summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2020-05-09 13:57:10 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-05-09 13:57:10 -0700
commit78a5255ffb6a1af189a83e493d916ba1c54d8c75 (patch)
treeff0c8ef475d1a5921fa761a96f01582a444fef0d
parent1d3962ae3b3d3a945f7fd5c651cf170a27521a35 (diff)
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--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 3512f7b243dc..1e94f4f15d92 100644
--- a/Makefile
+++ b/Makefile
@@ -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.