= FpDebug

link:https://www.gnu.org/licenses/gpl-2.0.html[image:https://img.shields.io/badge/license-GPL2-blue.svg[GNU General Public License, version 2]]

FpDebug is a heavyweight Valgrind tool for detecting floating-point accuracy problems.

The tool uses MPFR for its side-by-side computation in higher precision. Because MPFR is run with the tool on top of Valgrind, it has only access to the partial C library provided by Valgrind. Thus, a patch for MPFR is provided that adjusts it to run on top of Valgrind. As GMP is used by MFPR, a patch for GMP is also provided.

== Origin

This project was started during my Bachelor's thesis (winter 2010/11). The results have been published in:

link:http://dl.acm.org/citation.cfm?id=2254118[A Dynamic Program Analysis to find Floating-Point Accuracy Problems] link:https://www.fbenz.net/static/pldi12_benz.pdf[[PDF]] + link:https://www.fbenz.net/[Florian Benz], link:https://www.bio.informatik.uni-mainz.de/andreas-hildebrandt/[Andreas Hildebrandt], and link:http://compilers.cs.uni-saarland.de/people/hack/[Sebastian Hack] + PLDI '12: Proceedings of the 2012 ACM SIGPLAN Conference on Programming Language Design and Implementation

== Quick start

The docker folder contains Dockfiles for several systems that can be used to build and play around. During the build a small example program is also built and analyzed to check that everything works.

[source,bash] .Build and run Docker image

sudo docker build -t fpdebug . sudo docker run -it fpdebug /bin/bash

== Build from source

NOTE: The version on master runs with Valgrind 3.7 and might not work on more recent systems than Ubuntu 12.04. However, a version for Valgrind 3.12 can be found here: https://github.com/fbenz/FpDebug/pull/2 . But so far it has only been tested on small examples. Tests have been performed on Ubuntu 16.04 and Ubuntu 16.10.

NOTE: Only 64bit systems are supported.

The following installation instructions are for Ubuntu 12.04.5 LTS (64bit). The instructions should be similar for most other Linux systems.

[source,bash] .Install build dependencies

Git is only needed to check out the sources

sudo apt-get install git

m4 is a dependency of GMP

sudo apt-get install m4

libc6-dbg is required for Valgrind (otherwise it fails at runtime)

sudo apt-get install libc6-dbg

[source,bash] .Get the sources

git clone [email protected]:fbenz/FpDebug.git

[source,bash] .Install patched GMP 5.0.1

./install_gmp.sh

[source,bash] .Install patched MPFR 3.0.0

./install_mpfr.sh

[source,bash] .Install Valgrind with FpDebug

./install_valgrind.sh

== Running FpDebug

[source,bash] .Build an example

cd valgrind/fpdebug/examples gcc test_1.c -O0 -g -o test_1.out (or $ gcc test_1.c -O0 -g -mfpmath=387 -o test_1.out )

[source,bash] .Run FpDebug

./valgrind/install/bin/valgrind --tool=fpdebug valgrind/fpdebug/examples/test_1.out

[source,bash] .FpDebug output

==7041== FpDebug-0.1, Floating-point arithmetic debugger ==7041== Copyright (C) 2010-2011 by Florian Benz. ==7041== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info ==7041== Command: valgrind/fpdebug/examples/test_1.out ==7041== ==7041== precision=120 ==7041== mean-error=yes ==7041== ignore-libraries=no ==7041== ignore-accurate=yes ==7041== sim-original=no ==7041== analyze-all=yes ==7041== bad-cancellations=yes ==7041== ignore-end=no Test program: machine epsilon, client request Sum: 1.0000000e+00 Running on valgrind ==7041== (float) sum PRINT ERROR OF: 0x7FF0000F4 ==7041== (float) sum ORIGINAL: 1.00000000000000 * 10^0, 1/120 bit ==7041== (float) sum SHADOW VALUE: 1.00000025000000 * 10^0, 49/120 bit ==7041== (float) sum ABSOLUTE ERROR: 2.50000002921524 * 10^-7, 27/120 bit ==7041== (float) sum RELATIVE ERROR: 2.49999940421539 * 10^-7, 120/120 bit ==7041== (float) sum CANCELED BITS: 0 ==7041== (float) sum Last operation: 0x4007AD: main (test_1.c:14) ==7041== (float) sum Operation count (max path): 5 ==7041== DUMP GRAPH (test_1_sum.vcg): successful ==7041== ==7041== DUMP GRAPH (valgrind/fpdebug/examples/test_1.out_1_0.vcg): successful ==7041== SHADOW VALUES (valgrind/fpdebug/examples/test_1.out_shadow_values_relative_error_1): successful ==7041== SHADOW VALUES (valgrind/fpdebug/examples/test_1.out_shadow_values_canceled_1): successful ==7041== SHADOW VALUES (valgrind/fpdebug/examples/test_1.out_shadow_values_special_1): successful ==7041== MEAN ERRORS (valgrind/fpdebug/examples/test_1.out_mean_errors_addr_1): successful ==7041== MEAN ERRORS (valgrind/fpdebug/examples/test_1.out_mean_errors_canceled_1): successful ==7041== MEAN ERRORS (valgrind/fpdebug/examples/test_1.out_mean_errors_intro_1): successful

=== License

FpDebug is Open Source software released under the link:https://www.gnu.org/licenses/gpl-2.0.html[GNU General Public License, version 2].