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Re: Linux/MIPS for DECstations...

Subject: Re: Linux/MIPS for DECstations...
From: Harald Koerfgen <>
Date: Tue, 30 Sep 1997 20:54:07 +0200 (MEST)
In-reply-to: <>
Hi Ralf,

On 30-Sep-97 Ralf Baechle wrote:


>> [swapper 0] Illegal instruction at Address <somewhere>.
>> The instruction that causes this exception is:
>> > ...
>> >reload_pgd_entries:
>> >#endif /* CONF_DEBUG_TLB */
>> >
>> >        /* Load missing pair of entries from the pgd and return. */
>> >        mfc0    k1,CP0_CONTEXT 
>> >        nop
>> >        lw      k0,(k1)           #Never causes nested exception
>> >        ^^^^^^^^^^^^^^^
>> >        mfc0    k1,CP0_EPC        # get the return PC
>> > ...
>> in arch/mips/kernel/r2300_misc.S.
>Ok, I was suspecting something like that.  That particular TLB exception
>handler has to be pretty different from the R4000 version.  It's
>doing a very trivial piece of work.  The only thing that makes it
>a bit more complicated is the fact that the TLB exception handlers
>have to be even more optimized than Microsoft's hype.  In fact the
>current handlers are all far to bulky.
>I'm not shure which source tree you're using.  Could you post the
>TLB exception handler from that tree?
>  Ralf

I am still hacking Paul's kernel. After messing around with head.S 
yesterday I restored to Paul's original head.S this evening and now I am getting
a different error message:

About to init memory
mem_init called with start_mem: 8018a018, end_mem: 82fff000
mem_init now has start_mem: 8018b000, end_mem: 82fff000
Memory: 47568k/49148k available (524k kernel code, 864k data)
About to init buffers
memsize is: 2fff000
about to vmalloc hash table
vmalloc'd hash table, addr is: c0000000
about to clear hash table
[swapper:0:00000822:1:8003aab8]do_page_fault() #2: sending SIGSEGV to swapper fo
r illegal writeaccess to
00000822 (epc == 8003aab8, ra == 80070e54)

which makes a *little* bit more sense to me. Strange, even the smallest changes
seem to produce very different effects. Uhmmm... isn't that characteristic for
chaotical behaviour? ;-)

I don't want to bother this list with kBytes of listings. If you are really
interested in the version of head.S I am presently using, you can download
it from

Thanks in advance.

(switched back to my 5000/133, this thing boots via tftp :-))

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