mirror of
https://github.com/Zenithsiz/ftmemsim-valgrind.git
synced 2026-02-03 18:13:01 +00:00
ec8e145850
medium resolution (4 callers) used to compare errors.
To look at the strange side effect, do:
./vg-in-place -v --suppressions=memcheck/tests/suppfreecollision.supp memcheck/tests/suppfree activatenondangerouserror
You obtain at the end:
...
--19240-- used_suppression: 2 suppressnondangerouserror memcheck/tests/suppfreecollision.supp:2
...
showing that the suppression aiming at suppressing a nondangerous error has in fact
suppressed more than expected.
This is because m_errormgr.c compares the exe_context in medium resolution/4 calls
(or low resolution/2 calls once 100 errors have been collected).
The error machinery first encounters the non dangerous error. This error is suppressed,
because all callers match the suppression entry. In particular, we have
in the stacktrace the function ok_to_suppress_double_free_from_this_fun
Then the error machinery encounters the second error.
The stacktrace of the 2nd error has the same first 4 callers than the non
dangerous error. So the 2nd error is considered equal to the first one
and is (unexpectedly in my opinion) suppressed.
This looks a bug (or at least something very surprising).
(the doc mentions the fact that errors are 'commoned up' on 4 callers, but
I am not sure the above side effect was understood).
There are several ways this can be improved, some are more easier than other
* have --error-resolution=low/med/high
similar to the memcheck --leak-resolution=low/med/high
(which default value would we take for this new clo ?)
* have a lot more intelligent error comparison:
when comparing an error with a suppressed error, one must
check that the callers used for suppression are equal.
This looks difficult to implement and probably a significant slow down
in the error machinery, which will impact applications producing
many suppressed errors (e.g. helgrind + some pthread lib errors).
This also implies more memory (e.g. one byte per caller in the
error, to indicate which caller(s) were used to suppress.
Still wondering what to do with * and ... ?
* have a somewhat more intelligent error comparison:
Instead of comparing only the callers used for suppression, we
compare the range first..last caller used (so including some
callers in the range that were not used to suppressed if e.g.
a ... matching was put in the supp entry).
Probably still a slowdown (less than previous solution ?)
and less memory than the previous solution.
But also not completely clear how to compute the range.
* always re-evaluate the suppression : this will very probably be
a significant slow down.
* do nothing, as nobody complained about this behaviour up to now :)
* ??? any other idea
git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13914
Release notes for Valgrind
~~~~~~~~~~~~~~~~~~~~~~~~~~
If you are building a binary package of Valgrind for distribution,
please read README_PACKAGERS. It contains some important information.
If you are developing Valgrind, please read README_DEVELOPERS. It contains
some useful information.
For instructions on how to build/install, see the end of this file.
If you have problems, consult the FAQ to see if there are workarounds.
Executive Summary
~~~~~~~~~~~~~~~~~
Valgrind is a framework for building dynamic analysis tools. There are
Valgrind tools that can automatically detect many memory management
and threading bugs, and profile your programs in detail. You can also
use Valgrind to build new tools.
The Valgrind distribution currently includes six production-quality
tools: a memory error detector, two thread error detectors, a cache
and branch-prediction profiler, a call-graph generating cache abd
branch-prediction profiler, and a heap profiler. It also includes
three experimental tools: a heap/stack/global array overrun detector,
a different kind of heap profiler, and a SimPoint basic block vector
generator.
Valgrind is closely tied to details of the CPU, operating system and to
a lesser extent, compiler and basic C libraries. This makes it difficult
to make it portable. Nonetheless, it is available for the following
platforms:
- X86/Linux
- AMD64/Linux
- PPC32/Linux
- PPC64/Linux
- ARM/Linux
- x86/MacOSX
- AMD64/MacOSX
- S390X/Linux
- MIPS32/Linux
- MIPS64/Linux
Note that AMD64 is just another name for x86_64, and Valgrind runs fine
on Intel processors. Also note that the core of MacOSX is called
"Darwin" and this name is used sometimes.
Valgrind is licensed under the GNU General Public License, version 2.
Read the file COPYING in the source distribution for details.
However: if you contribute code, you need to make it available as GPL
version 2 or later, and not 2-only.
Documentation
~~~~~~~~~~~~~
A comprehensive user guide is supplied. Point your browser at
$PREFIX/share/doc/valgrind/manual.html, where $PREFIX is whatever you
specified with --prefix= when building.
Building and installing it
~~~~~~~~~~~~~~~~~~~~~~~~~~
To install from the Subversion repository :
0. Check out the code from SVN, following the instructions at
http://www.valgrind.org/downloads/repository.html.
1. cd into the source directory.
2. Run ./autogen.sh to setup the environment (you need the standard
autoconf tools to do so).
3. Continue with the following instructions...
To install from a tar.bz2 distribution:
4. Run ./configure, with some options if you wish. The only interesting
one is the usual --prefix=/where/you/want/it/installed.
5. Run "make".
6. Run "make install", possibly as root if the destination permissions
require that.
7. See if it works. Try "valgrind ls -l". Either this works, or it
bombs out with some complaint. In that case, please let us know
(see www.valgrind.org).
Important! Do not move the valgrind installation into a place
different from that specified by --prefix at build time. This will
cause things to break in subtle ways, mostly when Valgrind handles
fork/exec calls.
The Valgrind Developers