Prior to version 4.8, GCC may miscompile READ_ONCE() by erroneously discarding the 'volatile' qualifier: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 We've been working around this using some nasty hacks which make READ_ONCE() both horribly complicated and also prevent us from enforcing that it is only used on scalar types. Since GCC 4.8 is pretty old for kernel builds now, emit a warning if we detect it during the build. Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx> Signed-off-by: Will Deacon <will@xxxxxxxxxx> --- init/Kconfig | 4 ++-- scripts/Kconfig.include | 9 +++++++++ 2 files changed, 11 insertions(+), 2 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 9e22ee8fbd75..816b8b4a5e9e 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -9,11 +9,11 @@ config DEFCONFIG_LIST default "arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)" config CC_IS_GCC - def_bool $(success,$(CC) --version | head -n 1 | grep -q gcc) + def_bool $(cc-is-gcc) config GCC_VERSION int - default $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) if CC_IS_GCC + default $(gcc-version) if CC_IS_GCC default 0 config LD_VERSION diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include index c264da2b9b30..5261e9d6b50b 100644 --- a/scripts/Kconfig.include +++ b/scripts/Kconfig.include @@ -54,3 +54,12 @@ $(error-if,$(success, $(LD) -v | grep -q gold), gold linker '$(LD)' not supporte cc-option-bit = $(if-success,$(CC) -Werror $(1) -E -x c /dev/null -o /dev/null,$(1)) m32-flag := $(cc-option-bit,-m32) m64-flag := $(cc-option-bit,-m64) + +# gcc version including patch level +gcc-version := $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) + +# Return y if the compiler is GCC, n otherwise +cc-is-gcc := $(success,$(CC) --version | head -n 1 | grep -q gcc) + +# Warn if the compiler is GCC prior to 4.8 +$(warning-if,$(if-success,[ $(gcc-version) -lt 40800 ],$(cc-is-gcc),n),"Your compiler is old and may miscompile the kernel due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 - please upgrade it.") -- 2.26.0.110.g2183baf09c-goog
