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SubjectRe: [PATCH 1/23] Make register values available to panic notifiers
Martin Schwidefsky wrote:
> On Mon, 12 Apr 2010 13:27:45 +0100
> Russell King <rmk@arm.linux.org.uk> wrote:
>
>
>> On Sun, Apr 11, 2010 at 11:06:09PM -0700, David VomLehn wrote:
>>
>>> This patch makes panic() and die() registers available to, for example,
>>> panic notifier functions. Panic notifier functions are quite useful
>>> for recording crash information, but they don't get passed the register
>>> values. This makes it hard to print register contents, do stack
>>> backtraces, etc. The changes in this patch save the register state when
>>> panic() is called and introduce a function for die() to call that allows
>>> it to pass in the registers it was passed.
>>>
>> Can you explain why you want this?
>>
>> I'm wondering about the value of saving the registers; normally when a panic
>> occurs, it's because of a well defined reason, and not because something
>> went wrong in some CPU register; to put it another way, a panic() is a
>> more controlled exception than a BUG() or a bad pointer dereference.
>>
>
> I'm curious about the potential use case as well. So far I only wanted
> to know the registers if the panic has been triggered due to an
> unexpected fault with panic_on_oops=1 or in_interrupt()==1. If that
> happens the die() handler prints the registers. An open coded panic is
> easy to analyze, imho no need for the registers
>

Good example, because helps focus the issue. In recording a subset of
kernel state
information from an embedded system for collection at a central point.
The register
values printed by die() are printed to the console, where they
disappear. One of the
things in this patch involves passed a pointer to those die() registers
to a register
panic notifier handler. So, there is a path to where panic handlers are
called from
die() and another one from panic() and this patch makes register values
available in
both cases.


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