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Document profiling option 

Add instructions on building cprover binaries so they can be profiled
by a tool like gprof.
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Owen 2019-08-22 10:26:57 +01:00 committed by Owen
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doc/architectural/compilation-and-development.md
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@ -270,3 +270,35 @@ branch, e.g. to run it on lines that have been changed from `develop`:
There are also instructions for adding this as a git pre-commit hook in
[CODING_STANDARD.md](https://github.com/diffblue/cbmc/blob/develop/CODING_STANDARD.md#pre-commit-hook-to-run-cpplint-locally).
\section compilation-and-development-section-time-profiling Time profiling
To do time profiling with a tool like `gprof`, the flags `-g` (build with debug
symbols) and `-pg` (enable profiling information) must be
used when compiling, and `-pg` must be used when linking. If you are building
with cmake you can just add "-Denable_profiling=1" to your cmake invocation, and
reload cmake before building your desired binary. Note that these flags require
everything to be rebuilt, so it will take a long time even if you are using
ccache.
Run your binary as normal. A file called gmon.out will be created in the
working directory of the binary at the end of execution. In most instances this
will be the same as the working directory at the beginning of execution. It is
also possible to choose the output location by setting the environment variable
GMON_OUT_PREFIX - the output file location is then whatever you set it to with
the process id appended to the end.
Make sure gprof is installed by running `gprof -v`. If it is not installed then
run `sudo apt install binutils`.
Run `gprof <path-to-binary> <path-to-gmon.out>` and redirect the output to a
file. This will take a while to run - e.g. 12 minutes for test-gen run on a
trivial function.
The output file will now be a large text file. There are two sections: the "flat
profile", which ignores context, and just tells you how much time was spent in
each function; and the "call graph", which includes context, and tells you how
much time was spent within each call stack. For more information see online
tutorials, like
https://ftp.gnu.org/old-gnu/Manuals/gprof-2.9.1/html_chapter/gprof_5.html