linux-hardening - Re: [PATCH] kbuild: merge module sections under CONFIG_LD_DEAD_CODE_DATA

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Date:   Fri, 2 Apr 2021 08:09:00 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Alexander Lobakin <alobakin@...me>
Cc:     Kees Cook <keescook@...omium.org>, Jessica Yu <jeyu@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-hardening@...r.kernel.org,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: merge module sections under CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
 too

On Fri, Apr 2, 2021 at 5:40 AM Alexander Lobakin <alobakin@...me> wrote:
>
> When building with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION,
> -fdata-sections and -ffunction-sections are being enabled by the
> top-level Makefile, and module section merging is also needed.
> Expand the ifdef (and the comment block) to cover that case too.
>
> Fixes: 6a3193cdd5e5 ("kbuild: lto: Merge module sections if and only if CONFIG_LTO_CLANG is enabled")

Wouldn't this trigger the ld.bfd bug described in the commit message
when LD_DEAD_CODE_DATA_ELIMINATION is enabled? LTO_CLANG always uses
LLD, so it won't have this issue.

Sami