Messages in this thread |  | | Subject | Re: Bug#640964: linux-image-3.1.0-rc4-486: BUG() triggered on XO-1 hardware | | From | Ben Hutchings <> | | Date | Fri, 09 Sep 2011 03:41:19 +0100 |
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On Thu, 2011-09-08 at 17:46 -0700, Andres Salomon wrote: > Package: linux-image-3.1.0-rc4-486 > Version: 3.1.0~rc4-1~experimental.1 > Severity: normal > > During boot on an OLPC XO-1, I encounter the following problem. I > believe it's the statement BUG_ON(a->cpuid >= NCAPINTS*32), though I'm > not staring at an exact copy of linux-2.6 source. [...]
Agreed.
Variable a is in the EBX register, value 0xc143c668. Looking at a dump of this kernel image, the __alt_instructions array starts with:
c143c638 7e51bcff 1c050000 1a000503 7d51bcff ~Q..........}Q.. c143c648 13050000 1a000503 6653bcff 0a050000 ........fS...... c143c658 19000503 00000000 ce55bcff 00000000 .........U...... c143c668 9a000200 cf55bcff f1040000 e4000303 .....U.......... ...
Converting back to C structures:
/* instr_offset, repl_offset, cpuid, instrlen, replacementlen */ { 0xffbc517e, 0x0000051c, 0x001a, 0x05, 0x03 }, { 0xffbc517d, 0x00000513, 0x001a, 0x05, 0x03 }, { 0xffbc5366, 0x0000050a, 0x0019, 0x05, 0x03 }, { 0x00000000, 0xffbc55ce, 0x0000, 0x00, 0x00 }, { 0x0002009a, 0xffbc55cf, 0x04f1, 0x00, 0x00 }, ...
Oops, we have 4 bytes of zeroes between what should be elements 2 and 3. That results in __alt_instructions[4].cpuid == 0x04f1 which trips the BUG check. This is nothing OLPC-specific; it's going to happen on any machine trying to boot this image.
So the question is, where does that padding come from?
Ben.
-- Ben Hutchings I say we take off; nuke the site from orbit. It's the only way to be sure. [unhandled content-type:application/pgp-signature] |  |