Hello Sam, Sam Ravnborg <sam@xxxxxxxxxxxx> wrote: > Hi Koakuma, > Looking at https://github.com/gcc-mirror/gcc/blob/master/gcc/config/sparc/sparc.h > I read that: > > On v9 systems: > g1,g5 are free to use as temporaries, and are free to use between calls > ... > g6-g7 are reserved for the operating system (or application in > embedded case). > > Based on the above I would assume gcc do not change behaviour with or > without -fcall-used-g7. > [...] > For sparc32 the above file says: > > g5 through g7 are reserved for the operating system. > > So again - it looks like -fcall-used-g5 -fcall-used-g7 should have no > effect here and verification on a real target would be nice. > > Sam >From my understanding (and looking at the codegen results) those flags forces GCC to treat the named register as volatile, despite what the ABI says. However, I also believe that removing them wouldn't be harmful? To quote my reasoning in the LLVM tracker: > omitting the flags shouldn't be harmful either - compilers will now > simply refuse to touch them, and any assembly code that happens > to touch them would still work like usual (because Linux' conventions > already treats them as volatile anyway). But I am not entirely sure about it, that is why it'd be great if there's some explaination on why those flags were added in the first place. > I do not have a sparc64 system at my hands - and for this qemu may not > cut it. But it would be super if someone with a working sparc64 target > could verify if the kernel could be built and works without > -fcall-used-g7. I am currently running a build with those flags taken out on a T5120, and the kernel seems to be running okay for what I do (LLVM development), but I don't know if there are more comprehensive test suite for me to try on.
