Re: visit_target_symbol() for derived_probes

[fche at redhat dot com (Frank Ch. Eigler)]

wcohen wrote:

> [...]
> global handle
> global cycles_start, cycles_end
> probe perfmon.counter("CPU_CLK_UNHALTED") {handle= $counter}
                                                    ^^^
> probe begin { cycles_start = read_counter(handle) }
> probe end
> {
>    cycles_end = read_counter(handle);
>    elapsed = cycles_start - cycles_end;
>    printf("%d cycles\n", elapsed);
> }

Yeah, plausible.

> I have been looking at how target symbols and $return are handled in
> the dwarf_derived_probe. [...]

Look also at marker_derived_probe for another implementation with a
different flavour.

> typeresolution_info::visit_target_symbol (target_symbol* e) [...]
>    throw semantic_error("unresolved target-symbol expression", e->tok);

Yes, this detects the failure-to-process scenario.

> How is the node in the tree generated for the target symbol?

The target_symbol node is generally replaced with a synthesized getter
or setter function call: mark_var_expanding_copy_visitor::visit_target_symbol


- FChE