On Mon, Apr 24, 2023 at 08:28:55AM -0700, Boqun Feng wrote:
> On Mon, Apr 24, 2023 at 10:13:51AM -0500, Segher Boessenkool wrote:
> > At what points can r13 change? Only when some particular functions are
> > called?
>
> r13 is the local paca:
>
> register struct paca_struct *local_paca asm("r13");
>
> , which is a pointer to percpu data.
Yes, it is a global register variable.
> So if a task schedule from one CPU to anotehr CPU, the value gets
> changed.
But the compiler does not see that something else changes local_paca (or
r13 some other way, via assembler code perhaps)? Or is there a compiler
bug?
If the latter is true:
Can you make a reproducer and open a GCC PR? <https://gcc.gnu.org/bugs/>
for how to get started doing that. We need *exact* code that shows the
problem, together with a compiler command line. So that we can
reproduce the problem. That is step 0 in figuring out what is going on,
and then maybe fixing the problem :-)
Segher
