V2 [PATCH v4 06/10] elf: Avoid RELATIVE relocation for _dl_sysinfo

  On Tue, Jan 19, 2021 at 5:51 AM Adhemerval Zanella via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
>
>
> 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)
> >

Like this?
  

On 19/01/2021 11:25, H.J. Lu wrote:
> On Tue, Jan 19, 2021 at 5:51 AM Adhemerval Zanella via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
>>
>>
>>
>> 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)
>>>
> 
> Like this?
> 

> From af3c44826b8ff07082eb5020213652e6b1fadfa4 Mon Sep 17 00:00:00 2001
> From: "H.J. Lu" <hjl.tools@gmail.com>
> Date: Mon, 18 Jan 2021 11:45:46 +0000
> Subject: [PATCH] elf: Avoid RELATIVE relocation for _dl_sysinfo
> 
> Set the default _dl_sysinfo in _dl_aux_init to avoid RELATIVE relocation
> in static PIE.
> 
> This is needed for fixing bug 27072 on x86.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  elf/dl-support.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/elf/dl-support.c b/elf/dl-support.c
> index 384080dd80..7abb65d8e3 100644
> --- a/elf/dl-support.c
> +++ b/elf/dl-support.c
> @@ -199,8 +199,9 @@ int _dl_thread_gscope_count;
>  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;
> +/* Needed for improved syscall handling on at least x86/Linux.  NB: Don't
> +   initialize it here to avoid RELATIVE relocation in static PIE.  */
> +uintptr_t _dl_sysinfo;
>  #endif
>  #ifdef NEED_DL_SYSINFO_DSO
>  /* Address of the ELF headers in the vsyscall page.  */
> @@ -238,6 +239,11 @@ _dl_aux_init (ElfW(auxv_t) *av)
>    uid_t uid = 0;
>    gid_t gid = 0;
>  
> +#ifdef NEED_DL_SYSINFO
> +  /* NB: Avoid RELATIVE relocation in static PIE.  */
> +  GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
> +#endif
> +
>    _dl_auxv = av;
>    for (; av->a_type != AT_NULL; ++av)
>      switch (av->a_type)
> -- 
> 2.29.2