[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 10a1253e8c2be65a265665dfc0e7fa2a86208f0f..3105036e50babd611967dc16aed200a8d897bc47 100644
--- a/sandbox/linux/seccomp-bpf/syscall.h
+++ b/sandbox/linux/seccomp-bpf/syscall.h
@@ -5,6 +5,7 @@
 #ifndef SANDBOX_LINUX_SECCOMP_BPF_SYSCALL_H__
 #define SANDBOX_LINUX_SECCOMP_BPF_SYSCALL_H__
 
+#include <signal.h>
 #include <stdint.h>
 
 #include "base/macros.h"
@@ -112,6 +113,11 @@ class SANDBOX_EXPORT Syscall {
     return Call(nr, 0, 0, 0, 0, 0, 0, 0, 0);
   }
 
+  // Set the registers in |ctx| to match what they would be after a system call
+  // returning |ret_val|. |ret_val| must follow the Syscall::Call() convention
+  // of being -errno on errors.
+  static void PutValueInUcontext(intptr_t ret_val, ucontext_t* ctx);
+
  private:
   // This performs system call |nr| with the arguments p0 to p7 from a constant
   // userland address, which is for instance observable by seccomp-bpf filters.
@@ -129,6 +135,21 @@ class SANDBOX_EXPORT Syscall {
                        intptr_t p6,
                        intptr_t p7);
 
+#if defined(__mips__)
+  // This function basically does on MIPS what SandboxSyscall() is doing on
+  // other architectures. However, because of specificity of MIPS regarding
+  // handling syscall errors, SandboxSyscall() is made as a wrapper for this
+  // function in order for SandboxSyscall() to behave more like on other
+  // architectures on places where return value from SandboxSyscall() is used
+  // directly (like in most tests).
+  // The syscall "nr" is called with arguments that are set in an array on which
+  // pointer "args" points to and an information weather there is an error or no
+  // is returned to SandboxSyscall() by err_stat.
+  static intptr_t SandboxSyscallRaw(int nr,
+                                    const intptr_t* args,
+                                    intptr_t* err_stat);
+#endif  // defined(__mips__)
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(Syscall);
 };