[PATCH] s390: Use 64bit branch relative on count instruction in strncpy-z900.S [BZ #34398]

[Stefan Liebler]

At the time the s390-32 strncpy implementation was adjusted for the
s390-64 port, the brct (branch relative on count) instruction was
not adjusted from 32bit to 64bit instruction.

If n contains a value >32bit, the number of 8 byte chunks is computed
with srlg (64bit shift right). The processing of 8 byte chunks is then
processed by looping with brct (32bit branch relative on count) instruction.

This patch just uses the brctg (64bit branch relative on count) instruciton.

Note 1: There is a second loop copying the remaining seven bytes.  The usage
of 32bit brct for looping is fine here.

Note 2: If glibc is build with architecture level set >=z13, the z900 variant
of strncpy is not build at all.

Note 3: If glibc is build for <z13, the z900 ifunc variant is only chosen if
not run on >=z13 or if called via __GI_strncpy.
---
 sysdeps/s390/strncpy-z900.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sysdeps/s390/strncpy-z900.S b/sysdeps/s390/strncpy-z900.S
index 6d954cf402..141cba2294 100644
--- a/sysdeps/s390/strncpy-z900.S
+++ b/sysdeps/s390/strncpy-z900.S
@@ -56,7 +56,7 @@ ENTRY(STRNCPY_Z900)
 	jz    .L10
 	stg   %r0,0(%r2,%r3)	    # store all eight to dest.
 	la    %r3,8(%r3)
-	brct  %r4,.L0
+	brctg %r4,.L0
 .L1:	ltgr  %r1,%r1
 	jz    .Lexit
 .L2:	icm   %r0,1,0(%r3)
-- 
2.54.0