Adding a few more comments... On Tue, Sep 20, 2022 at 5:08 PM Denis Nikitin <denik@xxxxxxxxxx> wrote: > > Hi Mark, > > Thank you for a quick response. > > On Tue, Sep 20, 2022 at 2:34 AM Marc Zyngier <maz@xxxxxxxxxx> wrote: > > > > Hi Denis, > > > > On Tue, 20 Sep 2022 09:20:05 +0100, > > Denis Nikitin <denik@xxxxxxxxxxxx> wrote: > > > > > > Kernel build with -fprofile-sample-use raises the following failure: > > > > > > error: arch/arm64/kvm/hyp/nvhe/kvm_nvhe.tmp.o: Unexpected SHT_REL > > > section ".rel.llvm.call-graph-profile" > > > > How is this flag provided? I don't see any occurrence of it in the > > kernel so far. > > On ChromeOS we build the kernel with sample profiles by adding > -fprofile-sample-use=/path/to/gcov.profile to KCFLAGS. > > > > > > > > > SHT_REL is generated by the latest lld, see > > > https://reviews.llvm.org/rGca3bdb57fa1ac98b711a735de048c12b5fdd8086. > > > > Is this part of a released toolchain? If so, can you spell out the > > first version where this occurs? > > Yes, it was added in llvm-13. I will update the patch. > > > > > > Disable profile optimization in kvm/nvhe to fix the build with > > > AutoFDO. > > > > It'd be good to at least mention how AutoFDO and -fprofile-sample-use > > relate to each other. > > Good point. AutoFDO is an example of sample profiles. > It's not actually relevant for the bug. I will better remove it. > > > > > > > > > Signed-off-by: Denis Nikitin <denik@xxxxxxxxxxxx> > > > --- > > > arch/arm64/kvm/hyp/nvhe/Makefile | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile > > > index b5c5119c7396..6a6188374a52 100644 > > > --- a/arch/arm64/kvm/hyp/nvhe/Makefile > > > +++ b/arch/arm64/kvm/hyp/nvhe/Makefile > > > @@ -89,6 +89,9 @@ quiet_cmd_hypcopy = HYPCOPY $@ > > > # Remove ftrace, Shadow Call Stack, and CFI CFLAGS. > > > # This is equivalent to the 'notrace', '__noscs', and '__nocfi' annotations. > > > KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS) $(CC_FLAGS_CFI), $(KBUILD_CFLAGS)) > > > +# Profile optimization creates SHT_REL section '.llvm.call-graph-profile' for > > > +# the hot code. SHT_REL is currently not supported by the KVM tools. > > > > 'KVM tools' seems vague. Maybe call out the actual helper that > > processes the relocations? > > Agreed. > > > > > > +KBUILD_CFLAGS += $(call cc-option,-fno-profile-sample-use,-fno-profile-use) > > > > Why adding these options instead of filtering out the offending option > > as it is done just above? > > That was actually the alternative solution and it worked as well. > Let me double check if profile optimization doesn't mess up with other > sections and if it doesn't I will remove the '.llvm.call-graph-profile' > section instead. When I remove the '.llvm.call-graph-profile' section the layout of other sections slightly changes (offsets and sizes) compared to `-fno-profile-sample-use`. But the list of sections remains the same. > > > > > Also, is this the only place the kernel fails to compile? The EFI stub > > does similar things AFAIR, and could potentially fail the same way. > > This was the only place in 5.15 where we tested it. > Let me see if EFI has this section. EFI code is not marked as hot in the profile. Regarding "could potentially fail", I don't see any explicit manipulations with code sections in EFI. The hardcoded EFI stub entries should not be affected. > > > > > Thanks, > > > > M. > > > > -- > > Without deviation from the norm, progress is not possible. > > Thanks, > Denis - Denis _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
