[MIPS] Add seccomp bpf support

sandbox/linux/seccomp-bpf/kernel_return_value_helpers.h

Index: sandbox/linux/seccomp-bpf/kernel_return_value_helpers.h
diff --git a/sandbox/linux/seccomp-bpf/kernel_return_value_helpers.h b/sandbox/linux/seccomp-bpf/kernel_return_value_helpers.h
new file mode 100644
index 0000000000000000000000000000000000000000..117607034eef926ee66370238c90a29e14f49611
--- /dev/null
+++ b/sandbox/linux/seccomp-bpf/kernel_return_value_helpers.h
@@ -0,0 +1,23 @@
+// Copyright 2014 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.
+
+#ifndef SANDBOX_LINUX_SERVICES_KERNEL_RETURN_VALUE_HELPERS_H__

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

Only one trailing "_".

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

I looked in most of the *.h files in seccomp-bpf folder and in all the files
that I looked there are two trailing "_" ...

+#define SANDBOX_LINUX_SERVICES_KERNEL_RETURN_VALUE_HELPERS_H__
+
+#include <signal.h>
+
+namespace sandbox {
+
+// In order for errno to be converted to the value that kernel returns to
+// indicate an error in syscall, errno needs to be negated on Intel/Arm. On
+// Mips this is not the case since Mips has different mechanism for indicating
+// error.
+int ErrnoToKernelRet(int kernel_ret);

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

The argument is an errno, not |kernel_ret|

The documentation for this interface should not mention implementation details
(these should be documented in the .cc file).

// Convert |errno| to the value returned by the kernel when it wants to return
|errno| to userland after a system call.
int ErrnoToKernelRet(int errno);

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

Done.

+
+// The return value from the syscall is written to appropriate register.

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

// Set the registers in |ctx| to match what they would be after a system call
returning |ret_val|.

Also ret_val shouldn't be an int. On a 64 bits architecture, it should be 64
bits. Let's make it an intptr_t?

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

Done.

+void PutValueInUcontext(int ret_val, ucontext_t* ctx);
+
+} // namespace sandbox
+
+#endif  // SANDBOX_LINUX_SERVICES_KERNEL_RETURN_VALUE_HELPERS_H__