linux-kernel - Re: [PATCH 00/10] objtool: Honey, I shrunk the instruction^Wreloc

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Message-ID: <Y+ZLA/m5sp7aU+Qo@hirez.programming.kicks-ass.net>
Date:   Fri, 10 Feb 2023 14:47:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     x86@...nel.org, jpoimboe@...hat.com, linux@...ssschuh.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/10] objtool: Honey, I shrunk the instruction^Wreloc

On Fri, Feb 10, 2023 at 09:59:05AM +0100, Peter Zijlstra wrote:
> On Thu, Feb 09, 2023 at 11:57:40AM -0800, Josh Poimboeuf wrote:
> 
> > To make the last patch legit we could just have reloc_offset(),
> > reloc_addend(), reloc_type() helpers to abstract access to rela/rel
> > fields.
> > 
> > And I'm sure there are other savings we could do to struct reloc, like
> > single-linked lists, bitfields, etc.
> > 
> > Let me know if you want me to do it.
> 
> I'll make a start today -- I've got snot pouring out of me, so thinking
> isn't going to happen, might as well just do the busy work :-)

(lightly tested...)

Shrinks reloc from 120 to 80 bytes:

  https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=objtool/shrink-reloc

pre:	5:03.34 real,   210.75 user,    88.80 sys,      20241232 mem
post:	4:12.71 real,   188.21 user,    64.49 sys,      18144848 mem

(still running on the exact same allyesconfig image)

I can probably get rid of symbol::reloc_list if I rewrite that whole
symtable trainwreck and I think I can also get rid of
instruction::alt_group, but both of those are a bit more work.