linux-kernel - Re: kexec, x86/purgatory: Cleanup the unholy mess

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Date:   Fri, 10 Mar 2017 15:31:48 +0100
From:   Mike Galbraith <efault@....de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Borislav Petkov <bp@...en8.de>, "Tobin C. Harding" <me@...in.cc>,
        LKML <linux-kernel@...r.kernel.org>,
        Nicholas Mc Guire <der.herr@...r.at>,
        Vivek Goyal <vgoyal@...hat.com>, x86@...nel.org
Subject: Re: kexec, x86/purgatory: Cleanup the unholy mess

On Fri, 2017-03-10 at 14:57 +0100, Thomas Gleixner wrote:
> On Fri, 10 Mar 2017, Mike Galbraith wrote:
> > On Fri, 2017-03-10 at 13:17 +0100, Thomas Gleixner wrote:
> > > The purgatory code defines global variables which are referenced via a
> > > symbol lookup in the kexec code (core and arch).
> > > 
> > > A recent commit addressing sparse warning made these static and thereby
> > > broke kexec file.
> > > 
> > > Why did this happen? Simply because the whole machinery is undocumented and
> > > lacks any form of forward declarations. The variable names are unspecific
> > > and lack a prefix, so adding forward declarations creates shadow variables
> > > in the core code. Aside of that the code relies on magic constants and
> > > duplicate struct definitions with no way to ensure that these things stay
> > > in sync.
> > > 
> > > Unbreak kexec and cleanup the mess by:
> > > 
> > >  - Adding proper forward declarations and document the usage
> > >  - Use the proper common defines instead of magic constants
> > >  - Add a purgatory_ prefix to have a proper name space
> > >  - Use ARRAY_SIZE() instead of a homebrewn reimplementation
> > > 
> > > Fixes: 72042a8c7b01 ("x86/purgatory: Make functions and variables static")
> > 
> > Well, almost fixes.
> > 
> > [   15.118820] kexec: symbol 'purgatory_sha_regions' in common section
> > [   15.119187] kexec-bzImage64: Loading purgatory failed
> 
> Bah. /me goes to investigate.

Stuffing the lot into .kexec-purgatory worked.

---
 arch/x86/purgatory/purgatory.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/arch/x86/purgatory/purgatory.c
+++ b/arch/x86/purgatory/purgatory.c
@@ -16,13 +16,13 @@
 #include "sha256.h"
 #include "../boot/string.h"
 
-unsigned long purgatory_backup_dest;
-unsigned long purgatory_backup_src;
-unsigned long purgatory_backup_sz;
+unsigned long purgatory_backup_dest __section(.kexec-purgatory);
+unsigned long purgatory_backup_src __section(.kexec-purgatory);
+unsigned long purgatory_backup_sz __section(.kexec-purgatory);
 
-u8 purgatory_sha256_digest[SHA256_DIGEST_SIZE];
+u8 purgatory_sha256_digest[SHA256_DIGEST_SIZE] __section(.kexec-purgatory);
 
-struct kexec_sha_region purgatory_sha_regions[KEXEC_SEGMENT_MAX];
+struct kexec_sha_region purgatory_sha_regions[KEXEC_SEGMENT_MAX] __section(.kexec-purgatory);
 
 /*
  * On x86, second kernel requries first 640K of memory to boot. Copy