Memory barriers in userspace? (Linux, x86-64)

Question

It is easy to set memory barriers on the kernel side: the macros mb, wmb, rmb, etc. are always in place thanks to the Linux kernel headers.

How to accomplish this on the user side?

Solution 1

You are looking for the full memory barrier atomic builtins of gcc.

Please note the detail on the reference i gave here says,

The [following] builtins are intended to be compatible with those described in the Intel Itanium Processor-specific Application Binary Interface, section 7.4. As such, they depart from the normal GCC practice of using the “__builtin_” prefix, and further that they are overloaded such that they work on multiple types.

Solution 2

Posix defines a number of functions as acting as memory barriers. Memory locations must not be concurrently accessed; to prevent this, use synchronization - and that synchronization will also work as a barrier.

Solution 3

Use libatomic_ops. http://www.hpl.hp.com/research/linux/atomic_ops/

It's not compiler-specific, and less buggy than the GCC stuff. It's not a giganto-library that provides tons of functionality you don't care about. It just provides atomic operations. Also, it's portable to different CPU architectures.

Solution 4

Linux x64 means you can use the Intel memory barrier instructions. You might wrap them in macros similar to those in the Linux headers, if those macros aren't appropriate or accessible to your code

Solution 5

__sync_synchronize() in GCC 4.4+

The Intel Memory Ordering White Paper, a section from Volume 3A of Intel 64 and IA-32 manual http://developer.intel.com/Assets/PDF/manual/253668.pdf

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