Profiling C application

[Scott Bennett]

Andrea Venturoli <ml at netfence.it> wrote:

> On 11/29/20 1:02 PM, Scott Bennett wrote:
> > Andrea Venturoli <ml at netfence.it> wrote:
> > 
> >> On 11/28/20 8:22 PM, Scott Bennett via freebsd-questions wrote:
> >>
> >>>        I see you already have one response at least to your question, but
> >>> perhaps a simpler one is to use a now ancient BSD UNIX tool called gprof(1),
> >>> along with the compiler option -pg.  (See the gprof(1) man page for the
> >>> details.)  Note, too, that you may want to link your program to the profiling
> >>> versions of system libraries as explained in the man page.
> >>
> >> I didn't mention gprof because it stopped working when FreeBSD switched
> >> from GCC to clang. Or, maybe, it was my fault, not being able to get it
> >> working again.
> >>
> >> That was a long time ago, however; if nowadays it's a viable solution,
> >> I'm happy to hear this.
> >>
> >       Bugzilla only turned up one PR that may have a bearing on that.  See
> > PR 198462 from 2017 and 10.1.  There's no sign that anyone, other than the poster
> > of the PR, even looked into it, an unfortunately common situation.
> >       Thank you for pointing out the problem.  Do you still have a test case you
> > could try?
>
> Sorry for answering so late...
>
> Today I need once again to profile a program and, since valgrind is 
> currently broken :-(, I decided to give gprof another shot (on 12.2/amd64).
>
> As per gprof(1), I added "-pg" to compilation and linking phase, i.e. my 
> program compiles with something like:
> c++ -c -ggdb -O0 -pg ... -o a.o a.cxx
> c++ -c -ggdb -O0 -pg ... -o b.o b.cxx
> ...
> c++ -o a.exe a.o b.o ... -lthr -pg ...
>
> When I run it, I get:
> % ./a.exe
> ld-elf.so.1: /lib/libc.so.7: Undefined symbol "__progname"
>
> gprof(1) states that "The -pg option also links in versions of the 
> library routines that are compiled for profiling". Alas, this does not 
> seem to be the case:
> ldd a.exe
> a.exe:
> 	libarchive.so.13 => /usr/local/lib/libarchive.so.13 (0x8004a0000)
> 	libboost_filesystem.so.1.72.0 => 
> /usr/local/lib/libboost_filesystem.so.1.72.0 (0x800574000)
> 	libboost_program_options.so.1.72.0 => 
> /usr/local/lib/libboost_program_options.so.1.72.0 (0x800591000)
> 	libboost_system.so.1.72.0 => /usr/local/lib/libboost_system.so.1.72.0 
> (0x8005f1000)
> 	libcrypto.so.111 => /lib/libcrypto.so.111 (0x8005f5000)
> 	libexpat.so.1 => /usr/local/lib/libexpat.so.1 (0x8008e7000)
> 	liblzo2.so.2 => /usr/local/lib/liblzo2.so.2 (0x800914000)
> 	liblzma.so.5 => /usr/lib/liblzma.so.5 (0x800944000)
> 	liblz4.so.1 => /usr/local/lib/liblz4.so.1 (0x800970000)
> 	libbz2.so.4 => /usr/lib/libbz2.so.4 (0x80099e000)
> 	libz.so.6 => /lib/libz.so.6 (0x8009b4000)
> 	libc.so.7 => /lib/libc.so.7 (0x8009d0000)
> 	libc++.so.1 => /usr/lib/libc++.so.1 (0x800dc6000)
> 	libcxxrt.so.1 => /lib/libcxxrt.so.1 (0x800e93000)
> 	libm.so.5 => /lib/libm.so.5 (0x800eb5000)
> 	libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x800ee7000)
> 	libthr.so.3 => /lib/libthr.so.3 (0x800f01000)
> 	libmd.so.6 => /lib/libmd.so.6 (0x800f2e000)
>
> I think I should change "-lthr" to "-lthr_p", but that does not make any 
> difference. Ditto if I add "-lc_p": apparently these are ignored.

     Actually, I think it should work even using non-profiling libraries, but
you wouldn't see any data gathered regarding calls within those libraries.
>
> What am I doing wrong?
>
> BTW, would solving this be enough or would I later hit the fact that I'm 
> using third party libraries (e.g. boost) which are not compiled with "-pg"?
>
     See above.
     I am afraid I can be of little help.  The last time I recall playing with
this stuff was under 4.3BSD or maybe SunOS 4.2.  Either way it was with a now-
ancient compiler and set of libraries, not one used today.  Now, thirty-odd
years later, I remember nothing much about it.  My apologies to you.
     Two questions occur to me.  Have you tried using gcc/g++ as a test?  Have
you tested it on a C program instead of a C++ program?

					Scott