2022-10-14 19:14:06

by Denis Nikitin

Subject: [PATCH v3] KVM: arm64: nvhe: Fix build with profile optimization

Kernel build with clang and KCFLAGS=-fprofile-sample-use=<profile> fails with:

error: arch/arm64/kvm/hyp/nvhe/kvm_nvhe.tmp.o: Unexpected SHT_REL
section ".rel.llvm.call-graph-profile"

Starting from 13.0.0 llvm can generate SHT_REL section, see
https://reviews.llvm.org/rGca3bdb57fa1ac98b711a735de048c12b5fdd8086.
gen-hyprel does not support SHT_REL relocation section.

Filter out profile use flags to fix the build with profile optimization.

Signed-off-by: Denis Nikitin <[email protected]>
---
V2 -> V3: Filter out the profile-use flags.
V1 -> V2: Remove the relocation instead of disabling the profile-use flags.
---
arch/arm64/kvm/hyp/nvhe/Makefile | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
index b5c5119c7396..16c6abdda494 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -89,6 +89,10 @@ 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))
+# Starting from 13.0.0 llvm emits SHT_REL section '.llvm.call-graph-profile'
+# when profile optimization is applied. gen-hyprel does not support SHT_REL and
+# causes a build failure. Remove profile optimization flags.
+KBUILD_CFLAGS := $(filter-out -fprofile-sample-use=% -fprofile-use=%, $(KBUILD_CFLAGS))

# KVM nVHE code is run at a different exception code with a different map, so
# compiler instrumentation that inserts callbacks or checks into the code may
--
2.38.0.413.g74048e4d9e-goog

2022-10-15 15:12:20

by Marc Zyngier

Subject: Re: [PATCH v3] KVM: arm64: nvhe: Fix build with profile optimization

On Fri, 14 Oct 2022 11:45:32 -0700, Denis Nikitin wrote:
> Kernel build with clang and KCFLAGS=-fprofile-sample-use=<profile> fails with:
>
> error: arch/arm64/kvm/hyp/nvhe/kvm_nvhe.tmp.o: Unexpected SHT_REL
> section ".rel.llvm.call-graph-profile"
>
> Starting from 13.0.0 llvm can generate SHT_REL section, see
> https://reviews.llvm.org/rGca3bdb57fa1ac98b711a735de048c12b5fdd8086.
> gen-hyprel does not support SHT_REL relocation section.
>
> [...]

Applied to fixes, thanks!

[1/1] KVM: arm64: nvhe: Fix build with profile optimization
commit: bde971a83bbff78561458ded236605a365411b87

Cheers,

M.
--
Without deviation from the norm, progress is not possible.