On Sat, 27 Jun 2020 at 17:44, Kees Cook <keesc...@chromium.org> wrote: > > On Thu, Jun 25, 2020 at 02:36:27AM +0800, kernel test robot wrote: > > I love your patch! Perhaps something to improve: > > [...] > > config: x86_64-randconfig-a012-20200624 (attached as .config) > > CONFIG_KCSAN=y > > > compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project > > 1d4c87335d5236ea1f35937e1014980ba961ae34) > > [...] > > All warnings (new ones prefixed by >>): > > > > ld.lld: warning: drivers/built-in.a(mfd/mt6397-irq.o):(.init_array.0) is > > being placed in '.init_array.0' > > As far as I can tell, this is a Clang bug. But I don't know the > internals here, so I've opened: > https://bugs.llvm.org/show_bug.cgi?id=46478 > > and created a work-around patch for the kernel:
Thanks, minor comments below. With KCSAN this is: Tested-by: Marco Elver <el...@google.com> > commit 915f2c343e59a14f00c68f4d7afcfdc621de0674 > Author: Kees Cook <keesc...@chromium.org> > Date: Sat Jun 27 08:07:54 2020 -0700 > > vmlinux.lds.h: Avoid KCSAN's unwanted sections Since you found that it's also KASAN, this probably wants updating. > KCSAN (-fsanitize=thread) produces unwanted[1] .eh_frame and .init_array.* > sections. Add them to DISCARDS, except with CONFIG_CONSTRUCTORS, which > wants to keep .init_array.* sections. > > [1] https://bugs.llvm.org/show_bug.cgi?id=46478 > > Signed-off-by: Kees Cook <keesc...@chromium.org> > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > index f8a5b2333729..41c8c73de6c4 100644 > --- a/arch/x86/Makefile > +++ b/arch/x86/Makefile > @@ -195,7 +195,9 @@ endif > # Workaround for a gcc prelease that unfortunately was shipped in a suse > release > KBUILD_CFLAGS += -Wno-sign-compare > # > -KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > +KBUILD_AFLAGS += -fno-asynchronous-unwind-tables -fno-unwind-tables > +KBUILD_CFLAGS += -fno-asynchronous-unwind-tables -fno-unwind-tables > +KBUILD_LDFLAGS += $(call ld-option,--no-ld-generated-unwind-info) Why are they needed? They are not mentioned in the commit message. > # Avoid indirect branches in kernel to deal with Spectre > ifdef CONFIG_RETPOLINE > diff --git a/include/asm-generic/vmlinux.lds.h > b/include/asm-generic/vmlinux.lds.h > index b1dca0762fc5..a44ee16abc78 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -934,10 +934,28 @@ > EXIT_DATA > #endif > > +/* > + * Clang's -fsanitize=thread produces unwanted sections (.eh_frame > + * and .init_array.*), but CONFIG_CONSTRUCTORS wants to keep any > + * .init_array.* sections. > + * https://bugs.llvm.org/show_bug.cgi?id=46478 > + */ > +#if defined(CONFIG_KCSAN) && !defined(CONFIG_CONSTRUCTORS) CONFIG_KASAN as well? > +#define KCSAN_DISCARDS \ > + *(.init_array) *(.init_array.*) \ > + *(.eh_frame) > +#elif defined(CONFIG_KCSAN) && defined(CONFIG_CONSTRUCTORS) > +#define KCSAN_DISCARDS \ > + *(.eh_frame) > +#else > +#define KCSAN_DISCARDS > +#endif > + > #define DISCARDS \ > /DISCARD/ : { \ > EXIT_DISCARDS \ > EXIT_CALL \ > + KCSAN_DISCARDS \ Maybe just 'SANITIZER_DISCARDS'? > *(.discard) \ > *(.discard.*) \ > *(.modinfo) \ > > -- > Kees Cook
