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Date: Wed, 21 Nov 2012 15:07:22 -0500
From: Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH v3 4/4] kexec, x86_64: Load bzImage64 above 4G
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To: Yinghai Lu <yinghai@kernel.org>
Cc: Haren Myneni <hbabu@us.ibm.com>, Simon Horman <horms@verge.net.au>, kexec@lists.infradead.org, "Eric W. Biederman" <ebiederm@xmission.com>, "H. Peter Anvin" <hpa@zytor.com>

On Wed, Nov 21, 2012 at 11:50:56AM -0800, Yinghai Lu wrote:
> On Wed, Nov 21, 2012 at 6:50 AM, Vivek Goyal <vgoyal@redhat.com> wrote:
> > On Tue, Nov 20, 2012 at 11:31:38PM -0800, Yinghai Lu wrote:
> >
> > [..]
> >> +int bzImage64_probe(const char *buf, off_t len)
> >> +{
> >> +     const struct x86_linux_header *header;
> >> +     if ((uintmax_t)len < (uintmax_t)(2 * 512)) {
> >> +             if (probe_debug) {
> >> +                     fprintf(stderr, "File is too short to be a bzImage!\n");
> >> +             }
> >> +             return -1;
> >> +     }
> >> +     header = (const struct x86_linux_header *)buf;
> >> +     if (memcmp(header->header_magic, "HdrS", 4) != 0) {
> >> +             if (probe_debug) {
> >> +                     fprintf(stderr, "Not a bzImage\n");
> >> +             }
> >> +             return -1;
> >> +     }
> >> +     if (header->boot_sector_magic != 0xAA55) {
> >> +             if (probe_debug) {
> >> +                     fprintf(stderr, "No x86 boot sector present\n");
> >> +             }
> >> +             /* No x86 boot sector present */
> >> +             return -1;
> >> +     }
> >> +     if (header->protocol_version < 0x020C) {
> >> +             if (probe_debug) {
> >> +                     fprintf(stderr, "Must be at least protocol version 2.12\n");
> >> +             }
> >> +             /* Must be at least protocol version 2.12 */
> >> +             return -1;
> >> +     }
> >> +     if ((header->loadflags & 1) == 0) {
> >> +             if (probe_debug) {
> >> +                     fprintf(stderr, "zImage not a bzImage\n");
> >> +             }
> >> +             /* Not a bzImage */
> >> +             return -1;
> >> +     }
> >> +     if (!(header->xloadflags & 1)) {
> >> +             if (probe_debug) {
> >> +                     fprintf(stderr, "Not a bzImage64\n");
> >> +             }
> >> +             /* Must be LOADED_ABOVE_4G */
> >> +             return -1;
> >> +     }
> >
> > So how do I force a 16bit or 32bit entry using a bzImage64?
> 
> kexec -t bzImage -l ....
> will load low and use 32bit entry.
> 
> kexec -t bzImage64 -l ...
> kexec -l ...
> will try to load high and use 64bit entry.

Also bzImage64 is not really a new image format. It is just enhancement
of bzImage format. We keep on doing extention of bzImage and don't call it
a new image format. I am not sure how good an idea it is to export the
notion of new image type bzImage64 to user.

Thanks
Vivek

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