[PATCH v2] elf: Add DL_ADDRESS_WITHOUT_RELOC [BZ #33088]

[Florian Weimer]

* Alexander Monakov:

> On Mon, 16 Jun 2025, Florian Weimer wrote:
>
>> * Alexander Monakov:
>> 
>> > On Mon, 16 Jun 2025, Florian Weimer wrote:
>> >
>> >> > @@ -428,7 +429,7 @@ static ElfW(Addr) _dl_start_final (void *arg,
>> >> >  
>> >> >  /* These are defined magically by the linker.  */
>> >> >  extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
>> >> > -extern char _end[] attribute_hidden;
>> >> > +extern char _end attribute_hidden;
>> >> 
>> >> Can you avoid this change (which may have unintended side effects on
>> >> other architectures) if you use
>> >> 
>> >> > +  ({ __typeof (+var) _result = var; asm ("" : "+r"(_result)); _result; })
>> >> 
>> >> in the definition of DL_ADDRESS_WITHOUT_RELOC?
>> >
>> > It won't work, but __auto_type, available since gcc-4.9 and clang-3.8,
>> > will:
>> >
>> >   __auto_type _result = val;
>> >
>> > or something like '__typeof(0 ? val : 0)' can be used for
>> > array-to-pointer decay inside of typeof.
>> 
>> Why doesn't it work?  Shouldn't the + trigger decay from array to
>> pointer?
>
> In C++ it would, but not in C.

Meh.  Awkward.

>> Maybe it needs another one?
>
> Another plus?

Yes, that's what I meant, but I was thinking about asm operand.

But if we can use __auto_type, that's a fine solution.

Thanks,
Florian