Date: Wed, 17 Mar 1999 21:37:00 +0000 (GMT) From: Doug Rabson <dfr@nlsystems.com> To: Stefan Reinauer <stepan@suse.de> Cc: freebsd-alpha@freebsd.org Subject: Re: faked BSD disklabel to boot from SRM Message-ID: <Pine.BSF.4.05.9903172129040.47099-100000@herring.nlsystems.com> In-Reply-To: <Pine.LNX.4.05.9903172216070.28612-100000@Galois.suse.de>
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On Wed, 17 Mar 1999, Stefan Reinauer wrote: > On Wed, 17 Mar 1999, Doug Rabson wrote: > > > I thought about this too a long time ago. Unfortunately the fields in the > > first sector which SRM uses to point at the bootstrap overlaps with the > > MSDOS partition table. It just isn't possible to make a disk bootable > > from both SRM and AlphaBIOS (which is why I wanted to do it). > > Hmm.. is there some documentation about that first sector with the pointer > to bootstrap overlaps? Or is this part of the bsd disklabel structure > starting with the magic number 0x82564557? I have multiple versions of > this structure now but none is documented.. :) The only documentation which I have to had for the disklabel structure is the code... There is documentation for the SRM bootstrap process (which includes a description of the required fields in the first disk sector) in "Alpha AXP Architecture Reference Manual 2nd Edition", Part III.3. From my copy: Reserved (VAX Compatibility) :BB Reserved (Expansion) :+136 Reserved :+472 Count (LBNs) :+480 Starting LBN :+488 Flags :+496 Checksum :+504 :+512 SRM doesn't seem to care much about the reserved fields (and the BSD disklabel lives right inside where the VAX boot block would have been I think). The main thing is that the bootstrap lives in a contiguous section of disk with the start sector given by "Starting LBN" and the size in sectors given by "Count (LBNs)". The "Flags" field must be zero and the "Checksum" field is a simple 64bit sum of the first 63 64bit words in the block. -- Doug Rabson Mail: dfr@nlsystems.com Nonlinear Systems Ltd. Phone: +44 181 442 9037 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message
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