[v5,1/5] uapi: Move the aux vector AT_MINSIGSTKSZ define to uapi

  Move the AT_MINSIGSTKSZ definition to generic Linux from arm64. It is
already used as generic ABI in glibc's generic elf.h, and this move will
prevent future namespace conflicts. In particular, x86 will re-use this
generic definition.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>
Cc: Carlos O'Donell <carlos@redhat.com>
Cc: Dave Martin <Dave.Martin@arm.com>
Cc: libc-alpha@sourceware.org
Cc: linux-arch@vger.kernel.org
Cc: linux-api@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
---
Change from v4:
* Added as a new patch (Carlos O'Donell)
---
 arch/arm64/include/uapi/asm/auxvec.h | 1 -
 include/uapi/linux/auxvec.h          | 1 +
 2 files changed, 1 insertion(+), 1 deletion(-)
  

On Wed, Feb 03, 2021 at 09:22:38AM -0800, Chang S. Bae wrote:
> Move the AT_MINSIGSTKSZ definition to generic Linux from arm64. It is
> already used as generic ABI in glibc's generic elf.h, and this move will
> prevent future namespace conflicts. In particular, x86 will re-use this
> generic definition.
> 
> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
> Reviewed-by: Len Brown <len.brown@intel.com>
> Cc: Carlos O'Donell <carlos@redhat.com>
> Cc: Dave Martin <Dave.Martin@arm.com>
> Cc: libc-alpha@sourceware.org
> Cc: linux-arch@vger.kernel.org
> Cc: linux-api@vger.kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> ---
> Change from v4:
> * Added as a new patch (Carlos O'Donell)
> ---
>  arch/arm64/include/uapi/asm/auxvec.h | 1 -
>  include/uapi/linux/auxvec.h          | 1 +
>  2 files changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/uapi/asm/auxvec.h b/arch/arm64/include/uapi/asm/auxvec.h
> index 743c0b84fd30..767d710c92aa 100644
> --- a/arch/arm64/include/uapi/asm/auxvec.h
> +++ b/arch/arm64/include/uapi/asm/auxvec.h
> @@ -19,7 +19,6 @@
>  
>  /* vDSO location */
>  #define AT_SYSINFO_EHDR	33
> -#define AT_MINSIGSTKSZ	51	/* stack needed for signal delivery */

Since this is UAPI, I'm wondering whether we should try to preserve this
definition for users of <asm/auxvec.h>.  (Indeed, it is not uncommon to
include <asm/> headers in userspace hackery, since the <linux/> headers
tend to interact badly with the the libc headers.)

In C11 at least, duplicate #defines are not an error if the definitions
are the same.  I don't know about the history, but I suspect this was
true for older standards too.  So maybe we can just keep this definition
with a duplicate definition in the common header.

Otherwise, we could have

#ifndef AT_MINSIGSTKSZ
#define AT_MINSIGSTKSZ 51
#endif

in include/linux/uapi/auxvec.h, and keep the arm64 header unchanged.

>  
>  #define AT_VECTOR_SIZE_ARCH 2 /* entries in ARCH_DLINFO */
>  
> diff --git a/include/uapi/linux/auxvec.h b/include/uapi/linux/auxvec.h
> index abe5f2b6581b..cc4fa77bd2a7 100644
> --- a/include/uapi/linux/auxvec.h
> +++ b/include/uapi/linux/auxvec.h
> @@ -33,5 +33,6 @@
>  
>  #define AT_EXECFN  31	/* filename of program */
>  
> +#define AT_MINSIGSTKSZ	51	/* stack needed for signal delivery  */
>  
>  #endif /* _UAPI_LINUX_AUXVEC_H */

Otherwise, this looks fine as a concept.

AFAICT, no other arch is already using the value 51.

If nobody else objects to the loss of the definition from arm64's
<asm/auxvec.h> then I guess I can put up with that -- but I will wait to
see if anyone gives a view first.

Cheers
---Dave
  

On Thu, Feb 04, 2021 at 03:55:30PM +0000, Dave Martin wrote:
> On Wed, Feb 03, 2021 at 09:22:38AM -0800, Chang S. Bae wrote:
> > Move the AT_MINSIGSTKSZ definition to generic Linux from arm64. It is
> > already used as generic ABI in glibc's generic elf.h, and this move will
> > prevent future namespace conflicts. In particular, x86 will re-use this
> > generic definition.
> > 
> > Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
> > Reviewed-by: Len Brown <len.brown@intel.com>
> > Cc: Carlos O'Donell <carlos@redhat.com>
> > Cc: Dave Martin <Dave.Martin@arm.com>
> > Cc: libc-alpha@sourceware.org
> > Cc: linux-arch@vger.kernel.org
> > Cc: linux-api@vger.kernel.org
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: linux-kernel@vger.kernel.org
> > ---
> > Change from v4:
> > * Added as a new patch (Carlos O'Donell)
> > ---
> >  arch/arm64/include/uapi/asm/auxvec.h | 1 -
> >  include/uapi/linux/auxvec.h          | 1 +
> >  2 files changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/include/uapi/asm/auxvec.h b/arch/arm64/include/uapi/asm/auxvec.h
> > index 743c0b84fd30..767d710c92aa 100644
> > --- a/arch/arm64/include/uapi/asm/auxvec.h
> > +++ b/arch/arm64/include/uapi/asm/auxvec.h
> > @@ -19,7 +19,6 @@
> >  
> >  /* vDSO location */
> >  #define AT_SYSINFO_EHDR	33
> > -#define AT_MINSIGSTKSZ	51	/* stack needed for signal delivery */
> 
> Since this is UAPI, I'm wondering whether we should try to preserve this
> definition for users of <asm/auxvec.h>.  (Indeed, it is not uncommon to
> include <asm/> headers in userspace hackery, since the <linux/> headers
> tend to interact badly with the the libc headers.)
> 
> In C11 at least, duplicate #defines are not an error if the definitions
> are the same.  I don't know about the history, but I suspect this was
> true for older standards too.  So maybe we can just keep this definition
> with a duplicate definition in the common header.
> 
> Otherwise, we could have
> 
> #ifndef AT_MINSIGSTKSZ
> #define AT_MINSIGSTKSZ 51
> #endif
> 
> in include/linux/uapi/auxvec.h, and keep the arm64 header unchanged.

I think it just boils down to whether or not anything breaks. If it does,
then we'll have to revert the patch, so anything we can do now to minimise
that possibility would be good.

Will