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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2020-05-09 22:57:10 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-05-09 22:57:10 +0200 |
| commit | 78a5255ffb6a1af189a83e493d916ba1c54d8c75 (patch) | |
| tree | ff0c8ef475d1a5921fa761a96f01582a444fef0d | |
| parent | Merge tag 'io_uring-5.7-2020-05-08' of git://git.kernel.dk/linux-block (diff) | |
| download | linux-78a5255ffb6a1af189a83e493d916ba1c54d8c75.tar.xz linux-78a5255ffb6a1af189a83e493d916ba1c54d8c75.zip | |
Stop the ad-hoc games with -Wno-maybe-initialized
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 <torvalds@linux-foundation.org>
| -rw-r--r-- | Makefile | 7 | ||||
| -rw-r--r-- | init/Kconfig | 18 | ||||
| -rw-r--r-- | kernel/trace/Kconfig | 1 |
3 files changed, 3 insertions, 23 deletions
@@ -729,10 +729,6 @@ else ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += -Os endif -ifdef CONFIG_CC_DISABLE_WARN_MAYBE_UNINITIALIZED -KBUILD_CFLAGS += -Wno-maybe-uninitialized -endif - # Tell gcc to never replace conditional load with a non-conditional one KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0) KBUILD_CFLAGS += $(call cc-option,-fno-allow-store-data-races) @@ -881,6 +877,9 @@ KBUILD_CFLAGS += -Wno-pointer-sign # disable stringop warnings in gcc 8+ KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation) +# Enabled with W=2, disabled by default as noisy +KBUILD_CFLAGS += $(call cc-disable-warning, maybe-uninitialized) + # disable invalid "can't wrap" optimizations for signed / pointers KBUILD_CFLAGS += $(call cc-option,-fno-strict-overflow) diff --git a/init/Kconfig b/init/Kconfig index 9e22ee8fbd75..9278a603d399 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -39,22 +39,6 @@ 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 @@ -1257,14 +1241,12 @@ 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. diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 402eef84c859..743647005f64 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -466,7 +466,6 @@ config PROFILE_ANNOTATED_BRANCHES config PROFILE_ALL_BRANCHES bool "Profile all if conditionals" if !FORTIFY_SOURCE select TRACE_BRANCH_PROFILING - imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives help This tracer profiles all branch conditions. Every if () taken in the kernel is recorded whether it hit or miss. |