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

[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.

> Maybe it needs another one?

Another plus?

Alexander