linux-kernel - [PATCH] KVM: arm64: Disable LTO in hyp

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Message-Id: <20210304184544.2014171-1-samitolvanen@google.com>
Date:   Thu,  4 Mar 2021 10:45:44 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH] KVM: arm64: Disable LTO in hyp

allmodconfig + CONFIG_LTO_CLANG_THIN=y fails to build due to following
linker errors:

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21CC):
  relocation R_AARCH64_CONDBR19 out of range: 2031220 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21E0):
  relocation R_AARCH64_ADR_PREL_LO21 out of range: 2031200 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

As LTO is not really necessary for the hypervisor code, disable it for
the hyp directory to fix the build.

Link: https://github.com/ClangBuiltLinux/linux/issues/1317
Reported-by: Nathan Chancellor <nathan@...nel.org>
Tested-by: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 arch/arm64/kvm/hyp/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
index 687598e41b21..e8116016e6a8 100644
--- a/arch/arm64/kvm/hyp/Makefile
+++ b/arch/arm64/kvm/hyp/Makefile
@@ -11,3 +11,6 @@ subdir-ccflags-y := -I$(incdir)				\
 		    $(DISABLE_STACKLEAK_PLUGIN)
 
 obj-$(CONFIG_KVM) += vhe/ nvhe/ pgtable.o
+
+# Disable LTO for the files in this directory
+KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS))

base-commit: f69d02e37a85645aa90d18cacfff36dba370f797
-- 
2.30.1.766.gb4fecdf3b7-goog