Using stapdyn to probe child processes of the target?

[Frank Ch. Eigler]

serhei.etc wrote:

> [...] If I'm using kernel systemtap, I can just target
> cc1 directly, for example:
>
> stap -ve 'probe
> process("/usr/libexec/gcc/x86_64-redhat-linux/6.3.1/cc1").insn {
> counter<<<1 } global counter probe end { printf("%d calls\n",
> @count(counter)) }' -c "gcc test/widget3.c"
> [...]

As you noticed, this is a terribly inefficient way of counting
instructions.  You could try instead perfcounters to estimate.  It
samples an instruction perfcounter for a target process (thread) at
every function-return, and since this number only gets larger, it will
eventually get close to the overall count as the process exits.
(We should be able to sample that counter at a process.end type event
too, but our implementation is limited.)

% cat > countem.stp << 'END'
@define cc1 %( "/usr/libexec/gcc/x86_64-redhat-linux/6.3.1/cc1" %)
global insns
probe perf.hw.instructions.process(@cc1).counter("foo") {}
probe process(@cc1).function("*").return {
   insns[execname(),tid()] = @perf("foo") // implicit max()
}
END

% sudo stap countem.stp -c "gcc ...."
insns["cc1",2102]=0x367fb494
%

- FChE