[Bug runtime/11852] Nice to have - structure name aliasing/changing

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2010-08-03 11:35 -------
> I added both options to the same probe statement.
> The first option works and does not break anything.

Great, that should be the first method we anticipated a stap user would try it.

> The second option gives me:
> semantic error: type definition 'pmaplist<rpc/pmap_prot.h>' not found: 
> identifier '@cast' at ./portmap3.stp:70:37

OK, you must be running a version of systemtap from 2009.  A newer one
should give you this facility.

> As I see it there are several issues here:
> 1) In which cases is GURU mode required?

Mainly when you require access to data that there is no other way
to get to; or when accessing it requires complex kernel interaction
such as locks or kernel API calls.

> 2) When it is required, when does the method I suggested break?

The basic problem is as Josh stated: embedded-C code runs in kernel
space and is thus compiled against kernel headers with kernel
assumptions.  There are many different assumptions in kernel space
beyond a different namespace of struct types.  Usage of floats,
struct padding, argument passing ABIs are just a few that come to mind.

> 3) Can this method be standardized in any way?

If the script-language-level constructs ($foo->bar, @cast()) are truly
not sufficient for a real scenario, we can try harder to figure it out.


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http://sourceware.org/bugzilla/show_bug.cgi?id=11852

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