From: Mark Rutland <mark.rutland@arm.com>
To: Kees Cook <keescook@chromium.org>
Cc: linux-hardening@vger.kernel.org, Qing Zhao <qing.zhao@oracle.com>,
Masahiro Yamada <masahiroy@kernel.org>,
Michal Marek <michal.lkml@markovi.net>,
linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
linux-security-module@vger.kernel.org
Subject: Re: [PATCH] Makefile: Introduce CONFIG_ZERO_CALL_USED_REGS
Date: Tue, 11 May 2021 14:59:20 +0100 [thread overview]
Message-ID: <20210511135920.GB8933@C02TD0UTHF1T.local> (raw)
In-Reply-To: <202105101458.EC466299@keescook>
On Mon, May 10, 2021 at 03:01:48PM -0700, Kees Cook wrote:
> On Mon, May 10, 2021 at 02:45:03PM +0100, Mark Rutland wrote:
[...]
> > That's 441301 new MOVs, and the equivalent of 442511 new instructions
> > overall. There are 135728 new MOVs to x16 and x17 specifically, which
> > account for ~31% of that.
>
> I assume the x16/x17 case could be addressed by the compiler if it
> examined the need for PLTs, or is that too late (in the sense that the
> linker is doing that phase)?
Most (all?) PLTs will be created at link time, and IIUC the compiler
simply has to assume any non-static function might have a PLT, since the
AAPCS permits that. Maybe some of the smaller memory size models don't
permit PLTs, but I have no real knowledge of that area and I'm already
out on a limb.
LTO could probably help with visiblity, but otherwise I don't see a way
the compiler could be sure a PLT won't exist.
> Regardless, I will update the documentation on this feature. :)
Great; thanks!
Mark.
prev parent reply other threads:[~2021-05-11 13:59 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-05 19:18 [PATCH] Makefile: Introduce CONFIG_ZERO_CALL_USED_REGS Kees Cook
2021-05-06 12:54 ` Mark Rutland
2021-05-06 21:24 ` Kees Cook
2021-05-10 13:45 ` Mark Rutland
2021-05-10 22:01 ` Kees Cook
2021-05-11 13:59 ` Mark Rutland [this message]
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