From: Linus Torvalds <torva...@linux-foundation.org>
[ Upstream commit 78a5255ffb6a1af189a83e493d916ba1c54d8c75 ]
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 <torva...@linux-foundation.org>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
Makefile | 7 +++----
init/Kconfig | 18 ------------------
kernel/trace/Kconfig | 1 -
3 files changed, 3 insertions(+), 23 deletions(-)
diff --git a/Makefile b/Makefile
index 744245f0c96cf..d226ec8bd167f 100644
--- a/Makefile
+++ b/Makefile
@@ -708,10 +708,6 @@ 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)
@@ -862,6 +858,9 @@ 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 4f717bfdbfe2d..ef59c5c36cdb5 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
@@ -1249,14 +1233,12 @@ 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 402eef84c859a..743647005f64e 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.
--
2.20.1
