linux-kernel - Re: [PATCH v8 00/16] Add support for Clang LTO

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Date:   Wed, 9 Dec 2020 20:24:22 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.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 <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v8 00/16] Add support for Clang LTO

On Wed, Dec 9, 2020 at 5:09 PM 'Sami Tolvanen' via Clang Built Linux
<clang-built-linux@...glegroups.com> wrote:
> On Tue, Dec 8, 2020 at 1:02 PM Arnd Bergmann <arnd@...nel.org> wrote:
> > On Tue, Dec 8, 2020 at 9:59 PM Arnd Bergmann <arnd@...nel.org> wrote:
> > >
> > > Attaching the config for "ld.lld: error: Never resolved function from
> > >   blockaddress (Producer: 'LLVM12.0.0' Reader: 'LLVM 12.0.0')"
> >
> > And here is a new one: "ld.lld: error: assignment to symbol
> > init_pg_end does not converge"
>
> Thanks for these. I can reproduce the "Never resolved function from
> blockaddress" issue with full LTO, but I couldn't reproduce this one
> with ToT Clang, and the config doesn't have LTO enabled:
>
> $ grep LTO 0x2824F594_defconfig
> CONFIG_ARCH_SUPPORTS_LTO_CLANG_THIN=y
>
> Is this the correct config file?

It is the right file, and so far this is the only defconfig on which I
see the "does not converge" error, so I don't have any other one.

I suspect this might be an issue in the version of lld that I have here
and unrelated to LTO, and I can confirm that I see the error
with LTO still disabled.

It seems to be completely random. I do see the bug on next-20201203
but not on a later one. I also tried bisecting through linux-next and
arrived at "lib: stackdepot: add support to configure STACK_HASH_SIZE",
which is almost certainly not related, other than just changing a few
symbols around.

      Arnd