[MIPS] Add seccomp bpf support

sandbox/linux/seccomp-bpf/syscall.h

Index: sandbox/linux/seccomp-bpf/syscall.h
diff --git a/sandbox/linux/seccomp-bpf/syscall.h b/sandbox/linux/seccomp-bpf/syscall.h
index f444d3a36303e52dd1e6498dcded12633b764c90..461ed39bc9f8ac2fd6016dfbd77d9056a02b6129 100644
--- a/sandbox/linux/seccomp-bpf/syscall.h
+++ b/sandbox/linux/seccomp-bpf/syscall.h
@@ -25,6 +25,18 @@ SANDBOX_EXPORT intptr_t SandboxSyscall(int nr,
                                        intptr_t p4,
                                        intptr_t p5);
 
+#if defined(__mips__)
+// This function basically does on MIPS what SandboxSyscall() is doing on
+// othere architectures. However, because of specificity of MIPS regarding
+// handelling syscall errors, SandboxSyscall() is made as a wrapper for this
+// function in order for SandboxSyscall() to behave more like on othere
+// architectures on places where return value from SandboxSyscall() is used
+// directly (like in the most tests).

[jln (very slow on Chromium), 2014/06/03 01:00:33]

"like in most tests"

[nedeljko, 2014/06/03 15:32:18]

Done.

+intptr_t SandboxSyscallRaw(int nr,

[jln (very slow on Chromium), 2014/06/03 01:00:33]

Please, document |args| and |err_stat|

[nedeljko, 2014/06/03 15:32:18]

Done.

+                        const intptr_t *args,

[jln (very slow on Chromium), 2014/06/03 01:00:33]

Nit: chromium style is "type* variable".

[nedeljko, 2014/06/03 15:32:18]

I was looking at the syscall.cc when I wrote this and there is "type *variable"
in use there, but I can see now that this is wrong.

+                        intptr_t *err_stat);
+#endif  // defined(__mips__)
+
 // System calls can take up to six parameters. Traditionally, glibc
 // implements this property by using variadic argument lists. This works, but
 // confuses modern tools such as valgrind, because we are nominally passing