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/[email protected]
Signed-off-by: Jesse Brandeburg <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Cc: Thomas Gleixner <[email protected]>
CcL Ingo Molnar <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Wei Yang <[email protected]>
Cc: Christian Brauner <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions