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All,
I attach a small patch to create a console log that uses the
SMRAM area. This allows OOPS output to be captured and saved across a
reboot.
The conslog.txt file has a brief explanation of how it works. There are
some important limitations:
1) It only works on Intel platforms
2) It only works with a motherboard with a modern Intel chipset
(includes P-II/P-III boards)
It is not for everyone. I build it as a module. It works for me.
The 10 cent summary is that it creates an internal console log,
exposed through /proc/conslog. The console log survives reboots.
Enjoy,
Philip
-- Philip Gladstone +1 781 530 2461 Axent Technologies, Waltham, MA --------------B44F1F641E90E51324533406 Content-Type: application/x-gzip; name="conslog.pf.gz" Content-Transfer-Encoding: base64 Content-Disposition: inline; filename="conslog.pf.gz"H4sIAK17ejcAA60aa1fa2PYz/opd2iqRoAFtq6KuKtKWGcUu0E7ndrqyMBw0qyHhJsHinet/ v3ufR3LywNI7ZToYzmO/X2efNBoN2B6z+21/7nmVi8CHM+bAThNaOweWhf+guf9mf61er4Pn +vPF9jh071kYbTt3o3DbCfzIC263nMofbAy/zX3YwQ2vD5p7B692cOf+/trbt9CwTAvqTXO3 acHbt2v17c1f81mrb0InmD2E7u1dTNh2G/i1Byefu/0ruGLOnR8gdS6LTOj5zhaceB7wxRGE LGLhPRtvAX4I0q/5bK/Vn7u+483HDA6FwKbBeO6xrbvjtXpxMorHYzbhk/kpkrIb+KVz8cOM RaUzszBw7Imam8B5r3/92f7UHQx7l327c3nWhUNo7jRf7e0WN9+4QbTTEnuRLNdnYNuzUW1h gPrgsz55XzLJvIjpsEfRdHs+chwW5UmmmdnolpVyQrYVSMEphJy7kN26UcxCe/zgj6aukx0l AvyxOykRjeOW4HcDqRouLx8RIVuu78aTue/orKoxwfAixZMuuuheXA7+tC9O3vc6ANZizEbj G8YmOvCPnZ591v3U63Tt3pnd6191z+291u7uzvnnFNATixDsm+aelUH/I9Cnn+2T9x9XAC8W chT7P4tiJfACdKtMeABn9nnndyDBNa3s+OXHbp/Gd62cuO3Tk2FXmR83R2txY+HHyC4b9v6V 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This is a brief note that describes the implementation of the console logger.
The basic idea is that all console output is saved in a circular buffer that is hidden where it is not destroyed over a reboot.
This particular version of the code uses the SMRAM area at 0xb0000. This area is normally occupied by a video card, but by fiddling with the appropriate Intel Northbridge chip, access to real RAM can be enabled. Happily, many BIOS implementations are either too dumb, or smart enough, not to destroy this memory area during the power-on memory test.
I'd be interested in finding out which platforms this works on!
Once started, the logger creates /proc/conslog which contains the console log. The size of the log is 65k, which is ample for seeing any OOPSen before a reboot.
Installation:
Apply the attached patch with patch -p1 in your linux root. (Tested with 2.2.9).
Run make config, and on the character devices page, turn on the 'log to SMRAM' option. You can choose either to build it into the kernel, or to have it as a module.
Now build your kernel/modules.
If you build it as a module, then you can just insmod conslog.o on a running system. Note that you must have it loaded to record console output -- there is no point in loading it *after* a crash.
Licensing:
Currently this is *NOT* under the GPL. It remains copyright Axent Technologies. I am exploring the possibility to make it available under the GPL.
All use is at own risk etc. Axent Technologies assumes no liability for any damage etc.
Bugs:
It only works on Intel platforms (owing to the nasty embedded cache flushing instructions).
It only works with a limited set of motherboard chipsets.
It doesn't work on all platforms -- some BIOSes clear out SMRAM memory, and some lock the SMRAM area so that it cannot be accessed.
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