How to perform atomic operations on Linux that work on x86, arm, GCC and icc?

Question

Every Modern OS provides today some atomic operations:

• Windows has Interlocked* API
• FreeBSD has

Answer 1

__sync* certainly is (and has been) supported by the Intel compiler, because GCC adopted these build-ins from there. Read the first paragraph on this page. Also see "Intel® C++ Compiler for Linux* Intrinsics Reference", page 198. It's from 2006 and describes exactly those built-ins.

Regarding ARM support, for older ARM CPUs: it cannot be done entirely in userspace, but it can be done in kernelspace (by disabling interrupts during the operation), and I think I read somewhere that it is supported for quite a while now.

According to this PHP bug, dated 2011-10-08, __sync_* will only fail on

• PA-RISC with anything other than Linux
• SPARCv7 and lower
• ARM with GCC < 4.3
• ARMv5 and lower with anything other than Linux
• MIPS1

So with GCC > 4.3 (and 4.7 is the current one), you shouldn't have a problem with ARMv6 and newer. You shouldn't have no problem with ARMv5 either as long as compiling for Linux.