Re: [PATCH] Linux Kernel Markers

Martin Bligh
2006-09-19T19:25:29Z

Mathieu Desnoyers wrote:
> * Vara Prasad (prasadav@us.ibm.com) wrote:
>
>>Martin Bligh wrote:
>>
>>
>>>[...]
>>>Depends what we're trying to fix. I was trying to fix two things:
>>>
>>>1. Flexibility - kprobes seem unable to access all local variables etc
>>>easily, and go anywhere inside the function. Plus keeping low overhead
>>>for doing things like keeping counters in a function (see previous
>>>example I mentioned for counting pages in shrink_list).
>>>
>>
>>Using tools like systemtap on can consult DWARF information and put
>>probes in the middle of the function and access local variables as well,
>>that is not the real problem. The issue here is compiler doesn't seem to
>>generate required DWARF information in some cases due to optimizations.
>>The other related problem is when there exists debug information, the
>>way to specify the breakpoint location is using line number which is not
>>maintainable, having a marker solves this problem as well. Your proposal
>>still doesn't solve the need for markers if i understood correctly.
>
> His implementation makes a heavy use of a marker mechanism : this is exactly
> what permits to create the instrumented objects from the same source code, but
> with different #defines.

I don't think it ties us to markers, though I think they're superior for
maintaintance, personally. It could equally well be an out of tree
normal flat patch with all the tracing in, which would make Andrew
happy, even if I think it sucks ;-)

M.