linux-kernel - Re: [PATCH v1 04/10] asm-generic: Use HAVE_DEREFERENCE_FUNCTION

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Message-ID: <09bcd71a-baae-92b7-4c89-c8d446396d1c@csgroup.eu>
Date:   Tue, 12 Oct 2021 08:11:09 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-ia64@...r.kernel.org, linux-parisc@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 04/10] asm-generic: Use
 HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR to define associated stubs



Le 12/10/2021 à 08:02, Helge Deller a écrit :
> On 10/11/21 17:25, Christophe Leroy wrote:
>> Use HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR instead of 'dereference_function_descriptor'
>> to know whether arch has function descriptors.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>>   arch/ia64/include/asm/sections.h    | 4 ++--
>>   arch/parisc/include/asm/sections.h  | 6 ++++--
>>   arch/powerpc/include/asm/sections.h | 6 ++++--
>>   include/asm-generic/sections.h      | 3 ++-
>>   4 files changed, 12 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/ia64/include/asm/sections.h b/arch/ia64/include/asm/sections.h
>> index 35f24e52149a..80f5868afb06 100644
>> --- a/arch/ia64/include/asm/sections.h
>> +++ b/arch/ia64/include/asm/sections.h
>> @@ -7,6 +7,8 @@
>>    *	David Mosberger-Tang <davidm@....hp.com>
>>    */
>>
>> +#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
>> +
>>   #include <linux/elf.h>
>>   #include <linux/uaccess.h>
>>   #include <asm-generic/sections.h>
>> @@ -27,8 +29,6 @@ extern char __start_gate_brl_fsys_bubble_down_patchlist[], __end_gate_brl_fsys_b
>>   extern char __start_unwind[], __end_unwind[];
>>   extern char __start_ivt_text[], __end_ivt_text[];
>>
>> -#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
>> -
>>   #undef dereference_function_descriptor
>>   static inline void *dereference_function_descriptor(void *ptr)
>>   {
>> diff --git a/arch/parisc/include/asm/sections.h b/arch/parisc/include/asm/sections.h
>> index bb52aea0cb21..2e781ee19b66 100644
>> --- a/arch/parisc/include/asm/sections.h
>> +++ b/arch/parisc/include/asm/sections.h
>> @@ -2,6 +2,10 @@
>>   #ifndef _PARISC_SECTIONS_H
>>   #define _PARISC_SECTIONS_H
>>
>> +#ifdef CONFIG_64BIT
>> +#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
>> +#endif
>> +
>>   /* nothing to see, move along */
>>   #include <asm-generic/sections.h>
>>
>> @@ -9,8 +13,6 @@ extern char __alt_instructions[], __alt_instructions_end[];
>>
>>   #ifdef CONFIG_64BIT
>>
>> -#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
>> -
>>   #undef dereference_function_descriptor
>>   void *dereference_function_descriptor(void *);
>>
>> diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
>> index 32e7035863ac..b7f1ba04e756 100644
>> --- a/arch/powerpc/include/asm/sections.h
>> +++ b/arch/powerpc/include/asm/sections.h
>> @@ -8,6 +8,10 @@
>>
>>   #define arch_is_kernel_initmem_freed arch_is_kernel_initmem_freed
>>
>> +#ifdef PPC64_ELF_ABI_v1
>> +#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
>> +#endif
>> +
>>   #include <asm-generic/sections.h>
>>
>>   extern bool init_mem_is_free;
>> @@ -69,8 +73,6 @@ static inline int overlaps_kernel_text(unsigned long start, unsigned long end)
>>
>>   #ifdef PPC64_ELF_ABI_v1
>>
>> -#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
>> -
>>   #undef dereference_function_descriptor
>>   static inline void *dereference_function_descriptor(void *ptr)
>>   {
>> diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
>> index d16302d3eb59..1db5cfd69817 100644
>> --- a/include/asm-generic/sections.h
>> +++ b/include/asm-generic/sections.h
>> @@ -59,7 +59,8 @@ extern char __noinstr_text_start[], __noinstr_text_end[];
>>   extern __visible const void __nosave_begin, __nosave_end;
>>
>>   /* Function descriptor handling (if any).  Override in asm/sections.h */
>> -#ifndef dereference_function_descriptor
>> +#ifdef HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR
>> +#else
> 
> why not
> #ifndef HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR
> instead of #if/#else ?

To avoid changing it again in patch 6, or getting an ugly #ifndef/#else 
at the end.

> 
>>   #define dereference_function_descriptor(p) ((void *)(p))
>>   #define dereference_kernel_function_descriptor(p) ((void *)(p))
>>   #endif
>>
>