On Mon, Jul 20, 2026 at 05:25:18AM -0500, Segher Boessenkool wrote: > Hi! > > On Mon, Jul 20, 2026 at 12:43:47PM +0530, Saket Kumar Bhaskar wrote: > > In CONFIG_PPC_KERNEL_PCREL mode, r2 is no longer reserved for the TOC > > pointer and is available as a caller-saved register [0]. > > Just like on many more ABIs. Yeah. It's the first that PowerPC Linux > supports though :-) > > > Both call_do_irq() and call_do_softirq() use inline assembly to call > > functions with stack switching, but fail to list r2 in their clobber > > lists. This causes the compiler to assume r2 is preserved across these > > calls, leading to register corruption when the called functions > > (__do_irq and __do_softirq) clobber r2. > > Yeah. > > > index a0e8b998c9b5..26df38bdd334 100644 > > --- a/arch/powerpc/kernel/irq.c > > +++ b/arch/powerpc/kernel/irq.c > > @@ -218,7 +218,12 @@ static __always_inline void call_do_softirq(const void > > *sp) > > [callee] "i" (__do_softirq) > > : // Clobbers > > "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", > > - "cr7", "r0", "r3", "r4", "r5", "r6", "r7", "r8", "r9", "r10", > > + "cr7", "r0", > > + /* r2 is clobbered in PCREL mode */ > > "Note that r2 may be clobbered in the call, when using the ELF V2 ABI"? > > PCREL has nothing to do with it. Well, not directly :-) And the > clobber list does not specify registers that definitely *are* clobbered, > but registers that *may be* clobbered, instead :-) Registers that *are* > clobbered are in the output list (and given a name there so that the new > value can be accessed, etc.) > Thanks for the review. Will send v2 with updated comments as:
r2 may be clobbered by the callee when using the ELFv2 ABI. -Saket > > +#ifdef CONFIG_PPC_KERNEL_PCREL > > + "r2", > > +#endif > > + "r3", "r4", "r5", "r6", "r7", "r8", "r9", "r10", > > "r11", "r12" > > ); > > } > > @@ -276,7 +281,12 @@ static __always_inline void call_do_irq(struct pt_regs > > *regs, void *sp) > > [callee] "i" (__do_irq) > > : // Clobbers > > "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", > > - "cr7", "r0", "r4", "r5", "r6", "r7", "r8", "r9", "r10", > > + "cr7", "r0", > > + /* r2 is clobbered in PCREL mode */ > > +#ifdef CONFIG_PPC_KERNEL_PCREL > > + "r2", > > +#endif > > + "r4", "r5", "r6", "r7", "r8", "r9", "r10", > > "r11", "r12" > > ); > > } > > > Segher
