Re: [PATCH v4 08/10] csu: Move static pie self relocation later [BZ #27072]

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 19/01/2021 11:35, Szabolcs Nagy wrote:
> The 01/19/2021 11:07, Adhemerval Zanella wrote:
>> On 18/01/2021 13:25, Szabolcs Nagy via Libc-alpha wrote:
>>> IFUNC resolvers may depend on tunables and cpu feature setup so
>>> move static pie self relocation after those.
>>>
>>> It is hard to guarantee that the ealy startup code does not rely
>>> on relocations so this is a bit fragile. It would be more robust
>>> to handle RELATIVE relocs early and only IRELATIVE relocs later,
>>> but the current relocation processing code cannot do that.
>>>
>>> The early startup code before relocation processing includes
>>>
>>>   _dl_aux_init (auxvec);
>>>   __libc_init_secure ();
>>>   __tunables_init (__environ);
>>>   ARCH_INIT_CPU_FEATURES ();
>>>
>>> These are simple enough that RELATIVE relocs can be avoided.
>>>
>>> __ehdr_start may require RELATIVE relocation so it was moved
>>> later, fortunately ehdr and phdr are not used in the early code.
>>>
>>> Fixes bug 27072.
>>
>> LGTM, thanks.
>>
>> Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
> 
> 
> sigh, this is an old version of this patch, i made a
> mistake putting the series together.
> 
> the problem is that _dl_phdr is used in ARCH_SETUP_TLS
> (to get the tls program headers) so the __ehdr_start
> magic should be before that (this only matters if auxv
> lacks AT_PHDR for some reason, which should not happen
> normally on linux, so testing won't show the problem)

By normally do you mean it might happen on a specific kernel version
or is it architecture specific?