On Sat, Dec 07, 2019 at 10:42:28AM +0100, Christophe Leroy wrote: > Le 06/12/2019 à 21:59, Segher Boessenkool a écrit : > >If the compiler can see the callee wants the same TOC as the caller has, > >it does not arrange to set (and restore) it, no. If it sees it may be > >different, it does arrange for that (and the linker then will check if > >it actually needs to do anything, and do that if needed). > > > >In this case, the compiler cannot know the callee wants the same TOC, > >which complicates thing a lot -- but it all works out. > > Do we have a way to make sure which TOC the functions are using ? Is > there several TOC at all in kernel code ?
Kernel modules have their own TOC, I think? > >I think things can still go wrong if any of this is inlined into a kernel > >module? Is there anything that prevents this / can this not happen for > >some fundamental reason I don't see? > > This can't happen can it ? > do_softirq_own_stack() is an outline function, defined in powerpc irq.c > Its only caller is do_softirq() which is an outline function defined in > kernel/softirq.c > > That prevents inlining, doesn't it ? Hopefully, sure. Would be nice if it was clearer that this works... It is too much like working by chance, the way it is :-( > Anyway, until we clarify all this I'll limit my patch to PPC32 which is > where the real benefit is I guess. > > At the end, maybe the solution should be to switch to IRQ stack > immediately in the exception entry as x86_64 do ? > > And do_softirq_own_stack() could be entirely written in assembly like > x86_64 as well ? Maybe? I'm out of my depth there. Segher
