Re: Why is _dl_relocate_static_pie linked into crt1.o?

[Florian Weimer <fweimer at redhat dot com>]

On 07/05/2018 02:24 PM, Andreas Schwab wrote:
> On Jul 05 2018, Florian Weimer <fweimer@redhat.com> wrote:
>
> > I assume the intent here is that other code can be shared between PIE and
> > non-PIE executables.  However, it's not clear to me why the symbol
> > _dl_relocate_static_pie has to be used in the address calculation.
>
> Which address calculation?

This code in sysdeps/m68k/dl-machine.h (arm has something similar):

/* Return the run-time load address of the shared object.  */
static inline Elf32_Addr
elf_machine_load_address (void)
{
  Elf32_Addr addr;
#ifdef SHARED
  asm (PCREL_OP ("lea", "_dl_start", "%0", "%0", "%%pc") "\n\t"
       "sub.l _dl_start@GOT.w(%%a5), %0"
       : "=a" (addr));
#else
  asm (PCREL_OP ("lea", "_dl_relocate_static_pie", "%0", "%0", "%%pc") 
"\n\t"
       "sub.l _dl_relocate_static_pie@GOT.w(%%a5), %0"
       : "=a" (addr));
#endif
  return addr;
}

> > If there's another symbol which is present in shared and static-PIE
> > builds alike, wouldn't that avoid the need for defining
> > _dl_relocate_static_pie in shared builds?
>
> I don't understand the reference to shared builds.  crt0.o isn't used in
> shared libraries either.

elf_machine_load_address is used in elf/dl-reloc-static-pie.c and in 
elf/rtld.c.  I assume that _dl_relocate_static_pie was stuck into crt1.o 
to satisfy the elf/rtld.c reference.

Thanks,
Florian