linux-kernel - [PATCH v2] KVM: arm64: nvhe: Fix build with profile optimization

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Message-Id: <20220922053145.944786-1-denik@chromium.org>
Date:   Wed, 21 Sep 2022 22:31:45 -0700
From:   Denis Nikitin <denik@...omium.org>
To:     Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Manoj Gupta <manojgupta@...gle.com>,
        David Brazdil <dbrazdil@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, Denis Nikitin <denik@...omium.org>
Subject: [PATCH v2] KVM: arm64: nvhe: Fix build with profile optimization

Kernel build with clang and KCFLAGS=-fprofile-sample-use 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.

Remove ".llvm.call-graph-profile" SHT_REL relocation from kvm_nvhe
to fix the build.

Signed-off-by: Denis Nikitin <denik@...omium.org>
---
V1 -> V2: Remove the relocation instead of disabling the profile-use flags.
---
 arch/arm64/kvm/hyp/nvhe/Makefile | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
index b5c5119c7396..49ec950ac57b 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -78,8 +78,10 @@ $(obj)/kvm_nvhe.o: $(obj)/kvm_nvhe.rel.o FORCE
 
 # The HYPREL command calls `gen-hyprel` to generate an assembly file with
 # a list of relocations targeting hyp code/data.
+# 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.
 quiet_cmd_hyprel = HYPREL  $@
-      cmd_hyprel = $(obj)/gen-hyprel $< > $@
+	cmd_hyprel = $(OBJCOPY) -R .llvm.call-graph-profile $<; $(obj)/gen-hyprel $< > $@
 
 # The HYPCOPY command uses `objcopy` to prefix all ELF symbol names
 # to avoid clashes with VHE code/data.
-- 
2.37.3.968.ga6b4b080e4-goog