Date: Mon, 17 Mar 2008 15:30:04 GMT From: Peter Grehan <grehan@FreeBSD.org> To: freebsd-ppc@FreeBSD.org Subject: Re: powerpc/121407: [panic] Won't boot up; strange error message. Message-ID: <200803171530.m2HFU4wg079498@freefall.freebsd.org>
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The following reply was made to PR powerpc/121407; it has been noted by GNATS.
From: Peter Grehan <grehan@freebsd.org>
To: bug-followup@FreeBSD.org, phillip-murphy@hotmail.com
Cc:
Subject: Re: powerpc/121407: [panic] Won't boot up; strange error message.
Date: Mon, 17 Mar 2008 08:12:32 -0700
I have some more info on this. The PC that it fails at is in
moea_bootstrap(),
4d3f98: 60 00 00 00 nop
4d3f9c: 60 00 00 00 nop
4d3fa0: 7d 30 83 a6 mtibatu 0,r9
4d3fa4: 7c 11 83 a6 mtibatl 0,r0
>>4d3fa8: 4c 00 01 2c isync
4d3fac: 7d 38 83 a6 mtdbatu 0,r9
4d3fb0: 7c 19 83 a6 mtdbatl 0,r0
4d3fb4: 4c 00 01 2c isync
4d3fb8: 3d 20 80 00 lis r9,-32768
4d3fbc: 61 29 1f fe ori r9,r9,8190
4d3fc0: 3c 00 80 00 lis r0,-32768
.. and this corresponds to RELENG_7
powerpc/powerpc/mmu_oea.c:moea_bootstrap()
/*
* Use an IBAT and a DBAT to map the bottom segment of memory
* where we are.
*/
batu = BATU(0x00000000, BAT_BL_256M, BAT_Vs);
batl = BATL(0x00000000, BAT_M, BAT_PP_RW);
__asm (".balign 32; \n"
"mtibatu 0,%0; mtibatl 0,%1; isync; \n"
"mtdbatu 0,%0; mtdbatl 0,%1; isync"
:: "r"(batu), "r"(batl));
The problem is that the instruction BAT register 0 is being updated
underneath code that will then be mapped by it, resulting in races
between the G3's instruction decoder, instruction pipe, and the
registers being used for i-translation. I saw this problem on all G3's
on 6.0, and fixed it after a lot of experiments by cache-aligning the
instruction (the .balign directive, and the source of the nop's in the
disassembly).
7.0 boots fine on my B&W G3, and 450MHz G3 iMac. However, it appears
that there is at least one system out there that still has an issue with
this code :(
I'll try and fix this once and for all by disabling instruction
translation around the IBAT update, and then re-enabling it.
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