linux-kernel - Re: --orphan-handling=warn

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Date:   Tue, 25 Feb 2020 14:02:48 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Fangrui Song <maskray@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Michael Matz <matz@...e.de>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>
Subject: Re: --orphan-handling=warn

On Tue, Feb 25, 2020 at 12:37:26PM -0800, Nick Desaulniers wrote:
> On Tue, Feb 25, 2020 at 11:43 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Tue, Feb 25, 2020 at 01:29:51PM -0500, Arvind Sankar wrote:
> > > On Mon, Feb 24, 2020 at 09:35:04PM -0800, Kees Cook wrote:
> > > > Note that cheating and doing the 1-to-1 mapping by handy with a 40,000
> > > > entry linker script ... made ld.lld take about 15 minutes to do the
> > > > final link. :(
> > >
> > > Out of curiosity, how long does ld.bfd take on that linker script :)
> >
> > A single CPU at 100% for 15 minutes. :)
> 
> I can see the implementers of linker script handling thinking "surely
> no one would ever have >10k entries." Then we invented things like
> -ffunction-sections, -fdata-sections, (per basic block equivalents:
> https://reviews.llvm.org/D68049) and then finally FGKASLR. "640k ought
> to be enough for anybody" and such.

Heh, yeah. I had no expectation that it would work _well_; I just
wanted to test if it _could_ work. And it did: FGKASLR up and running
on Clang+LLD. I stopped there before attempting the next step:
FGKASLR+LTO+CFI, which I assume would be hilariously slow linking.

-- 
Kees Cook