linux-kernel - Re: [PATCH 01/13] objtool: Rewrite hashtable sizing

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Date:   Thu, 10 Jun 2021 11:50:36 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH 01/13] objtool: Rewrite hashtable sizing

On Thu, Jun 10, 2021 at 11:14 AM Nathan Chancellor <nathan@...nel.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

Sami