https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82602
--- Comment #7 from David Brown <david at westcontrol dot com> --- (In reply to Xi Ruoyao from comment #3) There is no intention to make "asm volatile" a barrier, as you get with a memory clobber. The intention is to stop it moving past other volatile code (such as other asm volatiles, and volatile memory accesses). An "asm volatile" statement should still be moveable across other "normal" code. (In reply to Xi Ruoyao from comment #4) As for the comment in the kernel code, the gcc documentation says that an "asm" statement with no output is automatically considered as though it were "asm volatile". So it should not be necessary to write "volatile" in the memory barrier here, as the compiler should treat it that way anyway. If there is a compiler bug there, it should be fixed - or the documentation could be changed. There is certainly no harm in having the "volatile" explicit in the barrier() definition.
