selftests/nolibc: add tests for multi-object linkage

While uncommon, nolibc executables can be linked together from multiple
compilation units.
Add some tests to make sure everything works in that case.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/lkml/20231012-nolibc-linkage-test-v1-1-315e682768b4@weissschuh.net/Acked-by: Willy Tarreau <w@1wt.eu>

tools/testing/selftests/nolibc/Makefile

@@ -171,17 +171,17 @@ sysroot/$(ARCH)/include:
 	$(Q)mv sysroot/sysroot sysroot/$(ARCH)
 
 ifneq ($(NOLIBC_SYSROOT),0)
-nolibc-test: nolibc-test.c sysroot/$(ARCH)/include
+nolibc-test: nolibc-test.c nolibc-test-linkage.c sysroot/$(ARCH)/include
 	$(QUIET_CC)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ \
-	  -nostdlib -nostdinc -static -Isysroot/$(ARCH)/include $< -lgcc
+	  -nostdlib -nostdinc -static -Isysroot/$(ARCH)/include nolibc-test.c nolibc-test-linkage.c -lgcc
 else
-nolibc-test: nolibc-test.c
+nolibc-test: nolibc-test.c nolibc-test-linkage.c
 	$(QUIET_CC)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ \
-	  -nostdlib -static -include ../../../include/nolibc/nolibc.h $< -lgcc
+	  -nostdlib -static -include ../../../include/nolibc/nolibc.h nolibc-test.c nolibc-test-linkage.c -lgcc
 endif
 
-libc-test: nolibc-test.c
-	$(QUIET_CC)$(HOSTCC) -o $@ $<
+libc-test: nolibc-test.c nolibc-test-linkage.c
+	$(QUIET_CC)$(HOSTCC) -o $@ nolibc-test.c nolibc-test-linkage.c
 
 # local libc-test
 run-libc-test: libc-test

tools/testing/selftests/nolibc/nolibc-test-linkage.c

+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include "nolibc-test-linkage.h"
+
+#ifndef NOLIBC
+#include <errno.h>
+#endif
+
+void *linkage_test_errno_addr(void)
+{
+	return &errno;
+}
+
+int linkage_test_constructor_test_value;
+
+__attribute__((constructor))
+static void constructor1(void)
+{
+	linkage_test_constructor_test_value = 2;
+}
+
+__attribute__((constructor))
+static void constructor2(void)
+{
+	linkage_test_constructor_test_value *= 3;
+}

tools/testing/selftests/nolibc/nolibc-test-linkage.h

+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _NOLIBC_TEST_LINKAGE_H
+#define _NOLIBC_TEST_LINKAGE_H
+
+void *linkage_test_errno_addr(void);
+extern int linkage_test_constructor_test_value;
+
+#endif /* _NOLIBC_TEST_LINKAGE_H */

tools/testing/selftests/nolibc/nolibc-test.c

@@ -41,6 +41,8 @@
 #endif
 #endif
 
+#include "nolibc-test-linkage.h"
+
 /* for the type of int_fast16_t and int_fast32_t, musl differs from glibc and nolibc */
 #define SINT_MAX_OF_TYPE(type) (((type)1 << (sizeof(type) * 8 - 2)) - (type)1 + ((type)1 << (sizeof(type) * 8 - 2)))
 #define SINT_MIN_OF_TYPE(type) (-SINT_MAX_OF_TYPE(type) - 1)
@@ -647,6 +649,8 @@ int run_startup(int min, int max)
 		CASE_TEST(auxv_addr);        EXPECT_PTRGT(test_auxv != (void *)-1, test_auxv, brk); break;
 		CASE_TEST(auxv_AT_UID);      EXPECT_EQ(1, getauxval(AT_UID), getuid()); break;
 		CASE_TEST(constructor);      EXPECT_EQ(1, constructor_test_value, 2); break;
+		CASE_TEST(linkage_errno);    EXPECT_PTREQ(1, linkage_test_errno_addr(), &errno); break;
+		CASE_TEST(linkage_constr);   EXPECT_EQ(1, linkage_test_constructor_test_value, 6); break;
 		case __LINE__:
 			return ret; /* must be last */
 		/* note: do not set any defaults so as to permit holes above */