Reduction of guru use in systemtap war stories

[William Cohen]

Frank Ch. Eigler wrote:
> wcohen wrote:
> 
>> I am looking through the war stories and figuring out how to clean
>> things up.  [...]
> 
> Thanks.
> 
>> WSthreadCPUshare uses guru mode to determine the instruction pointer
>> value for the sample and then determine whether this value is in
>> kernel or user-space. For some 32-bit kernels this approach is not
>> correct. A better approach would be make the kernel function
>> user_mode() available in the tapsets. [...]
> 
> Indeed, please make it so!

Attached is a simple little patch for the context.stp tapset and documentation 
to "make it so." Assuming that it looks okay I will commit it.

> 
>> Some of the other war stories (WSPfiles, WSPsig, and WSPlimit) the
>> idiom to map a pid to a task struct point comes up and would be a
>> candidate to add to the tapsets. It looks like some of the other guru
>> functions in those scripts are already available and can be recast as
>> task.stp tapset functions. [...]
> 
> See bug #6525 for a probably more robust way.  The one used in some of
> that embedded-c code, find_task_by_pid(), is not safe to call from all
> contexts.

Thanks for the pointer to 6525.

>> Several of the war stories (such as WSPfiles) include header files
>> and make use of defines to extract bits/flags out of values. Seems
>> like there should be a cleaner way to make those bit values
>> available to scripts.
> 
> One possibility is to lobby the kernel to run gcc with -g3 or somesuch
> to get it to dump macro definitions into the dwarf data; then we could
> pull it out of there with $MACRO.  Sounds unlikely.

At the moment asking for -g3 sounds unlikely. The debuginfo is already large. 
Adding in all the macros is going to make the debug information even larger.

> Other ideas?

-Will

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