--- /dev/null
+From 91e901c65b4da02a6fd543e3f0049829ae9645b7 Mon Sep 17 00:00:00 2001
+From: Michael Bommarito <michael.bommarito@gmail.com>
+Date: Wed, 8 Apr 2026 03:01:02 -0400
+Subject: um: drivers: call kernel_strrchr() explicitly in cow_user.c
+
+From: Michael Bommarito <michael.bommarito@gmail.com>
+
+commit 91e901c65b4da02a6fd543e3f0049829ae9645b7 upstream.
+
+Building ARCH=um on glibc >= 2.43 fails:
+
+ arch/um/drivers/cow_user.c: error: implicit declaration of
+ function 'strrchr' [-Wimplicit-function-declaration]
+
+glibc 2.43's C23 const-preserving strrchr() macro does not survive
+UML's global -Dstrrchr=kernel_strrchr remap from arch/um/Makefile.
+Call kernel_strrchr() directly in cow_user.c so the source no longer
+depends on the -D rewrite.
+
+Fixes: 2c51a4bc0233 ("um: fix strrchr() problems")
+Suggested-by: Johannes Berg <johannes@sipsolutions.net>
+Cc: stable@vger.kernel.org
+Assisted-by: Claude:claude-opus-4-6
+Assisted-by: Codex:gpt-5-4
+Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
+Link: https://patch.msgid.link/20260408070102.2325572-1-michael.bommarito@gmail.com
+[remove unnecessary 'extern']
+Signed-off-by: Johannes Berg <johannes.berg@intel.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/um/drivers/cow_user.c | 8 +++++++-
+ 1 file changed, 7 insertions(+), 1 deletion(-)
+
+--- a/arch/um/drivers/cow_user.c
++++ b/arch/um/drivers/cow_user.c
+@@ -15,6 +15,12 @@
+ #include "cow.h"
+ #include "cow_sys.h"
+
++/*
++ * arch/um/Makefile remaps strrchr to kernel_strrchr; call the kernel
++ * name directly to avoid glibc >= 2.43's C23 strrchr macro.
++ */
++char *kernel_strrchr(const char *, int);
++
+ #define PATH_LEN_V1 256
+
+ /* unsigned time_t works until year 2106 */
+@@ -153,7 +159,7 @@ static int absolutize(char *to, int size
+ errno);
+ return -1;
+ }
+- slash = strrchr(from, '/');
++ slash = kernel_strrchr(from, '/');
+ if (slash != NULL) {
+ *slash = '\0';
+ if (chdir(from)) {