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Date: Thu, 02 Sep 2010 16:08:15 +0300
From: Andriy Gapon <avg@freebsd.org>
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Subject: Re: problem with amd64 minidump
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on 02/09/2010 13:10 Andriy Gapon said the following:
> 
> Not sure if this is some local issue or a problem in FreeBSD code.
> I remember minidumps working perfectly well for me, but now I can not get data
> from them.
> Example:
> dmesg -M /var/crash/vmcore.4
> dmesg: _kvm_vatop: direct map address 0xffffff012fffffe0 not in minidump
> dmesg: kvm_read: invalid address (0xffffff012fffffe0)

Not sure if it can help, but it seems that this virtual address in DMAP
corresponds to a physical address in the last page of RAM.
Do we use that for anything special?  Message buffer?
I had a quick look at getmemsize() function in sys/amd64/amd64/machdep.c and it
looks like the following code in the function could be doing just that:

Maxmem = atop(phys_avail[pa_indx]);

/* Trim off space for the message buffer. */
phys_avail[pa_indx] -= round_page(MSGBUF_SIZE);

/* Map the message buffer. */
msgbufp = (struct msgbuf *)PHYS_TO_DMAP(phys_avail[pa_indx]);

Oh, and yeah:
(gdb) p msgbufp
$4 = (struct msgbuf *) 0xffffff012fffffe0

But we do dump the message buffer.
But somehow its dmap address is not resolved correctly.

This should ring a bell for someone knowledgeable of minidump and libkvm code, I
believe.

> Needless to say kgdb refuses to work with that core too.
> 
> With kgdb on live system I can access that address:
> (gdb) x/a 0xffffff012fffffe0
> 0xffffff012fffffe0:     0xffffff012ffe0000



-- 
Andriy Gapon