linux-kernel - Re: [PATCH v2 06/13] asm-generic: Use HAVE_FUNCTION

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Message-Id: <1634298613.bp91trt1cz.astroid@bobo.none>
Date:   Fri, 15 Oct 2021 21:52:44 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Helge Deller <deller@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Kees Cook <keescook@...omium.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-arch@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 06/13] asm-generic: Use HAVE_FUNCTION_DESCRIPTORS to
 define associated stubs

Excerpts from Nicholas Piggin's message of October 15, 2021 6:02 pm:
> Excerpts from Christophe Leroy's message of October 15, 2021 4:24 pm:
>> 
>> 
>> Le 15/10/2021 à 08:16, Nicholas Piggin a écrit :
>>> Excerpts from Christophe Leroy's message of October 14, 2021 3:49 pm:
>>>> Replace HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR by
>>>> HAVE_FUNCTION_DESCRIPTORS and use it instead of
>>>> 'dereference_function_descriptor' macro to know
>>>> whether an arch has function descriptors.
>>>>
>>>> To limit churn in one of the following patches, use
>>>> an #ifdef/#else construct with empty first part
>>>> instead of an #ifndef in asm-generic/sections.h
>>> 
>>> Is it worth putting this into Kconfig if you're going to
>>> change it? In any case
>> 
>> That was what I wanted to do in the begining but how can I do that in 
>> Kconfig ?
>> 
>> #ifdef __powerpc64__
>> #if defined(_CALL_ELF) && _CALL_ELF == 2
>> #define PPC64_ELF_ABI_v2
>> #else
>> #define PPC64_ELF_ABI_v1
>> #endif
>> #endif /* __powerpc64__ */
>> 
>> #ifdef PPC64_ELF_ABI_v1
>> #define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> 
> We have ELFv2 ABI / function descriptors iff big-endian so you could 
> just select based on that.

Of course that should read ELFv1. To be clearer: BE is ELFv1 ABI and
LE is ELFv2 ABI.

Thanks,
Nick