linux-kernel - Re: [PATCH] fix compilation of 64-bit kernel with 32-bit compiler

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Message-ID: <20180308151754.d7wozkcuapi4bpvn@treble>
Date:   Thu, 8 Mar 2018 09:17:54 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mikulas Patocka <mpatocka@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix compilation of 64-bit kernel with 32-bit compiler

On Thu, Mar 08, 2018 at 10:39:44AM +0100, Peter Zijlstra wrote:
> On Thu, Mar 08, 2018 at 04:09:30AM -0500, Mikulas Patocka wrote:
> > 
> > 
> > On Thu, 8 Mar 2018, Peter Zijlstra wrote:
> > 
> > > On Thu, Mar 08, 2018 at 01:11:26AM -0500, Mikulas Patocka wrote:
> > > > The patch b5bc2231b8ad4387c9641f235ca0ad8cd300b6df ("objtool: Add 
> > > > retpoline validation") broke compiling 64-bit kernel with 32-bit compiler.
> > > > 
> > > > This patch fixes the following error and a large number of "can't find
> > > > rela for retpoline_safe" errors that occur when using x32 or i386 gcc.
> > > > 
> > > > You shouldn't use the type 'unsigned long' in objtool at all - because its
> > > > size depends on the compiler and not on the kernel you are compiling.
> > > 
> > > Your patch is wrong because the data field is actually a long. A correct
> > > patch is already in merged in tip.
> > 
> > I'm wondering, why is objtool using 'unsigned long' at all? Why not 
> > uint32_t and uint64_t? The size of 'unsigned long' is dependent on the 
> > compiler, so it will lead to different behavior.
> 
> Because pointers... As Josh said, I should've used the right ELF methods
> which use the object's ABI.

But there are still a few other places where objtool uses longs
unnecessarily.  Those should probably be converted.  Patches welcome...

-- 
Josh