[PATCH v4 06/10] elf: Avoid RELATIVE relocation for _dl_sysinfo

[Adhemerval Zanella]

On 18/01/2021 13:24, Szabolcs Nagy via Libc-alpha wrote:
> From: "H.J. Lu" <hjl.tools@gmail.com>
> 
> In static PIE, set the default _dl_sysinfo in _dl_aux_init, instead of
> using the RELATIVE relocation to intialize it.
> 
> This is needed for fixing bug 27072 on x86.
> ---
>  elf/dl-support.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/elf/dl-support.c b/elf/dl-support.c
> index 384080dd80..5acd59290f 100644
> --- a/elf/dl-support.c
> +++ b/elf/dl-support.c
> @@ -200,7 +200,12 @@ struct dl_scope_free_list *_dl_scope_free_list;
>  
>  #ifdef NEED_DL_SYSINFO
>  /* Needed for improved syscall handling on at least x86/Linux.  */
> -uintptr_t _dl_sysinfo = DL_SYSINFO_DEFAULT;
> +uintptr_t _dl_sysinfo
> +/* NB: Avoid RELATIVE relocation in static PIE.  */
> +# ifndef BUILD_PIE_DEFAULT
> +  = DL_SYSINFO_DEFAULT
> +# endif
> +;
>  #endif
>  #ifdef NEED_DL_SYSINFO_DSO
>  /* Address of the ELF headers in the vsyscall page.  */
> @@ -238,6 +243,11 @@ _dl_aux_init (ElfW(auxv_t) *av)
>    uid_t uid = 0;
>    gid_t gid = 0;
>  
> +#if defined NEED_DL_SYSINFO && BUILD_PIE_DEFAULT
> +  /* NB: Avoid RELATIVE relocation in static PIE.  */
> +  GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
> +#endif
> +

Couldn't we make it the default instead? 

>    _dl_auxv = av;
>    for (; av->a_type != AT_NULL; ++av)
>      switch (av->a_type)
>