On 5/5/21 4:45 AM, Thorsten Glaser wrote: > Dixi quod… > >> Jessica Clarke brought out docs saying f8‥f15 must be saved, the >> other FPU registers not:
I can confirm this. It is f8-f15 for the z/Architecture (64 bit). It is f1, f3, f5, f7 for the ESA architecture (32 bit) which is still supported by Glibc and GCC. > > This needs to be fixed in klibc. > >>> • klibc does not really support the FPU anyway >> >> … GCC chooses to allocate an FPU register for a pointer value. GCC will put integer values into vector registers for auto-vectorization or for spilling. We also use call-clobbered FPRs as save slots for GPRs in leaf-functions if can get rid of allocating a stack frame that way. > > This is a curiosity. > >>> • the half of v10 that equals f10 just HAPPENS to be saved by >>> glibc, but what if the upper half, that is outside of the FPU, >>> is used? >> >> The question here is, does GCC only use the halves of the half >> of the vector registers that match the FPU registers? > > 04:41⎜«jrtc27:#debian-x32» hephaistor: re s390x vector registers, reading the > gcc and llvm sources they're > ⎜ all call-clobbered by default, only the float parts are call-saved > 04:41⎜«jrtc27:#debian-x32» so that's why setjmp/longjmp don't need to > save/restore them > 04:42⎜«jrtc27:#debian-x32» there *is* a vector calling convention, but it's > not the default for the ABI, > ⎜ it's opt-in, and setjmp/longjmp won't be annotated as such > > So we indeed need to only save the registers glibc does. The vector registers are call-clobbered - exactly for the reason of setjmp / longjmp. Only f8-f15 need to be saved. You can find the latest version of our ABI here: https://github.com/IBM/s390x-abi/releases/download/v1.5/lzsabi_s390x.pdf However, it is still lacking the vector ABI extension. I wrote a document for that which we use internally and we are working on integrating it into the publicly available version. Andreas > >> @klibc list: as indicated earlier, I can provide a patch if needed >> (though it should be obvious). > > bye, > //mirabilos >
