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Re: Why is _dl_relocate_static_pie linked into crt1.o?


On Thu, Jul 5, 2018 at 5:34 AM, Florian Weimer <fweimer@redhat.com> wrote:
> 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;
> }

Can we fix m68k and arm?

>>> 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.

That is correct.


-- 
H.J.


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