linux-kernel - Re: [PATCH v6 14/25] kbuild: lto: remove duplicate dependencies from .mod files

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Date:   Thu, 3 Dec 2020 10:47:48 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.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-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        PCI <linux-pci@...r.kernel.org>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH v6 14/25] kbuild: lto: remove duplicate dependencies from
 .mod files

On Thu, Dec 3, 2020 at 10:00 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> On Thu, Oct 15, 2020 at 7:50 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Mon, Oct 12, 2020 at 05:31:52PM -0700, Sami Tolvanen wrote:
> > > With LTO, llvm-nm prints out symbols for each archive member
> > > separately, which results in a lot of duplicate dependencies in the
> > > .mod file when CONFIG_TRIM_UNUSED_SYMS is enabled. When a module
> > > consists of several compilation units, the output can exceed the
> > > default xargs command size limit and split the dependency list to
> > > multiple lines, which results in used symbols getting trimmed.
> > >
> > > This change removes duplicate dependencies, which will reduce the
> > > probability of this happening and makes .mod files smaller and
> > > easier to read.
> > >
> > > Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> > > Reviewed-by: Kees Cook <keescook@...omium.org>
> >
> > Hi Masahiro,
> >
> > This appears to be a general improvement as well. This looks like it can
> > land without depending on the rest of the series.
>
> It cannot.
> Adding "sort -u" is pointless without the rest of the series
> since the symbol duplication happens only with Clang LTO.
>
> This is not a solution.
> "reduce the probability of this happening" well describes it.
>
> I wrote a different patch.

Great, thanks for looking into this. I'll drop this patch from the next version.

Sami