On Fri, Sep 02, 2022 at 10:57:27AM -0500, Peter Bergner wrote: > On 8/31/22 5:45 PM, Segher Boessenkool wrote: > > Yes, this is guaranteed. > > Agree with Segher here. That said, there was a gcc bug a looooong time > ago where gcc copied r13 into a temporary register and used it from there.
r13 is a fixed register on most of our ABIs (everything that is not AIX or Darwin, even), so this can never happen. Except if there are bugs, of course ;-) > That's ok (correctness wise, but not ideal) from user land standpoint, > but we took a context switch after the reg copy and it was restarted on > a different cpu, so differnt local_paca and r13 value. We went boom > because the copy wasn't pointing to the correct local_paca anymore. > So it is very important the compiler always use r13 when accessing > the local_paca. Yes. So we either whould use -ffixed-r13, or just not use unsupported compilers. powerpc*-linux and powerpc*-elf work fine for example :-) Segher
