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SubjectRe: [PATCH] KVM: arm64: Disable LTO in hyp
On Thu, 04 Mar 2021 18:45:44 +0000,
Sami Tolvanen <samitolvanen@google.com> wrote:
>
> allmodconfig + CONFIG_LTO_CLANG_THIN=y fails to build due to following
> linker errors:
>
> ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21CC):

I assume this message is only an oddity, right? Because
__guest_enter() is as far as you can imagine from irqbypass.c...

> 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.

Can you shed some light on what the problem is exactly?

>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1317
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Tested-by: Nathan Chancellor <nathan@kernel.org>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.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

Can this be reduced to the nvhe part of the tree? The rest of the
hypervisor should support being built with LTO, I'd expect. Or am I
missing something more significant?

Thanks,

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

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