Zack Weinberg wrote: > Back in 2000 I wrote a really simple patch that caused gcc to treat an > ASM_OPERANDS that clobbered "pc" as a control flow barrier, exactly > for this problem. > > http://gcc.gnu.org/ml/gcc-patches/2000-01/msg00190.html > > I still think it was a good idea, but at the time it was received > unenthusiastically. I especially think "just use __builtin_trap()" > misses the mark - at least some variants of the Linux kernel's BUG() > macro, for instance, want to stick annotations in the assembly stream, > which you cannot do with __builtin_trap...
I agree. Adding options to make __builtin_trap do different things (like generate an abort signal in user applications and something else in kernel mode) is pretty nasty. Linux is a favorite GNU kernel, but there are lots of other kernels out there, and this could get comlicated in a hurry. I think clobbering the PC is a reasonably good way to represent a control-flow barrier at user level. -- Mark Mitchell CodeSourcery [EMAIL PROTECTED] (650) 331-3385 x713
