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From: Andreas Schwab <schwab@linux-m68k.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: Re: [PATCH] powerpc/64s: power4 nap fixup in C
References: <20210312012044.3660743-1-npiggin@gmail.com>
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X-Yow: I'm an East Side TYPE..
Date: Mon, 29 Mar 2021 13:56:28 +0200
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 (Christophe Leroy's message of "Mon, 29 Mar 2021 11:04:52 +0200")
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Cc: linuxppc-dev@lists.ozlabs.org, Nicholas Piggin <npiggin@gmail.com>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

On Mär 29 2021, Christophe Leroy wrote:

> Le 29/03/2021 à 10:33, Benjamin Herrenschmidt a écrit :
>> On Fri, 2021-03-12 at 11:20 +1000, Nicholas Piggin wrote:
>>>
>>> +static inline void nap_adjust_return(struct pt_regs *regs)
>>>
>>> +{
>>>
>>> +#ifdef CONFIG_PPC_970_NAP
>>>
>>> +       if (unlikely(test_thread_local_flags(_TLF_NAPPING))) {
>>> +               /* Can avoid a test-and-clear because NMIs do not call this */
>>> +               clear_thread_local_flags(_TLF_NAPPING);
>>> +               regs->nip = (unsigned long)power4_idle_nap_return;
>>> +       }
>> Is this a pointer to a function descriptor or the actual code ?
>> 
>
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -209,4 +209,8 @@ _GLOBAL(power4_idle_nap)
>  	mtmsrd	r7
>  	isync
>  	b	1b
> +
> +	.globl power4_idle_nap_return
> +power4_idle_nap_return:
> +	blr
>  #endif

The problem is not the definition, it is the reference.  In C, a
function symbol always resolves to the address of the descriptor.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
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