Profiling C application
ml at netfence.it
Fri Apr 2 08:16:12 UTC 2021
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:
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:
libarchive.so.13 => /usr/local/lib/libarchive.so.13 (0x8004a0000)
libboost_system.so.1.72.0 => /usr/local/lib/libboost_system.so.1.72.0
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.
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"?
bye & Thanks
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