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Traditionally, we have always had warnings about uninitialized variables enabled, as this is part of -Wall, and generally a good idea [1], but it also always produced false positives, mainly because this is a variation of the halting problem and provably impossible to get right in all cases [2]. Various people have identified cases that are particularly bad for false positives, and in commite74fc973b6("Turn off -Wmaybe-uninitialized when building with -Os"), I turned off the warning for any build that was done with CC_OPTIMIZE_FOR_SIZE. This drastically reduced the number of false positive warnings in the default build but unfortunately had the side effect of turning the warning off completely in 'allmodconfig' builds, which in turn led to a lot of warnings (both actual bugs, and remaining false positives) to go in unnoticed. With commit877417e6ff("Kbuild: change CC_OPTIMIZE_FOR_SIZE definition") enabled the warning again for allmodconfig builds in v4.7 and in v4.8-rc1, I had finally managed to address all warnings I get in an ARM allmodconfig build and most other maybe-uninitialized warnings for ARM randconfig builds. However, commit6e8d666e92("Disable "maybe-uninitialized" warning globally") was merged at the same time and disabled it completely for all configurations, because of false-positive warnings on x86 that I had not addressed until then. This caused a lot of actual bugs to get merged into mainline, and I sent several dozen patches for these during the v4.9 development cycle. Most of these are actual bugs, some are for correct code that is safe because it is only called under external constraints that make it impossible to run into the case that gcc sees, and in a few cases gcc is just stupid and finds something that can obviously never happen. I have now done a few thousand randconfig builds on x86 and collected all patches that I needed to address every single warning I got (I can provide the combined patch for the other warnings if anyone is interested), so I hope we can get the warning back and let people catch the actual bugs earlier. This reverts the change to disable the warning completely and for now brings it back at the "make W=1" level, so we can get it merged into mainline without introducing false positives. A follow-up patch enables it on all levels unless some configuration option turns it off because of false-positives. Link: https://rusty.ozlabs.org/?p=232 [1] Link: https://gcc.gnu.org/wiki/Better_Uninitialized_Warnings [2] Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
25 lines
1.0 KiB
Makefile
25 lines
1.0 KiB
Makefile
ifdef CONFIG_UBSAN
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=shift)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=integer-divide-by-zero)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=unreachable)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=vla-bound)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=signed-integer-overflow)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=object-size)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=returns-nonnull-attribute)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=bool)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=enum)
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ifdef CONFIG_UBSAN_ALIGNMENT
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=alignment)
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endif
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ifdef CONFIG_UBSAN_NULL
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=null)
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endif
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# -fsanitize=* options makes GCC less smart than usual and
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# increase number of 'maybe-uninitialized false-positives
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CFLAGS_UBSAN += $(call cc-option, -Wno-maybe-uninitialized)
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endif
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