commit 9b7651410375ec8848a1944992d663d514db4ba7
Author: Stefan Liebler <stli@linux.ibm.com>
Date:   Thu Jul 11 11:28:53 2024 +0200

    s390x: Fix segfault in wcsncmp [BZ #31934]
    
    The z13/vector-optimized wcsncmp implementation segfaults if n=1
    and there is only one character (equal on both strings) before
    the page end.  Then it loads and compares one character and misses
    to check n again.  The following load fails.
    
    This patch removes the extra load and compare of the first character
    and just start with the loop which uses vector-load-to-block-boundary.
    This code-path also checks n.
    
    With this patch both tests are passing:
    - the simplified one mentioned in the bugzilla 31934
    - the full one in Florian Weimer's patch:
    "manual: Document a GNU extension for strncmp/wcsncmp"
    (https://patchwork.sourceware.org/project/glibc/patch/874j9eml6y.fsf@oldenburg.str.redhat.com/):
    On s390x-linux-gnu (z16), the new wcsncmp test fails due to bug 31934.
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>

diff --git a/sysdeps/s390/wcsncmp-vx.S b/sysdeps/s390/wcsncmp-vx.S
index bf6dfa6bc2..8b081567a2 100644
--- a/sysdeps/s390/wcsncmp-vx.S
+++ b/sysdeps/s390/wcsncmp-vx.S
@@ -59,14 +59,7 @@ ENTRY(WCSNCMP_Z13)
 	sllg	%r4,%r4,2	/* Convert character-count to byte-count.  */
 	locgrne	%r4,%r1		/* Use max byte-count, if bit 0/1 was one.  */
 
-	/* Check first character without vector load.  */
-	lghi	%r5,4		/* current_len = 4 bytes.  */
-	/* Check s1/2[0].  */
-	lt	%r0,0(%r2)
-	l	%r1,0(%r3)
-	je	.Lend_cmp_one_char
-	crjne	%r0,%r1,.Lend_cmp_one_char
-
+	lghi	%r5,0		/* current_len = 0 bytes.  */
 .Lloop:
 	vlbb	%v17,0(%r5,%r3),6 /* Load s2 to block boundary.  */
 	vlbb	%v16,0(%r5,%r2),6 /* Load s1 to block boundary.  */
@@ -167,7 +160,6 @@ ENTRY(WCSNCMP_Z13)
 	srl	%r4,2		/* And convert it to character-index.  */
 	vlgvf	%r0,%v16,0(%r4)	/* Load character-values.  */
 	vlgvf	%r1,%v17,0(%r4)
-.Lend_cmp_one_char:
 	cr	%r0,%r1
 	je	.Lend_equal
 	lghi	%r2,1