linux-kernel - Re: [PATCH] kbuild: Merge module sections if and only if CONFIG_LTO

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Message-ID: <CABCJKudMQ9CP1zhvywTf-_=PY5zmeviURR+=PqsMn_bqa_MV-g@mail.gmail.com>
Date:   Tue, 23 Mar 2021 09:19:57 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] kbuild: Merge module sections if and only if
 CONFIG_LTO_CLANG is enabled

On Mon, Mar 22, 2021 at 4:44 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Merge module sections only when using Clang LTO.  With gcc-10, merging
> sections does not appear to update the symbol tables for the module,
> e.g. 'readelf -s' shows the value that a symbol would have had, if
> sections were not merged.

I'm fine with limiting this to LTO only, but it would be helpful to
understand which sections are actually getting merged here. Are you
compiling the kernel with -ffunction-sections and/or -fdata-sections?
Does this issue only happen with gcc 10?

Sami