linux-kernel - [PATCH 5.15.y] KVM: arm64: nvhe: Fix build with profile optimization

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Date:   Thu, 12 Jan 2023 16:22:10 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     stable@...r.kernel.org
Cc:     Denis Nikitin <denik@...omium.org>, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev, Marc Zyngier <maz@...nel.org>
Subject: [PATCH 5.15.y] KVM: arm64: nvhe: Fix build with profile optimization

From: Denis Nikitin <denik@...omium.org>

commit bde971a83bbff78561458ded236605a365411b87 upstream.

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 <denik@...omium.org>
Signed-off-by: Marc Zyngier <maz@...nel.org>
Link: https://lore.kernel.org/r/20221014184532.3153551-1-denik@chromium.org
Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---

I need this to properly compile 5.15.y stable kernels in the chromeos build
system.

 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 8d741f71377f..964c2134ea1e 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -83,6 +83,10 @@ 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
-- 
https://chromeos.dev