lib: make a test module with set/clear bit

Test some bit clears/sets to make sure assembly doesn't change, and that
the set_bit and clear_bit functions work and don't cause sparse warnings.

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.

In particular, sparse (C=1) was very concerned when the last bit before a
natural boundary, like 7, or 31, was being tested, as this causes sign
extension (0xffffff7f) for instance when clearing bit 7.

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
  insmod lib/test_bitops.ko
  rmmod lib/test_bitops.ko

<check dmesg>, there should be no compiler/sparse warnings and no
error messages in log.

Link: http://lkml.kernel.org/r/20200310221747.2848474-2-jesse.brandeburg@intel.com
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
CcL Ingo Molnar <mingo@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jesse Brandeburg 2020-06-04 16:50:27 -07:00 committed by Linus Torvalds
parent 63d7f8167f
commit c348c16305
4 changed files with 76 additions and 0 deletions

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@ -2022,6 +2022,19 @@ 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

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@ -56,6 +56,8 @@ obj-y += kstrtox.o
obj-$(CONFIG_FIND_BIT_BENCHMARK) += find_bit_benchmark.o
obj-$(CONFIG_TEST_BPF) += test_bpf.o
obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
obj-$(CONFIG_TEST_BITOPS) += test_bitops.o
CFLAGS_test_bitops.o += -Werror
obj-$(CONFIG_TEST_SYSCTL) += test_sysctl.o
obj-$(CONFIG_TEST_HASH) += test_hash.o test_siphash.o
obj-$(CONFIG_TEST_IDA) += test_ida.o

60
lib/test_bitops.c Normal file
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@ -0,0 +1,60 @@
// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2020 Intel Corporation
*/
#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 test set/clear_bit */
/* use an enum because thats the most common BITMAP usage */
enum bitops_fun {
BITOPS_4 = 4,
BITOPS_7 = 7,
BITOPS_11 = 11,
BITOPS_31 = 31,
BITOPS_88 = 88,
BITOPS_LAST = 255,
BITOPS_LENGTH = 256
};
static DECLARE_BITMAP(g_bitmap, BITOPS_LENGTH);
static int __init test_bitops_startup(void)
{
pr_warn("Loaded test module\n");
set_bit(BITOPS_4, g_bitmap);
set_bit(BITOPS_7, g_bitmap);
set_bit(BITOPS_11, g_bitmap);
set_bit(BITOPS_31, g_bitmap);
set_bit(BITOPS_88, g_bitmap);
return 0;
}
static void __exit test_bitops_unstartup(void)
{
int bit_set;
clear_bit(BITOPS_4, g_bitmap);
clear_bit(BITOPS_7, g_bitmap);
clear_bit(BITOPS_11, g_bitmap);
clear_bit(BITOPS_31, g_bitmap);
clear_bit(BITOPS_88, g_bitmap);
bit_set = find_first_bit(g_bitmap, BITOPS_LAST);
if (bit_set != BITOPS_LAST)
pr_err("ERROR: FOUND SET BIT %d\n", bit_set);
pr_warn("Unloaded test module\n");
}
module_init(test_bitops_startup);
module_exit(test_bitops_unstartup);
MODULE_AUTHOR("Jesse Brandeburg <jesse.brandeburg@intel.com>");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Bit testing module");

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@ -2,3 +2,4 @@ CONFIG_TEST_PRINTF=m
CONFIG_TEST_BITMAP=m
CONFIG_PRIME_NUMBERS=m
CONFIG_TEST_STRSCPY=m
CONFIG_TEST_BITOPS=m