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Message-ID: <20200910150704.GA2041735@google.com>
Date: Thu, 10 Sep 2020 08:07:04 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: David Woodhouse <dwmw2@...radead.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Will Deacon <will@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Kees Cook <keescook@...omium.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
clang-built-linux@...glegroups.com,
kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
x86@...nel.org
Subject: Re: [PATCH v2 15/28] init: lto: ensure initcall ordering
On Thu, Sep 10, 2020 at 10:25:40AM +0100, David Woodhouse wrote:
> On Thu, 2020-09-03 at 13:30 -0700, Sami Tolvanen wrote:
> > With LTO, the compiler doesn't necessarily obey the link order for
> > initcalls, and initcall variables need globally unique names to avoid
> > collisions at link time.
> >
> > This change exports __KBUILD_MODNAME and adds the initcall_id() macro,
> > which uses it together with __COUNTER__ and __LINE__ to help ensure
> > these variables have unique names, and moves each variable to its own
> > section when LTO is enabled, so the correct order can be specified using
> > a linker script.
> >
> > The generate_initcall_ordering.pl script uses nm to find initcalls from
> > the object files passed to the linker, and generates a linker script
> > that specifies the intended order. With LTO, the script is called in
> > link-vmlinux.sh.
>
> Is this guaranteed to give you the *same* initcall ordering with LTO as
> without?
Yes. It follows the link order, just like the linker without LTO, and
also preserves the order within each file.
Sami
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