 0 is
+ * indistinguishable from out-of-bound load.
+ * Therefore, abc_length can be set to
+ * MAX_ABC_LENGTH and enable ABC for many
+ * bpf programs.
+ * If this optimization pass encounters any
+ * instruction with a side effect, it will
+ * reset abc_length.
+ */
+ if (BPF_RVAL(pc->code) == BPF_K && pc->k == 0)
+ abc_length = MAX_ABC_LENGTH;
+ else
+ abc_length = 0;
break;
case BPF_JMP:
