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Date: Thu, 21 Nov 2013 15:00:19 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20131121130019.GA14894@redhat.com>
References: <20131121120822.GA23602@redhat.com>
	<20131121132413.0af9a66d@gondolin>
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Subject: Re: [Qemu-devel] [PATCH for-1.7] s390x: fix flat rom load on 32 bit
 systems
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To: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: Alexander Graf <agraf@suse.de>, Dominik Dingel <dingel@linux.vnet.ibm.com>, qemu-devel@nongnu.org, Christian Borntraeger <borntraeger@de.ibm.com>, Andreas =?iso-8859-1?Q?F=E4rber?= <afaerber@suse.de>, Richard Henderson <rth@twiddle.net>

On Thu, Nov 21, 2013 at 01:24:13PM +0100, Cornelia Huck wrote:
> On Thu, 21 Nov 2013 14:08:22 +0200
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > pc-bios/s390-zipl.rom is a flat image so it's expected that
> > loading it as elf will fail.
> > It should fall back on loading a flat file, but doesn't
> > on 32 bit systems, instead it fails printing:
> >     qemu: hardware error: could not load bootloader 's390-zipl.rom'
> > 
> > The result is boot failure.
> > 
> > The reason is that a 64 bit unsigned interger which is set
> > to -1 on error is compared to -1UL which on a 32 bit system
> > with gcc is a 32 bit unsigned interger.
> > Since both are unsigned, no sign extension takes place and
> > comparison evaluates to non-equal.
> > 
> > There's no reason to do clever tricks: -1 will cause
> > sign extension to happen correctly automatically.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  hw/s390x/ipl.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/hw/s390x/ipl.c b/hw/s390x/ipl.c
> > index d69adb2..88115e9 100644
> > --- a/hw/s390x/ipl.c
> > +++ b/hw/s390x/ipl.c
> > @@ -80,7 +80,7 @@ static int s390_ipl_init(SysBusDevice *dev)
> > 
> >          bios_size = load_elf(bios_filename, NULL, NULL, &ipl->start_addr, NULL,
> >                               NULL, 1, ELF_MACHINE, 0);
> > -        if (bios_size == -1UL) {
> > +        if (bios_size == -1) {
> >              bios_size = load_image_targphys(bios_filename, ZIPL_IMAGE_START,
> >                                              4096);
> >              ipl->start_addr = ZIPL_IMAGE_START;
> 
> Makes sense, but doesn't the kernel loader just below suffer from just
> the same problem?

Yes, v2 fixes this.