On Tue, Oct 23, 2012 at 14:28:46 +0200, Tim Blechmann wrote:
however on debian for example, the compiler defaults to generate code for i486. cmpxchg8b has been introduced with the p5 architecture, though, so compiling without specifying a -march flag won't generate the instruction.
GCC will not let you use instructions outside of the target architecture.
fyi, boost.atomic is using inline assembly
While inline assembly may allow to circumvent that restriction, I do not think it is a good idea to force a design that requires their usage.
in a perfect world, we would not need boost.atomic, as all compilers, standard libraries would be c++11 compliant.
helge might want to comment about his decision to use inline assembly, but iirc, gcc did not provide good support for atomic builtins until 4.4 or so ... so portability would be a reason
gcc __sync functions were introduced in gcc 4.1. Some of them were introduced later, but __sync_val_compare_and_swap is there from the start. Developing for mobile platforms and thus non-intel architectures, I would really prefer if boost used the __sync operations whenever available. That would cover non-ancient gcc targeting either ancient (the Debian case) or esoteric (the embedded case) CPUs. -- Jan 'Bulb' Hudec <bulb@ucw.cz>