linux-kernel - Re: [RFC][PATCH 4/5] objtool: Enable compilation of objtool for all architectures

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Message-ID: <20200519174817.GR9040@rlwimi.vmware.com>
Date:   Tue, 19 May 2020 10:48:17 -0700
From:   Matt Helsley <mhelsley@...are.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
CC:     <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Julien Thierry <jthierry@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC][PATCH 4/5] objtool: Enable compilation of objtool for all
 architectures

On Mon, May 18, 2020 at 05:27:54PM -0500, Josh Poimboeuf wrote:
> On Mon, May 18, 2020 at 12:50:45PM -0700, Matt Helsley wrote:
> > > Why were these moved to arch.h?  They're not necessarily arch-specific,
> > > but rather "check"-specific, so I think they still belong in check.h, if
> > > possible.
> > 
> > Ah, found it. They are arch specific due to struct orc_entry, which is
> > presently not defined for any archs besides x86.
> > 
> > Prior to the patch (-> means "includes"):
> > 	check.h -> asm/orc_types.h (defines struct orc_entry)
> > 	orc_gen.c -> check,h
> > 
> > After patch:
> > 	check.c -> asm/orc_types.h
> > 	orc_gen.c -> asm/orc_types.h
> > 	orc_gen.c -> check.h
> > 	orc_gen.c -> arch.h
> > 	{ now weak.c } -> check.h
> > 
> > So this prevents the headers, which help us keep the weak definitions
> > consistent with the strong definitions, from breaking compiles on archs
> > that lack struct orc_entry.
> > 
> > I'm not sure what the best way to remove this dependency is without
> > a nasty void * for the orc entry, or some #ifdef games related to
> > checking for cpp defines from asm/orc_types.h. This approach neatly
> > avoids conditional preprocessor games and type casting though I do
> > agree it's surprising.
> > 
> > Do you have any advice here?
> 
> Would it work if we just move the check() and orc_dump() prototypes to
> objtool.h?  Then weak.c can just include objtool.h.  And check.h and
> orc.h would only need to be included for arches which implement them.

OK, I tested that and it works well. In fact it simplifies the includes
a bit so I think it might be the right move.

Cheers,
	-Matt Helsley