[MIPS] Add seccomp bpf support

sandbox/linux/seccomp-bpf/syscall_unittest.cc

Index: sandbox/linux/seccomp-bpf/syscall_unittest.cc
diff --git a/sandbox/linux/seccomp-bpf/syscall_unittest.cc b/sandbox/linux/seccomp-bpf/syscall_unittest.cc
index bdeee4fe2da77cf87cbda1d980787e52f3ee93b7..c1b94ff87bae9bbba667c678877af9509cd52f48 100644
--- a/sandbox/linux/seccomp-bpf/syscall_unittest.cc
+++ b/sandbox/linux/seccomp-bpf/syscall_unittest.cc
@@ -15,6 +15,7 @@
 #include "sandbox/linux/seccomp-bpf/bpf_tests.h"
 #include "sandbox/linux/seccomp-bpf/sandbox_bpf.h"
 #include "sandbox/linux/seccomp-bpf/syscall.h"
+#include "sandbox/linux/services/kernel_to_errno.h"
 #include "sandbox/linux/tests/unit_tests.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -50,6 +51,9 @@ TEST(Syscall, WellKnownEntryPoint) {
 #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
@@ -75,7 +79,7 @@ intptr_t CopySyscallArgsToAux(const struct arch_seccomp_data& args, void* aux) {
       static_cast<std::vector<uint64_t>*>(aux);
   BPF_ASSERT(arraysize(args.args) == 6);
   seen_syscall_args->assign(args.args, args.args + arraysize(args.args));
-  return -ENOMEM;
+  return KernelRetToErrno(ENOMEM);
 }
 
 ErrorCode CopyAllArgsOnUnamePolicy(SandboxBPF* sandbox,
@@ -115,7 +119,7 @@ BPF_TEST(Syscall,
                             syscall_args[2],
                             syscall_args[3],
                             syscall_args[4],
-                            syscall_args[5]) == -ENOMEM);
+                            syscall_args[5]) == KernelRetToErrno(ENOMEM));
 
   // We expect the trap handler to have copied the 6 arguments.
   BPF_ASSERT(BPF_AUX->size() == 6);