On Thu, Apr 16, 2020 at 1:52 AM 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. This patch is unneeded since you will remove GCC 4.8 support in 11/12. Please move 11/12 to the head of this series, and remove all noise changes. Thanks. > 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 > -- Best Regards Masahiro Yamada
