[PATCH v3 07/12] asm-generic: Define 'func_desc_t' to commonly describe function descriptors

[Nicholas Piggin]

Excerpts from Christophe Leroy's message of October 18, 2021 5:07 pm:
> 
> 
> Le 18/10/2021 à 08:29, Nicholas Piggin a écrit :
>> Excerpts from Christophe Leroy's message of October 17, 2021 10:38 pm:
>>> We have three architectures using function descriptors, each with its
>>> own type and name.
>>>
>>> Add a common typedef that can be used in generic code.
>>>
>>> Also add a stub typedef for architecture without function descriptors,
>>> to avoid a forest of #ifdefs.
>>>
>>> It replaces the similar 'func_desc_t' previously defined in
>>> arch/powerpc/kernel/module_64.c
>>>
>>> Reviewed-by: Kees Cook <keescook at chromium.org>
>>> Acked-by: Arnd Bergmann <arnd at arndb.de>
>>> Signed-off-by: Christophe Leroy <christophe.leroy at csgroup.eu>
>>> ---
>> 
>> [...]
>> 
>>> diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
>>> index a918388d9bf6..33b51efe3a24 100644
>>> --- a/include/asm-generic/sections.h
>>> +++ b/include/asm-generic/sections.h
>>> @@ -63,6 +63,9 @@ extern __visible const void __nosave_begin, __nosave_end;
>>>   #else
>>>   #define dereference_function_descriptor(p) ((void *)(p))
>>>   #define dereference_kernel_function_descriptor(p) ((void *)(p))
>>> +typedef struct {
>>> +	unsigned long addr;
>>> +} func_desc_t;
>>>   #endif
>>>   
>> 
>> I think that deserves a comment. If it's just to allow ifdef to be
>> avoided, I guess that's okay with a comment. Would be nice if you could
>> cause it to generate a link time error if it was ever used like
>> undefined functions, but I guess you can't. It's not a necessity though.
>> 
> 
> I tried to explain it in the commit message, but I can add a comment 
> here in addition for sure.

Thanks.

> 
> By the way, it IS used in powerpc's module_64.c:

Ah yes of course. I guess the point is function descriptors don't exist 
so it should not be used (in general). powerpc module code knows what it
is doing, I guess it's okay for it to use it.

Thanks,
Nick