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Re: visit_target_symbol() for derived_probes

I have tried to replicate what the dwarf and mark probes do as far as handling target variable ($variable) for $counter in the perfmon probes. The perfmon probe needs a read only value indicating which counter is being used for that event. From what I understand discussing this with Frank and examining the code here are the things that need to be done:

-allocate space for the variable
-generate a declaration for the synthesized function
-generate C code for the synthesized function
-replace the $target var use with a call to the synthesized function

It appears that I am not getting the function built in the latest patch that is saved in bz#909. Where exactly does the creation of the synthesized function occur for the dwarf and mark probes? I seem to be missing the corresponding operation. Later the code gets a seg fault in symresolution_info::visit_symbol(). Thus, for the this short example:

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);

The following happens:

(gdb) run -p4 -k ../elapsed.stp
Starting program: /home/wcohen/research/profiling/systemtap_perfmon/install/bin/stap -p4 -k ../elapsed.stp
while searching for arity 0 function:
semantic error: unresolved function call: identifier '$counter' at ../elapsed.stp:4:51

Program received signal SIGSEGV, Segmentation fault.
0x000000000042e60f in symresolution_info::visit_symbol (this=0x7fffd7223960,
at /usr/lib/gcc/x86_64-redhat-linux/4.0.2/../../../../include/c++/4.0.2/ext/mt_allocator.h:585
585 { ::new(__p) _Tp(__val); }
(gdb) where
#0 0x000000000042e60f in symresolution_info::visit_symbol (
this=0x7fffd7223960, e=0xb34790)
at /usr/lib/gcc/x86_64-redhat-linux/4.0.2/../../../../include/c++/4.0.2/ext/mt_allocator.h:585
#1 0x000000000041d221 in traversing_visitor::visit_assignment (
this=0x7fffd7223960, e=0xb34510) at ../src/staptree.cxx:1434
#2 0x000000000041f5af in assignment::visit (this=0xb34510, u=0x7fffd7223960)
at ../src/staptree.cxx:1070
#3 0x00000000004292dd in symresolution_info::visit_block (
this=0x7fffd7223960, e=0xb34370) at ../src/elaborate.cxx:973
#4 0x000000000042d8e4 in semantic_pass_symbols (s=@0x7fffd7223d50)
at ../src/elaborate.cxx:891
#5 0x00000000004307e1 in semantic_pass (s=@0x7fffd7223d50)
at ../src/elaborate.cxx:916
#6 0x000000000040830e in main (argc=Variable "argc" is not available.
) at ../src/main.cxx:468


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