[MIPS] Add seccomp bpf support

sandbox/linux/seccomp-bpf/syscall_iterator.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sandbox/linux/seccomp-bpf/syscall_iterator.h"
 
 #include "base/basictypes.h"
 #include "sandbox/linux/seccomp-bpf/linux_seccomp.h"
 
 namespace sandbox {
 
 uint32_t SyscallIterator::Next() {
   if (done_) {
     return num_;
   }
 
   uint32_t val;
   do {
+#if defined(__mips__) && (_MIPS_SIM == _MIPS_SIM_ABI32)
+    // |num_| has been initialized to 4000, which we assume is also MIN_SYSCALL.
+    // This is true for Mips O32 ABI.
+    COMPILE_ASSERT(MIN_SYSCALL == __NR_Linux, min_syscall_should_be_4000);

[jln (very slow on Chromium), 2014/05/02 20:42:04]

The syscall iterator should always start at 0, this is why this compile assert
was here.
So, in the constructor, keep initializing num_ to 0.

Here, do something similar to the version in this CL:
https://chromiumcodereview.appspot.com/11096012/diff/1/sandbox/linux/seccomp-...

i.e. if MIN_SYSCALL is not 0, the iterator should first return MIN_SYSCALL -1
before continuing to iterate.

[nedeljko, 2014/05/07 15:40:05]

I initialized num_ to 0 in constructor in new patch.
However this assert checks value of MIN_SYSCALL and on MIPS this value is not
zero.

+#else
     // |num_| has been initialized to 0, which we assume is also MIN_SYSCALL.
     // This true for supported architectures (Intel and ARM EABI).
     COMPILE_ASSERT(MIN_SYSCALL == 0u, min_syscall_should_always_be_zero);
+#endif
     val = num_;
 
     // First we iterate up to MAX_PUBLIC_SYSCALL, which is equal to MAX_SYSCALL
     // on Intel architectures, but leaves room for private syscalls on ARM.
     if (num_ <= MAX_PUBLIC_SYSCALL) {
       if (invalid_only_ && num_ < MAX_PUBLIC_SYSCALL) {
         num_ = MAX_PUBLIC_SYSCALL;
       } else {
         ++num_;
       }
@@ skipping 51 matching lines @@
 #if defined(__arm__) && (defined(__thumb__) || defined(__ARM_EABI__))
 bool SyscallIterator::IsArmPrivate(uint32_t num) {
   return (num >= MIN_PRIVATE_SYSCALL && num <= MAX_PRIVATE_SYSCALL) ||
          (num >= MIN_GHOST_SYSCALL && num <= MAX_SYSCALL);
 }
 #else
 bool SyscallIterator::IsArmPrivate(uint32_t) { return false; }
 #endif
 
 }  // namespace sandbox