Re: visit_target_symbol() for derived_probes

[William Cohen <wcohen at redhat dot com>]

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,
    e=0xb34790)
    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


-Will