linux-kernel - Bug: MODPOST mismatch ignored due to LTO

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Date:   Thu, 24 Nov 2022 12:31:31 +0000
From:   Vincent Donnefort <vdonnefort@...gle.com>
To:     llvm@...ts.linux.dev, linux-kernel@...r.kernel.org
Cc:     samitolvanen@...gle.com, nhuck@...gle.com, ndesaulniers@...gle.com,
        kernel-team@...roid.com
Subject: Bug: MODPOST mismatch ignored due to LTO

Hi all,

It seems that enabling LTO breaks the check for section mismatch in modpost.

If I create on purpose a mismatch here's the output without LTO

check_section_mismatch()
  fromsec=.text
  tosec=.init.text
  sym=kvm_arch_vcpu_create

=> section mismatch in reference: kvm_vm_ioctl_create_vcpu (section: .text) -> kvm_arch_vcpu_create (section: .init.text)

While with LTO:

check_section_mismatch()
  fromsec=.text.kvm_vm_ioctl_create_vcpu 
  tosec=.init.text
  sym=kvm_arch_vcpu_create

=> mismatch ignored, the section ".text.kvm_vm_ioctl_create_vcpu" is
unsurprisingly unknown

LTO seems to append the symbol name to the section which is a problem for
modpost.

Is that a known issue?

Thanks,
Vincent