Profiling C++ with Google Perf tools and Dynamic Libraries

Question

I'm trying to profile a C++ application, that I did not write, to get a sense for where the major computation points are. I'm not a C++ expert and even less so C++ debugging/profiling expert. I believe I am running into a (common?) problem with dynamic libraries.

I compile link to Google CPU Profiler using (OS X, G++):

env LIBS=-lprofiler ./configure
make
make install

I then run profile the installed application (jags) with:

env CPUPROFILE=./jags.prof /usr/local/bin/jags regression.cmd
pprof /usr/local/bin/jags jags.prof

Unfortunately, I get the error:

pprof /usr/local/bin/jags jags.prof Can't exec "objdump": 
No such file or directory at /usr/local/bin/pprof line 2833.

objdump /System/Library/Frameworks/Accelerate.framework/Versions/A/
Frameworks/vecLib.framework/Versions/A/libLAPACK.dylib: No such file or directory

The program dynamically links to libLAPACK.dylib. So prof does not seem to understand it (?). I thought about trying to statically link, but the documents associated with the program say that it is impossible to statically link in LAPACK or BLAS (two required libraries).

Is there a way to have the profiler ignore libLAPACK? I'm okay if it doesn't sample within libLAPACK. Or how might I get profiling to work?

Answer 1

I don't see a clean way to do it, but maybe there's a hacky workaround -- what happens if you hack the pprof perl script (or better a copy thereof;-), line 2834, so that instead of calling error it emits the message and then does return undef;?

Answer 2

This error was caused by jags being a shell script, that subsequently called profilable code.

pprof /usr/local/bin/REAL_EXEC jags.prof

fixes the problem.

Answer 3

If you're profiling on OSX, the Shark tool is really great as well. It's very simple to use, and has worked out of the box for me when I've tried it.