[+Masahiro] On Fri, Jan 10, 2020 at 06:35:02PM +0100, Arnd Bergmann wrote: > On Fri, Jan 10, 2020 at 5:56 PM Will Deacon <will@xxxxxxxxxx> wrote: > > > > 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. > > No objection to recommending gcc-4.8, but I think this should either > just warn once during the kernel build instead of for every file, or > it should become a hard requirement. Oops, yes, good point. I blindly followed the '< 4.6' check, but that's actually a '#error' so it doesn't have the issue you mention. I've had a crack at moving the check into kbuild -- see below. Will --->8 diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 62afe874073e..d7ee4c6bad48 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -14,10 +14,6 @@ # error Sorry, your compiler is too old - please upgrade it. #endif -#if GCC_VERSION < 40800 -# warning Your compiler is old and may miscompile the kernel due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 - please upgrade it. -#endif - /* Optimization barrier */ /* The "volatile" is due to gcc bugs */ diff --git a/init/Kconfig b/init/Kconfig index a34064a031a5..bdc2f1b1667b 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -10,11 +10,11 @@ config DEFCONFIG_LIST default "arch/$(ARCH)/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 CC_IS_CLANG diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include index d4adfbe42690..4e645a798b56 100644 --- a/scripts/Kconfig.include +++ b/scripts/Kconfig.include @@ -40,3 +40,9 @@ $(error-if,$(success, $(LD) -v | grep -q gold), gold linker '$(LD)' not supporte # 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.")
