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* Application name: probe context information ariables
* Contact: fche
* Motivation: let probes know where/how they were fired; introspective
probe handlers
* Background: discussions on mailing lists
* Target software: various
* Type of description: tapset variables
* Interesting probe points: n/a
* Interesting values:
$pp_alias: string: the string specification of the probe point, as found
in the original .stp file, before alias and other
expansion
$pp: string: representation of this probe point, after alias and wildcard
expansion
$pp_function: string: source function (if available)
$pp_srcfile: string: source file name (if available)
$pp_srcline: number: line number in source file (if available)
$function[pc]: string: function name containing given address
$module[pc]: string: kernel module name containing given address
$address[sym]: number: base address of given function symbol
$pc: number: PC snapshot at invocation
$stack[depth]: number: PC of caller at given depth, if available
* Dependencies:
Debug-info files
* Restrictions:
The $pp series of variables are computed at translation time, and thus
are only applicable to those probes that have related debug-info points.
$pc should be directly available.
The $function series of read-only pseudo-arrays are calculated at
run time, from symbol table information passed in some way.
$stack[0] might take some probing in the registers, or (eek!) on the
target stack frame. Conservatively returning 0 instead may be okay.
* Data collection:
Several of the variables are translation-time constants, so these don't
have run-time collection needs.
For a kernel/module probe, $function[] could be computed from the kallsyms
lookup functions. Alternately, the translator could emit a copy of the
target symbol table into the probe C code, which $function[] could
search. The $stack[] elements would be served by the runtime on a
best-effort basis.
* Data presentation:
n/a: variables are simple
* Competition:
unknown
* Cross-references:
http://sources.redhat.com/ml/systemtap/2005-q2/msg00395.html
http://sources.redhat.com/ml/systemtap/2005-q2/msg00281.html
* Associated files:
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