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Re: Using hardware watchpoint for applications debugging

To: Nigel Stephens <>
Subject: Re: Using hardware watchpoint for applications debugging
From: Ralf Baechle <>
Date: Thu, 30 Mar 2006 19:37:42 +0100
Cc: colin <>,
In-reply-to: <>
Original-recipient: rfc822;
References: <024c01c65337$63931c90$> <> <002d01c6539f$d040a200$> <>
User-agent: Mutt/
On Thu, Mar 30, 2006 at 11:49:22AM +0100, Nigel Stephens wrote:

> They're variable, but not very variable: the PID->ASID mapping will only
> change when the ASIDs roll over and the ASID gets reallocated to a
> different process, which will only happen after another 256 processes
> have been created. But in that case your watched process will have to be
> allocated a new ASID before it can run again. So you could, perhaps,
> modify the TLB management code to clear the Watch registers whenever an
> ASID belong to a process with watchpoints is recycled, and then
> reprogram the Watch registers when such a process is allocated a new
> ASID. Alternatively you could maintain pre-process copies of the Watch
> registers, and context switch them along with other per-process register
> state -- though that is adding context switch overhead to processes
> which don't use watchpoints, and might not be popular with the maintainer.

That's not quite true; the kernel also uses the ASID as a way to flush
a context from the TLB very quickly.


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