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From:   Sami Tolvanen <samitolvanen@google.com>
Date:   Thu, 10 Jun 2021 12:43:56 -0700
Message-ID: <CABCJKudpajMRFGpn4Vh-JWzyfprEVrtYzX79iwp++rPu6rQWHw@mail.gmail.com>
Subject: Re: [PATCH 01/13] objtool: Rewrite hashtable sizing
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Nathan Chancellor <nathan@kernel.org>, X86 ML <x86@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Jason Baron <jbaron@akamai.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Thu, Jun 10, 2021 at 12:33 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Thu, Jun 10, 2021 at 11:50:36AM -0700, Sami Tolvanen wrote:
> > On Thu, Jun 10, 2021 at 11:14 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > > Adding Sami because I am not sure why this patch would have much of an impact
> > > in relation to LTO. https://git.kernel.org/tip/25cf0d8aa2a3 is the patch in
> > > question.
> >
> > It's because LLVM enables -ffunction-sections with LTO, so using .text
> > section size to estimate the reloc hash table size isn't going to be
> > accurate, as confirmed by objtool output with --stats:
> >
> >   OBJTOOL vmlinux.o
> > nr_sections: 141481
> > section_bits: 17
> > nr_symbols: 215262
> > symbol_bits: 17
> > max_reloc: 24850
> > tot_reloc: 590890
> > reloc_bits: 10
>
> Bah. Would something like the *completely* untested below help with that?

Yes, that seems to work:

tot_reloc: 590890
reloc_bits: 19

Nathan, can you confirm if this fixes the regression for you?

Sami