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lib: make a test module with set/clear bit

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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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13
lib/Kconfig.debug
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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