On 4/15/25 12:01 AM, Alexandre Oliva wrote: > On Apr 14, 2025, Peter Bergner <berg...@linux.ibm.com> wrote: > >> But -mcpu= should not enable -mpowerpc64 by default for -m32 compiles. > > Oh, is that so? It seems to have been the case for quite a long time. > I can trivially see that GCC 9 already did that, but it may have been > around for much longer than that. > > And TBH it seemed sensible to me: if the selected CPU has 64-bit > registers and instructions that use them, why not use them, even when > using a 32-bit ABI? (when one controls the whole system, that is)
To be pedantic, -m32 -mno-powerpc64 and -m32 -mpowerpc64 are different ABIs. The question is, what ABI does the powerpc-elf target use? The same 32-bit ABI as powerpc-linux? If so, that would require not enabling -mpowerpc64 by default for -m32 compiles. You have to be careful using -m32 -mpowerpc64, as that is a specialized use case. You have to know that the kernel you are running on saves and restores the full 64-bit register on context switches. The 32-bit signal contexts will not contain any of the upper 32-bits of the GPR regs. Even calling a library function could corrupt the top part of the callee-saved GPR regs if that library (eg, glibc) is compiled with -m32 -mno-powerpc64. So what ABI does powerpc-elf use and what does it mandate? Peter
