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From: Alexander Lobakin <alobakin@pm.me>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: Kees Cook <keescook@chromium.org>, Jessica Yu <jeyu@kernel.org>,
	Miroslav Benes <mbenes@suse.cz>,
	Emil Velikov <emil.l.velikov@gmail.com>,
	Sean Christopherson <seanjc@google.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	"linux-hardening@vger.kernel.org"
	<linux-hardening@vger.kernel.org>,
	linux-kbuild <linux-kbuild@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kbuild: merge module sections under CONFIG_LD_DEAD_CODE_DATA_ELIMINATION too
Date: Tue, 06 Apr 2021 14:42:27 +0000	[thread overview]
Message-ID: <Gt4--xIFQdFQbd97OwKvRwelvfikSSv3Vkc_KKzAeGgp6c2fe8SPW6v_njp0xvwepPwC_UcWdyWeAjSdFEXpheJWlnmWNY-mVsaMEnJV56A=@pm.me> (raw)
In-Reply-To: <CABCJKufH262ki4FCQJxSO-v+gQzPBsVntQWnNZY7h-cvt1KYTA@mail.gmail.com>

On Friday, 2 April 2021, 18:09, Sami
Tolvanen <samitolvanen@google.com> wrote:

> On Fri, Apr 2, 2021 at 5:40 AM Alexander Lobakin alobakin@pm.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.

LD_DEAD_CODE_DATA_ELIMINATION is marked
“EXPERIMENTAL“ in the config prompt, and
arches have to opt-in
HAS_LD_DEAD_CODE_DATA_ELIMINATION to give
an access to it (only a few does). This
should be relatively safe.

> Sami

Thanks,
Al

  reply	other threads:[~2021-04-06 14:42 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-02 12:40 [PATCH] kbuild: merge module sections under CONFIG_LD_DEAD_CODE_DATA_ELIMINATION too Alexander Lobakin
2021-04-02 15:09 ` Sami Tolvanen
2021-04-06 14:42   ` Alexander Lobakin [this message]
2021-04-07 14:24     ` Masahiro Yamada

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