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authorLinus Torvalds <torvalds@linux-foundation.org>2020-05-09 13:57:10 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-05-20 08:20:28 +0200
commit8f6a84167e8618333d84ea4143812e3e74ced7da (patch)
tree890bfff3c62e74e6b159b234d2d6d33dab1f5305
parentab638a49a9f3ae4fcde0ca71b2a7eab87f71275b (diff)
Stop the ad-hoc games with -Wno-maybe-initialized
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 <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--Makefile7
-rw-r--r--init/Kconfig18
-rw-r--r--kernel/trace/Kconfig1
3 files changed, 3 insertions, 23 deletions
diff --git a/Makefile b/Makefile
index a8c772b299aa..2f423a010a87 100644
--- a/Makefile
+++ b/Makefile
@@ -707,10 +707,6 @@ 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)
@@ -860,6 +856,9 @@ 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 0bffc8fdbf3d..6db3e310a5e4 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -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.
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index e08527f50d2a..f3f2fc8ad81a 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -371,7 +371,6 @@ 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.