[MIPS] Add seccomp bpf support

sandbox/linux/seccomp-bpf/syscall_unittest.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 <asm/unistd.h>
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 
@@ skipping 32 matching lines @@
 #if defined(__i386__)
   EXPECT_EQ(0x80CDu, ((uint16_t*)SandboxSyscall(-1))[-1]);  // INT 0x80
 #elif defined(__x86_64__)
   EXPECT_EQ(0x050Fu, ((uint16_t*)SandboxSyscall(-1))[-1]);  // SYSCALL
 #elif defined(__arm__)
 #if defined(__thumb__)
   EXPECT_EQ(0xDF00u, ((uint16_t*)SandboxSyscall(-1))[-1]);  // SWI 0
 #else
   EXPECT_EQ(0xEF000000u, ((uint32_t*)SandboxSyscall(-1))[-1]);  // SVC 0
 #endif
+#elif defined(__mips__)
+  // Opcode for MIPS sycall is in the lower 16-bits
+  EXPECT_EQ(0x0cu, (((uint32_t *)SandboxSyscall(-1))[-1])&0x0000FFFF);
 #else
 #warning Incomplete test case; need port for target platform
 #endif
 }
 
 TEST(Syscall, TrivialSyscallNoArgs) {
   // Test that we can do basic system calls
   EXPECT_EQ(SandboxSyscall(__NR_getpid), syscall(__NR_getpid));
 }
 
@@ skipping 131 matching lines @@
 
   // Clean up
   EXPECT_EQ(0, SandboxSyscall(__NR_munmap, addr2, 8192L));
   EXPECT_EQ(0, SandboxSyscall(__NR_munmap, addr3, 4096L));
   EXPECT_EQ(0, IGNORE_EINTR(SandboxSyscall(__NR_close, fd)));
 }
 
 }  // namespace
 
 }  // namespace sandbox