[PATCH] s390: Use long branches across object boundaries (jgh instead of jh)

Carlos O'Donell carlos@redhat.com
Tue Nov 9 19:06:31 GMT 2021


On 11/9/21 12:50, Florian Weimer wrote:
> Depending on the layout chosen by the linker, the 16-bit displacement
> of the jh instruction is insufficient to reach the target label.
> 
> Analysis of the linker failure was carried out by Nick Clifton.
> 
> Tested on a z13 and z15, s390x-linux-gnu only.

Looks correct to me. Converting from BRC to BRCL doubles the available offset bits.
I tested assembling a few variants and they look good to me.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> ---
>  sysdeps/s390/memmem-arch13.S | 2 +-
>  sysdeps/s390/strstr-arch13.S | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/sysdeps/s390/memmem-arch13.S b/sysdeps/s390/memmem-arch13.S
> index c5c8d8c97e..58df8cdb14 100644
> --- a/sysdeps/s390/memmem-arch13.S
> +++ b/sysdeps/s390/memmem-arch13.S
> @@ -41,7 +41,7 @@ ENTRY(MEMMEM_ARCH13)
>  #  error The arch13 variant of memmem needs the z13 variant of memmem!
>  # endif
>  	clgfi	%r5,9
> -	jh	MEMMEM_Z13

OK. jh is BRC (branch relative on condition, A7-M-4-RI) with a 16-bit offset.

> +	jgh	MEMMEM_Z13

OK. jgh is BRCL (branch relative on condition long, C0-M-4-RI) with a 32-bit offset.

>  
>  	aghik	%r0,%r5,-1		/* vll needs highest index.  */
>  	bc	4,0(%r14)		/* cc==1: return if needle-len == 0.  */
> diff --git a/sysdeps/s390/strstr-arch13.S b/sysdeps/s390/strstr-arch13.S
> index c7183e627c..222a6de91a 100644
> --- a/sysdeps/s390/strstr-arch13.S
> +++ b/sysdeps/s390/strstr-arch13.S
> @@ -49,7 +49,7 @@ ENTRY(STRSTR_ARCH13)
>  #  error The arch13 variant of strstr needs the z13 variant of strstr!
>  # endif
>  	clgfi	%r4,9
> -	jh	STRSTR_Z13
> +	jgh	STRSTR_Z13

Likewise.

>  
>  	/* In case of a partial match, the vstrs instruction returns the index
>  	   of the partial match in a vector-register.  Then we have to
> 


-- 
Cheers,
Carlos.



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