Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)

From: Avi Kivity
Date: Wed Jan 20 2010 - 07:23:20 EST

On 01/20/2010 11:57 AM, Peter Zijlstra wrote:
On Wed, 2010-01-20 at 11:43 +0200, Avi Kivity wrote:
1. Write a trace entry into shared memory, trap into the kernel on overflow.
2. Trap if a condition is satisfied (fast watchpoint implementation).
So now you want to consume more of a process' address space to store
trace data as well?

Yes. I know I'm bad.

Not to mention that that process could wreck the
trace data rendering it utterly unreliable.

It could, but it also might not. Are we going to deny high performance tracing to users just because it doesn't work in all cases?

Note this applies to any kind of monitoring or debugging technology. A process can be influenced by the debugger and render any debug info you get out of it unreliable. One non-timing example is a process using a checksum of its text as an input to some algorithm.

error compiling committee.c: too many arguments to function

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