Hi Rasmus, On Wed, Nov 21, 2018 at 11:05:38AM +0000, Rasmus Villemoes wrote: > I'm trying to build the VxWorks kernel using gcc 7.3. It builds and > boots, but I'm having a problem with use of fpr f0 from interrupt context. > > An ISR ends up calling a function taking an unsigned long long, which is > passed on to another function; the assembly code for shuffling that > argument around is > > 153698: c8 01 00 68 lfd f0,104(r1) > 15369c: d8 01 00 18 stfd f0,24(r1) > > and the first instruction triggers an exception. This is apparently gcc > being clever and using just two instructions for loading/storing 64 > bits. It seems I can avoid the generation of these instructions with > -msoft-float, but that's somewhat of a big hammer, as I do want to use > the FPU for the stuff running in task context. I suppose I could try to > apply -msoft-float just to the TUs that might be called from interrupts, > but what I'm looking for is a switch to avoid using FPRs for integers > (i.e., it's fine to use the FPU when the source code actually works on > floats or doubles). Is there such a switch I'm overlooking? There is no such switch. Implementing such a switch would be hard; for example, the convert-float-to-integer instructions need to store an integer in a floating point register. Compiling translation units with different needs, with different flags, is the way to go. -msoft-float means "do not use the FPRs". Segher
