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SubjectRe: [PATCH 1/1] arch/powerpc: Rework local_paca to avoid LTO warnings
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"Alastair D'Silva" <alastair@au1.ibm.com> writes:

> From: Alastair D'Silva <alastair@d-silva.org>
>
> When building an LTO kernel, the existing code generates warnings:
> ./arch/powerpc/include/asm/paca.h:37:30: warning: register of
> ‘local_paca’ used for multiple global register variables
> register struct paca_struct *local_paca asm("r13");
> ^
> ./arch/powerpc/include/asm/paca.h:37:30: note: conflicts with
> ‘local_paca’
>
> This patch reworks local_paca into an inline getter & setter function,
> which addresses the warning.
>
> Generated ASM from this patch is broadly similar (addresses have
> changed and the compiler uses different GPRs in some places).

Ditto to Christophe's comment; I'd love to know how to build this so I
can actually see the differences. Perhaps you could bundle up all the
required changes and send it as a patch series with a cover letter
explaining this?

> +static inline struct paca_struct *get_paca_no_preempt_check(void)
> +{
> + register struct paca_struct *paca asm("r13");
> + return paca;
> +}

Isn't the convention to have the { on the same line as the function, or
am I horrible mis-remembering things?

Should these functions be __always_inline?

Regards,
Daniel

> +
> +static inline struct paca_struct *get_paca(void)
> +{
> +#if defined(CONFIG_DEBUG_PREEMPT) && defined(CONFIG_SMP)
> + /*
> + * Add standard checks that preemption cannot occur when using get_paca():
> + * otherwise the paca_struct it points to may be the wrong one just after.
> + */
> + debug_smp_processor_id();
> +#endif
> + return get_paca_no_preempt_check();
> +}
> +
> +#define local_paca get_paca_no_preempt_check()
> +
> +static inline void set_paca(struct paca_struct *new)
> +{
> + register struct paca_struct *paca asm("r13");
> + paca = new;
> +}
> +
> +
> extern void copy_mm_to_paca(struct mm_struct *mm);
> extern struct paca_struct **paca_ptrs;
> extern void initialise_paca(struct paca_struct *new_paca, int cpu);
> diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
> index 913bfca09c4f..ae5c243f9d5a 100644
> --- a/arch/powerpc/kernel/paca.c
> +++ b/arch/powerpc/kernel/paca.c
> @@ -172,7 +172,7 @@ void __init initialise_paca(struct paca_struct *new_paca, int cpu)
> void setup_paca(struct paca_struct *new_paca)
> {
> /* Setup r13 */
> - local_paca = new_paca;
> + set_paca(new_paca);
>
> #ifdef CONFIG_PPC_BOOK3E
> /* On Book3E, initialize the TLB miss exception frames */
> --
> 2.20.1

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