On Tue, Oct 17, 2017 at 12:38:14PM +0100, Will Deacon wrote: > On Tue, Oct 17, 2017 at 12:10:33PM +0100, Mark Rutland wrote: > > On Tue, Oct 17, 2017 at 11:58:58AM +0100, Will Deacon wrote: > > > On Tue, Oct 17, 2017 at 11:54:54AM +0100, Mark Rutland wrote: > > > > On Tue, Oct 17, 2017 at 11:03:15AM +0100, Will Deacon wrote: > > > > > On Mon, Oct 16, 2017 at 02:24:38PM +0100, Mark Rutland wrote: > > > > > > While we build the LL/SC atomics as a C object file, this does not > > > > > > follow the AAPCS. This does not interoperate with other C code, and can > > > > > > only be called from special wrapper assembly. > > > > > > > > > > > > Bulding a kernel with CONFIG_KCOV and CONFIG_ARM64_LSE_ATOMICS results > > > > > > in the cmopiler inserting calls to __sanitizer_cov_trace_pc within the > > > > > > LL/SC atomics. As __sanitizer_cov_trace_pc is built per the AAPCS, these > > > > > > calls corrupt register values, resulting in failures at boot time. > > > > > > > > > > > > Avoid this (and other similar issues) by opting out of all compiler > > > > > > instrumentation. We can opt-in to specific instrumentation in future if > > > > > > we want to. > > > > > > > > diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile > > > > > > index a0abc142c92b..af77516f71b2 100644 > > > > > > --- a/arch/arm64/lib/Makefile > > > > > > +++ b/arch/arm64/lib/Makefile > > > > > > @@ -17,5 +17,6 @@ CFLAGS_atomic_ll_sc.o := -fcall-used-x0 -ffixed-x1 -ffixed-x2 \ > > > > > > -fcall-saved-x10 -fcall-saved-x11 -fcall-saved-x12 \ > > > > > > -fcall-saved-x13 -fcall-saved-x14 -fcall-saved-x15 \ > > > > > > -fcall-saved-x18 > > > > > > +CC_INSTRUMENT_atomic_ll_sc.o := n > > > > > > > > > > Does this mean we can lose the "notrace" definition of __LL_SC_INLINE > > > > > when generating the out-of-line atomics? > > > > > > > > Unfortunately not. > > > > > > > > I'd missed -pg, since that isn't handled in scripts/Makefile.lib, and > > > > doesn't seem to have a makefile-level disable. > > > > > > > > I'll see if that can be remedied. > > > > > > Thanks. It's a real shame to have a "just use this option to avoid > > > instrumentation" if it doesn't actually catch everything. > > > > Agreed; it defeats the purpose of the exercise. > > > > > We probably need to think about kprobes too, but not really sure what > > > you can do there on a per-file basis. > > > > Ugh; that's a much more painful one, yes. :( > > > > Does that rely on any compiler options at all? I thought was all a > > runtime thing. > > > > Arguably it is somewhat separate for compiler instrumentation, and it > > might make sense for that to be a separate option. > > Yes, I suppose the problem here is that opting out of dynamic tracing > requires function attributes such as notrace and __kprobes, rather than a > compiler flag. If there's no way to say to the compiler "act as though > every function in this compilation unit is tagged with this attribute" then > we probably can't do anything to solve this easily. Unfortunately, I'm not aware of any way to do that short of using a linker script to rewrite sections. > We should probably add __kprobes to __LL_SC_INLINE though. Agreed. It's a different case, but kprobes can use atomics behind the scenes (e.g. via aarch64_insn_patch_text_cb()), and so those need to be blacklisted. I'll add a patch to this series, unless you plan to put one together. Thanks, Mark. -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
