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.) > +#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
