Hi Koakuma. On Sat, Mar 23, 2024 at 04:37:27PM +0000, Koakuma wrote: > 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. I tried to build a sparc32 kernel with the two -fcall-used-g5 -fcall-used-g7 flags dropped. Everything worked for me in qemu - but then I only booted to a prompt and browsed around a little. >From your explanation and our limited testing it seems likely the flags can be dropped, but I cannot say for sure. Unless others chime in maybe try to send in patches to drop the flags from sparc32 and sparc64 and see how it goes. Sam
