* [Bug translator/18431] New: runtime function overloading facility
@ 2015-05-19 15:46 fche at redhat dot com
2015-09-23 21:54 ` [Bug translator/18431] " ajakop at redhat dot com
0 siblings, 1 reply; 2+ messages in thread
From: fche at redhat dot com @ 2015-05-19 15:46 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=18431
Bug ID: 18431
Summary: runtime function overloading facility
Product: systemtap
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: translator
Assignee: systemtap at sourceware dot org
Reporter: fche at redhat dot com
Target Milestone: ---
It turns out to be necessary to have a facility that allows end-user scripts to
call generic functions like jstack(), while multiple alternative
implementations available in the tapset library. The method of choosing
between the alternatives must be done at run-time (since it's run-time state
such as "which VM is this thread running in?" that decides), so we're talking
about a control-flow extension rather than translate-time processing like c++
overloading.
Possible syntax at call site: foo() - i.e., no visible change.
Possible syntax at definitions:
function foo () {
...
... if (condition) next; ...
...
}
Possible semantics: for a call, expand to:
- at translate time, construct sorted list of functions that match call
- prefer end-user script highest/first, to provide override capability
- sort others somehow (maybe have explicit ranking like begin(N) probes)
- pseudocode for generated call:
- evaluate PARAMS into temporary variable, for side-effects
- foreach FUNCTION in ALTERNATIVES
- call FUNCTION(PARAM_copies)
- if it returned normally or with an exception/error, done
- else it exited with a 'next' (a new flag in the context structure);
continue looping
- if all alternatives functions exited with 'next', throw an exception
- (All this can be optimized to current code etc, if the translator
detects no 'next' statements in the function body. Ignore
transitively called functions.)
- pseudocode for function-side next: easy peasy
- set function-context nexted-out flag
- return
In this model, any side-effects caused by the alternative functions, before
they run 'next', will persist.
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* [Bug translator/18431] runtime function overloading facility
2015-05-19 15:46 [Bug translator/18431] New: runtime function overloading facility fche at redhat dot com
@ 2015-09-23 21:54 ` ajakop at redhat dot com
0 siblings, 0 replies; 2+ messages in thread
From: ajakop at redhat dot com @ 2015-09-23 21:54 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=18431
Abe Jakop <ajakop at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ajakop at redhat dot com
Assignee|systemtap at sourceware dot org |ajakop at redhat dot com
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