linux-kernel - Re: [PATCH v4 2/2] x86/purgatory: Make sure we fail the build if purgatory.ro has missing symbols

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Date:   Thu, 12 Mar 2020 14:23:23 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] x86/purgatory: Make sure we fail the build if
 purgatory.ro has missing symbols

On Thu, Mar 12, 2020 at 06:46:44PM +0100, Hans de Goede wrote:
> Hi,
> 
> On 3/12/20 1:10 AM, Arvind Sankar wrote:
> > On Wed, Mar 11, 2020 at 10:46:01PM +0100, Hans de Goede wrote:
> >> Since we link purgatory.ro with -r aka we enable "incremental linking"
> >> no checks for unresolved symbols is done while linking purgatory.ro.
> >>
> > 
> > Do we actually need to link purgatory with -r? We could use
> > --emit-relocs to get the relocation sections generated the way the main
> > x86 kernel does, no?
> > 
> > Eg like the below? This would avoid the double-link creating
> > purgatory.chk.
> 
> So I've changed the patch for this in my local tree over to the version
> suggested below and tested kexec with this (and I can confirm that it
> still works)
> 
> I'm wondering though if it would not be better to keep the purgatory.ro name ?  :
> 
> 1. The generated ELF binary should still be relocatable
> 2. .ro files are part of the global .gitignore settings, for the
>     new purgatory name we need to add an arch/x86/purgatory/.gitignore file
> 3. Keeping the purgatory.ro name will make the diff easier to read
> 
> Regards,
> 
> Hans
> 

No objections to the name, we can change it later to purgatory.elf or
something if we want in a separate patch.

There is one issue I noticed -- x86_64 kernel default LDFLAGS have
max-page-size=0x200000. If purgatory is linked into a real executable
this makes kexec-purgatory.o become quite large, from about 25k to just
over 4Mb.  Adding -z max-page-size=4096 to the LDFLAGS lowers this back
down to around 29k. arch/x86/entry/vdso/Makefile adds this flag too.