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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>
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7
Makefile
7
Makefile
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@ -729,10 +729,6 @@ else ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
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KBUILD_CFLAGS += -Os
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endif
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ifdef CONFIG_CC_DISABLE_WARN_MAYBE_UNINITIALIZED
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KBUILD_CFLAGS += -Wno-maybe-uninitialized
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endif
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# Tell gcc to never replace conditional load with a non-conditional one
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KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0)
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KBUILD_CFLAGS += $(call cc-option,-fno-allow-store-data-races)
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@ -881,6 +877,9 @@ KBUILD_CFLAGS += -Wno-pointer-sign
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# disable stringop warnings in gcc 8+
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KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
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# Enabled with W=2, disabled by default as noisy
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KBUILD_CFLAGS += $(call cc-disable-warning, maybe-uninitialized)
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# disable invalid "can't wrap" optimizations for signed / pointers
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KBUILD_CFLAGS += $(call cc-option,-fno-strict-overflow)
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18
init/Kconfig
18
init/Kconfig
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@ -39,22 +39,6 @@ config TOOLS_SUPPORT_RELR
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config CC_HAS_ASM_INLINE
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def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
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config CC_HAS_WARN_MAYBE_UNINITIALIZED
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def_bool $(cc-option,-Wmaybe-uninitialized)
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help
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GCC >= 4.7 supports this option.
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config CC_DISABLE_WARN_MAYBE_UNINITIALIZED
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bool
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depends on CC_HAS_WARN_MAYBE_UNINITIALIZED
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default CC_IS_GCC && GCC_VERSION < 40900 # unreliable for GCC < 4.9
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help
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GCC's -Wmaybe-uninitialized is not reliable by definition.
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Lots of false positive warnings are produced in some cases.
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If this option is enabled, -Wno-maybe-uninitialzed is passed
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to the compiler to suppress maybe-uninitialized warnings.
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config CONSTRUCTORS
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bool
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depends on !UML
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@ -1257,14 +1241,12 @@ config CC_OPTIMIZE_FOR_PERFORMANCE
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config CC_OPTIMIZE_FOR_PERFORMANCE_O3
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bool "Optimize more for performance (-O3)"
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depends on ARC
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imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives
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help
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Choosing this option will pass "-O3" to your compiler to optimize
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the kernel yet more for performance.
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config CC_OPTIMIZE_FOR_SIZE
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bool "Optimize for size (-Os)"
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imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives
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help
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Choosing this option will pass "-Os" to your compiler resulting
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in a smaller kernel.
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@ -466,7 +466,6 @@ config PROFILE_ANNOTATED_BRANCHES
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config PROFILE_ALL_BRANCHES
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bool "Profile all if conditionals" if !FORTIFY_SOURCE
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select TRACE_BRANCH_PROFILING
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imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives
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help
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This tracer profiles all branch conditions. Every if ()
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taken in the kernel is recorded whether it hit or miss.
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