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Stop the ad-hoc games with -Wno-maybe-initialized

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commit 78a5255ffb6a1af189a83e493d916ba1c54d8c75 upstream.

We have some rather random rules about when we accept the
"maybe-initialized" warnings, and when we don't.

For example, we consider it unreliable for gcc versions < 4.9, but also
if -O3 is enabled, or if optimizing for size.  And then various kernel
config options disabled it, because they know that they trigger that
warning by confusing gcc sufficiently (ie PROFILE_ALL_BRANCHES).

And now gcc-10 seems to be introducing a lot of those warnings too, so
it falls under the same heading as 4.9 did.

At the same time, we have a very straightforward way to _enable_ that
warning when wanted: use "W=2" to enable more warnings.

So stop playing these ad-hoc games, and just disable that warning by
default, with the known and straight-forward "if you want to work on the
extra compiler warnings, use W=123".

Would it be great to have code that is always so obvious that it never
confuses the compiler whether a variable is used initialized or not?
Yes, it would.  In a perfect world, the compilers would be smarter, and
our source code would be simpler.

That's currently not the world we live in, though.

Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Linus Torvalds 2020-05-09 13:57:10 -07:00 • committed by Greg Kroah-Hartman
commit 8f6a84167e
3 changed files with 3 additions and 23 deletions
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18
init/Kconfig
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@ -36,22 +36,6 @@ config TOOLS_SUPPORT_RELR
config CC_HAS_ASM_INLINE
def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
config CC_HAS_WARN_MAYBE_UNINITIALIZED
def_bool $(cc-option,-Wmaybe-uninitialized)
help
GCC >= 4.7 supports this option.
config CC_DISABLE_WARN_MAYBE_UNINITIALIZED
bool
depends on CC_HAS_WARN_MAYBE_UNINITIALIZED
default CC_IS_GCC && GCC_VERSION < 40900 # unreliable for GCC < 4.9
help
GCC's -Wmaybe-uninitialized is not reliable by definition.
Lots of false positive warnings are produced in some cases.
If this option is enabled, -Wno-maybe-uninitialzed is passed
to the compiler to suppress maybe-uninitialized warnings.
config CONSTRUCTORS
bool
depends on !UML
@ -1226,14 +1210,12 @@ config CC_OPTIMIZE_FOR_PERFORMANCE
config CC_OPTIMIZE_FOR_PERFORMANCE_O3
bool "Optimize more for performance (-O3)"
depends on ARC
imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives
help
Choosing this option will pass "-O3" to your compiler to optimize
the kernel yet more for performance.
config CC_OPTIMIZE_FOR_SIZE
bool "Optimize for size (-Os)"
imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives
help
Choosing this option will pass "-Os" to your compiler resulting
in a smaller kernel.