[PATCH v2 2/2] lib: make a test module with set/clear bit

[Jesse Brandeburg]

Test some bit clears/sets to make sure assembly doesn't change.
Instruct Kbuild to build this file with extra warning level -Wextra,
to catch new issues, and also doesn't hurt to build with C=1.

This was used to test changes to arch/x86/include/asm/bitops.h.

Recommended usage:
make defconfig
scripts/config -m CONFIG_TEST_BITOPS
make modules_prepare
make C=1 W=1 lib/test_bitops.ko
objdump -S -d lib/test_bitops.ko

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>
---
v2: use correct CC: list
---
 lib/Kconfig.debug                  | 13 ++++++++++++
 lib/Makefile                       |  2 ++
 lib/test_bitops.c                  | 34 ++++++++++++++++++++++++++++++
 tools/testing/selftests/lib/config |  1 +
 4 files changed, 50 insertions(+)
 create mode 100644 lib/test_bitops.c

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 69def4a9df00..61a5d00ea064 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1947,6 +1947,19 @@ config TEST_LKM
 
 	  If unsure, say N.
 
+config TEST_BITOPS
+	tristate "Test module for compilation of clear_bit/set_bit operations"
+	depends on m
+	help
+	  This builds the "test_bitops" module that is much like the
+	  TEST_LKM module except that it does a basic exercise of the
+	  clear_bit and set_bit macros to make sure there are no compiler
+	  warnings from C=1 sparse checker or -Wextra compilations. It has
+	  no dependencies and doesn't run or load unless explicitly requested
+	  by name.  for example: modprobe test_bitops.
+
+	  If unsure, say N.
+
 config TEST_VMALLOC
 	tristate "Test module for stress/performance analysis of vmalloc allocator"
 	default n
diff --git a/lib/Makefile b/lib/Makefile
index 611872c06926..b18db565b355 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -89,6 +89,8 @@ obj-$(CONFIG_TEST_OBJAGG) += test_objagg.o
 obj-$(CONFIG_TEST_STACKINIT) += test_stackinit.o
 obj-$(CONFIG_TEST_BLACKHOLE_DEV) += test_blackhole_dev.o
 obj-$(CONFIG_TEST_MEMINIT) += test_meminit.o
+obj-$(CONFIG_TEST_BITOPS) += test_bitops.o
+CFLAGS_test_bitops.o += -Werror
 
 obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/
 
diff --git a/lib/test_bitops.c b/lib/test_bitops.c
new file mode 100644
index 000000000000..077af86cf616
--- /dev/null
+++ b/lib/test_bitops.c
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+
+/* a tiny module only meant to compile-test set/clear_bit */
+
+static DECLARE_BITMAP(g_bitmap, 80);
+
+static int __init test_bitops_startup(void)
+{
+	pr_warn("Loaded test module\n");
+	set_bit(4, g_bitmap);
+	set_bit(11, g_bitmap);
+	set_bit(40, g_bitmap);
+	return 0;
+}
+
+static void __exit test_bitops_unstartup(void)
+{
+	clear_bit(4, g_bitmap);
+	clear_bit(11, g_bitmap);
+	clear_bit(40, g_bitmap);
+	pr_warn("Unloaded test module\n");
+}
+
+module_init(test_bitops_startup);
+module_exit(test_bitops_unstartup);
+
+MODULE_AUTHOR("Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Bit testing module");
diff --git a/tools/testing/selftests/lib/config b/tools/testing/selftests/lib/config
index 14a77ea4a8da..b80ee3f6e265 100644
--- a/tools/testing/selftests/lib/config
+++ b/tools/testing/selftests/lib/config
@@ -2,3 +2,4 @@ CONFIG_TEST_PRINTF=m
 CONFIG_TEST_BITMAP=m
 CONFIG_PRIME_NUMBERS=m
 CONFIG_TEST_STRSCPY=m
+CONFIG_TEST_BITOPS=m
-- 
2.24.1