Re: [PATCH] powerpc64le/power9: guard power9 strcmp against rtld usage [BZ# 25905]

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

On 01/05/2020 17:32, Paul E. Murphy via Libc-alpha wrote:
> strcmp is used while resolving PLT references.  Vector registers
> should not be used during this.  The P9 strcmp makes heavy use of
> vector registers, so it should be avoided in rtld.
> 
> This prevents quiet vector register corruption when glibc is configured
> with --disable-multi-arch and --with-cpu=power9.  This can be seen with
> test-float64x-compat_totalordermag during the first call into
> totalordermagf64x@GLIBC_2.27.
> 
> Add a guard to fallback to the power8 implementation when building
> power9 strcmp for libraries other than libc.

The more usual way and it has the advantages of decouple the generic
implementation and make it more explicit is to add a new rtld-strcmp.S
file:

$ cat sysdeps/powerpc/powerpc64/le/power9/rtld-strcmp.S
#include <sysdeps/powerpc/powerpc64/power8/strcmp.S>


> ---
>  sysdeps/powerpc/powerpc64/le/power9/strcmp.S | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/sysdeps/powerpc/powerpc64/le/power9/strcmp.S b/sysdeps/powerpc/powerpc64/le/power9/strcmp.S
> index 412a13599d..b29ea7c020 100644
> --- a/sysdeps/powerpc/powerpc64/le/power9/strcmp.S
> +++ b/sysdeps/powerpc/powerpc64/le/power9/strcmp.S
> @@ -17,6 +17,11 @@
>     <https://www.gnu.org/licenses/>.  */
>  #include <sysdep.h>
>  
> +#if !IS_IN(libc)
> +/* Fallback to P8 which does not use vector regs for rtld.  */
> +#include <sysdeps/powerpc/powerpc64/power8/strcmp.S>
> +#else
> +
>  #ifndef STRCMP
>  # define STRCMP strcmp
>  #endif
> @@ -262,3 +267,5 @@ L(pagecross_nullfound):
>  	b	L(pagecross_retdiff)
>  END (STRCMP)
>  libc_hidden_builtin_def (strcmp)
> +
> +#endif
>