[src/trunk]: src/sys/net Implement unconditional jump to "return 0" for loads...

[alnsn <alnsn%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/e4b1642780cc
branches:  trunk
changeset: 329424:e4b1642780cc
user:      alnsn <alnsn%NetBSD.org@localhost>
date:      Fri May 23 19:11:22 2014 +0000

description:
Implement unconditional jump to "return 0" for loads at UINT32_MAX+1 or greater.

diffstat:

 sys/net/bpfjit.c |  73 ++++++++++++++++++++++++++++++++++++-------------------
 1 files changed, 48 insertions(+), 25 deletions(-)

diffs (147 lines):

diff -r ad6e7f0f4ad1 -r e4b1642780cc sys/net/bpfjit.c
--- a/sys/net/bpfjit.c  Fri May 23 19:05:35 2014 +0000
+++ b/sys/net/bpfjit.c  Fri May 23 19:11:22 2014 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: bpfjit.c,v 1.8 2014/05/22 13:35:45 alnsn Exp $ */
+/*     $NetBSD: bpfjit.c,v 1.9 2014/05/23 19:11:22 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 1.8 2014/05/22 13:35:45 alnsn Exp $");
+__KERNEL_RCSID(0, "$NetBSD: bpfjit.c,v 1.9 2014/05/23 19:11:22 alnsn Exp $");
 #else
-__RCSID("$NetBSD: bpfjit.c,v 1.8 2014/05/22 13:35:45 alnsn Exp $");
+__RCSID("$NetBSD: bpfjit.c,v 1.9 2014/05/23 19:11:22 alnsn Exp $");
 #endif
 
 #include <sys/types.h>
@@ -94,8 +94,11 @@
 #define BJ_INIT_ABIT    BJ_INIT_MBIT(BPF_MEMWORDS)
 #define BJ_INIT_XBIT    BJ_INIT_MBIT(BPF_MEMWORDS + 1)
 
-typedef uint32_t bpfjit_abc_length_t;
-#define MAX_ABC_LENGTH UINT32_MAX
+/*
+ * Datatype for Array Bounds Check Elimination (ABC) pass.
+ */
+typedef uint64_t bpfjit_abc_length_t;
+#define MAX_ABC_LENGTH (UINT32_MAX + UINT64_C(4)) /* max. width is 4 */
 
 struct bpfjit_stack
 {
@@ -152,8 +155,7 @@
        /*
         * If positive, emit "if (buflen < check_length) return 0"
         * out-of-bounds check.
-        * We assume that buflen is never equal to UINT32_MAX (otherwise,
-        * we'd need a special bool variable to emit unconditional "return 0").
+        * Values greater than UINT32_MAX generate unconditional "return 0".
         */
        bpfjit_abc_length_t check_length;
 };
@@ -903,8 +905,11 @@
        }
 
        if (rv && length != NULL) {
-               *length = (pc->k > UINT32_MAX - width) ?
-                   UINT32_MAX : pc->k + width;
+               /*
+                * Values greater than UINT32_MAX will generate
+                * unconditional "return 0".
+                */
+               *length = (uint32_t)pc->k + width;
        }
 
        return rv;
@@ -1324,6 +1329,7 @@
        struct bpfjit_jump *bjump, *jtf;
 
        struct sljit_jump *to_mchain_jump;
+       bool unconditional_ret;
 
        uint32_t jt, jf;
 
@@ -1405,8 +1411,6 @@
                if (insn_dat[i].unreachable)
                        continue;
 
-               to_mchain_jump = NULL;
-
                /*
                 * Resolve jumps to the current insn.
                 */
@@ -1421,23 +1425,36 @@
                        }
                }
 
-               if (read_pkt_insn(&insns[i], NULL) &&
-                   insn_dat[i].u.rdata.check_length > 0) {
-                       /* if (buflen < check_length) return 0; */
-                       jump = sljit_emit_cmp(compiler,
-                           SLJIT_C_LESS,
-                           BJ_BUFLEN, 0,
-                           SLJIT_IMM,
-                           insn_dat[i].u.rdata.check_length);
-                       if (jump == NULL)
-                               goto fail;
+               to_mchain_jump = NULL;
+               unconditional_ret = false;
+
+               if (read_pkt_insn(&insns[i], NULL)) {
+                       if (insn_dat[i].u.rdata.check_length > UINT32_MAX) {
+                               /* Jump to "return 0" unconditionally. */
+                               unconditional_ret = true;
+                               jump = sljit_emit_jump(compiler, SLJIT_JUMP);
+                               if (jump == NULL)
+                                       goto fail;
+                               if (!append_jump(jump, &ret0,
+                                   &ret0_size, &ret0_maxsize))
+                                       goto fail;
+                       } else if (insn_dat[i].u.rdata.check_length > 0) {
+                               /* if (buflen < check_length) return 0; */
+                               jump = sljit_emit_cmp(compiler,
+                                   SLJIT_C_LESS,
+                                   BJ_BUFLEN, 0,
+                                   SLJIT_IMM,
+                                   insn_dat[i].u.rdata.check_length);
+                               if (jump == NULL)
+                                       goto fail;
 #ifdef _KERNEL
-                       to_mchain_jump = jump;
+                               to_mchain_jump = jump;
 #else
-                       if (!append_jump(jump, &ret0,
-                           &ret0_size, &ret0_maxsize))
-                               goto fail;
+                               if (!append_jump(jump, &ret0,
+                                   &ret0_size, &ret0_maxsize))
+                                       goto fail;
 #endif
+                       }
                }
 
                pc = &insns[i];
@@ -1491,6 +1508,9 @@
                        if (mode != BPF_ABS && mode != BPF_IND)
                                goto fail;
 
+                       if (unconditional_ret)
+                               continue;
+
                        status = emit_pkt_read(compiler, pc,
                            to_mchain_jump, &ret0, &ret0_size, &ret0_maxsize);
                        if (status != SLJIT_SUCCESS)
@@ -1551,6 +1571,9 @@
                        if (mode != BPF_MSH || BPF_SIZE(pc->code) != BPF_B)
                                goto fail;
 
+                       if (unconditional_ret)
+                               continue;
+
                        status = emit_msh(compiler, pc,
                            to_mchain_jump, &ret0, &ret0_size, &ret0_maxsize);
                        if (status != SLJIT_SUCCESS)