Re: [PATCHv2] powerpc64le/power9: guard power9 strcmp against rtld usage [BZ# 25905]

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

On 04/05/2020 12:25, Paul E. Murphy wrote:
> Use rtld-strcpy.S file in power9 to redirect to power8 implementation
> instead.  This builds the power8 strcpy rtld with --with-cpu=power9 and

s/strcpy/strcmp.

> --disable-multi-arch.  The existing behavior is unchanged when
> multi-arch is enabled.

LGTM thanks.

As a side note, is strcmp the only string routine that used in lazy
resolution?

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

> 
> ---8<---
> 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.
> ---
>  sysdeps/powerpc/powerpc64/le/power9/rtld-strcmp.S | 2 ++
>  1 file changed, 2 insertions(+)
>  create mode 100644 sysdeps/powerpc/powerpc64/le/power9/rtld-strcmp.S
> 
> diff --git a/sysdeps/powerpc/powerpc64/le/power9/rtld-strcmp.S b/sysdeps/powerpc/powerpc64/le/power9/rtld-strcmp.S
> new file mode 100644
> index 0000000000..afdb492b3d
> --- /dev/null
> +++ b/sysdeps/powerpc/powerpc64/le/power9/rtld-strcmp.S
> @@ -0,0 +1,2 @@
> +/* Fallback to P8 which does not use vector regs for rtld.  */
> +#include <sysdeps/powerpc/powerpc64/power8/strcmp.S>
>