linux-kernel - Re: [PATCH 5/9] objtool: Rework rebuild

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Message-ID: <YFOIGYblhHTqp/fa@hirez.programming.kicks-ass.net>
Date:   Thu, 18 Mar 2021 18:04:25 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, jgross@...e.com, mbenes@...e.cz,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/9] objtool: Rework rebuild_reloc logic

On Thu, Mar 18, 2021 at 11:36:40AM -0500, Josh Poimboeuf wrote:
> > I was thinking you could get a section changed without touching
> > relocations, but while that is theoretically possible, it is exceedingly
> > unlikely (and objtool doesn't do that).
> 
> Hm?  This is a *relocation* section, not a normal one.  So by
> definition, it only changes when its relocations change.

The way I read this code:

 	list_for_each_entry(sec, &elf->sections, list) {
 		if (sec->changed) {
+			if (sec->reloc &&
+			    elf_rebuild_reloc_section(elf, sec->reloc)) {
+				WARN_ELF("elf_rebuild_reloc_section");
+				return -1;
+			}

is that we iterate the regular sections (which could be dirtied because
we changed some data), and if that section has a relocation section, we
rebuild that for good measure (even though it might not have altered
relocations).

Or am I just totally confused ?