selftests: mptcp: Mark xerror and die_perror __noreturn

Compiler reports potential uses of uninitialized variables in
mptcp_connect.c when xerror() is called from failure paths.

mptcp_connect.c:1262:11: warning: variable 'raw_addr' is used
      uninitialized whenever 'if' condition is false
      [-Wsometimes-uninitialized]

xerror() terminates execution by calling exit(), but it is not visible
to the compiler & assumes control flow may continue past the call.

Annotate xerror() with __noreturn so the compiler can correctly reason
about control flow and avoid false-positive uninitialized variable
warnings.

Signed-off-by: Ankit Khushwaha <ankitkhushwaha.linux@gmail.com>
Link: https://patch.msgid.link/20260101172840.90186-1-ankitkhushwaha.linux@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/mptcp/Makefile

@@ -3,6 +3,7 @@
 top_srcdir = ../../../../..
 
 CFLAGS += -Wall -Wl,--no-as-needed -O2 -g -I$(top_srcdir)/usr/include $(KHDR_INCLUDES)
+CFLAGS += -I$(top_srcdir)/tools/include
 
 TEST_PROGS := \
 	diag.sh \

tools/testing/selftests/net/mptcp/mptcp_connect.c

@@ -33,6 +33,7 @@
 #include <linux/tcp.h>
 #include <linux/time_types.h>
 #include <linux/sockios.h>
+#include <linux/compiler.h>
 
 extern int optind;
 
@@ -140,7 +141,7 @@ static void die_usage(void)
 	exit(1);
 }
 
-static void xerror(const char *fmt, ...)
+static void __noreturn xerror(const char *fmt, ...)
 {
 	va_list ap;
 

tools/testing/selftests/net/mptcp/mptcp_diag.c

@@ -5,6 +5,7 @@
 #include <linux/rtnetlink.h>
 #include <linux/inet_diag.h>
 #include <linux/netlink.h>
+#include <linux/compiler.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <linux/tcp.h>
@@ -87,7 +88,7 @@ enum {
 
 #define rta_getattr(type, value)		(*(type *)RTA_DATA(value))
 
-static void die_perror(const char *msg)
+static void __noreturn die_perror(const char *msg)
 {
 	perror(msg);
 	exit(1);

tools/testing/selftests/net/mptcp/mptcp_inq.c

@@ -28,6 +28,7 @@
 
 #include <linux/tcp.h>
 #include <linux/sockios.h>
+#include <linux/compiler.h>
 
 #ifndef IPPROTO_MPTCP
 #define IPPROTO_MPTCP 262
@@ -40,7 +41,7 @@ static int pf = AF_INET;
 static int proto_tx = IPPROTO_MPTCP;
 static int proto_rx = IPPROTO_MPTCP;
 
-static void die_perror(const char *msg)
+static void __noreturn die_perror(const char *msg)
 {
 	perror(msg);
 	exit(1);
@@ -52,7 +53,7 @@ static void die_usage(int r)
 	exit(r);
 }
 
-static void xerror(const char *fmt, ...)
+static void __noreturn xerror(const char *fmt, ...)
 {
 	va_list ap;
 

tools/testing/selftests/net/mptcp/mptcp_sockopt.c

@@ -25,6 +25,7 @@
 #include <netinet/in.h>
 
 #include <linux/tcp.h>
+#include <linux/compiler.h>
 
 static int pf = AF_INET;
 
@@ -127,7 +128,7 @@ struct so_state {
 #define MIN(a, b) ((a) < (b) ? (a) : (b))
 #endif
 
-static void die_perror(const char *msg)
+static void __noreturn die_perror(const char *msg)
 {
 	perror(msg);
 	exit(1);
@@ -139,7 +140,7 @@ static void die_usage(int r)
 	exit(r);
 }
 
-static void xerror(const char *fmt, ...)
+static void __noreturn xerror(const char *fmt, ...)
 {
 	va_list ap;