Re: cse.c bug

[Thomas Koenig <ig25 at mvmap66 dot ciw dot uni-karlsruhe dot de>]

I wrote:

>[Did I mention that playing around with Checker is fun? :-]

Before I get more E-Mails asking what Checker is, here is its
description from the Linux GNU/Debian package:

# Drop-in addition to `gcc' that allows programmers to find most
# memory-related bugs easily.  Checker automatically finds:
# .
#     * null pointer dereferences (read, write, and execute accesses)
#     * writes to read-only memory
#     * accesses to free blocks (read, write, and execute)
#     * reads/writes to uninitialized bytes (in automatic and dynamic memory)
#     * reads/writes to "red zones" (in automatic and dynamic memory)
#     * reads/writes/executes outside memory segments
#     * free called with address not obtained from malloc
#     * free an already freed block
#     * ...and many more!
# .
# Checker's main disadvantage is that it causes the program to run many
# times slower.  You can compile your program to use Checker by using
# the command `checkergcc' in place of `gcc'.

Checker does this by manipulating the output of the assembler.  Each
assembler instruction is replaced by a sequence of instructions which
checks all these things.  Of course, this is highly machine-dependend,
causes enormous code bloat and makes the code slooooow.

Checker so far is only available for i386-linux and sparc-linux (AFAIK).
The only version which really works is the one for Debian hamm
(unstable).  It includes glibc2.0.5 and a few other goodies, and is
based on gcc 2.7.2.3.  It has found quite a number of bugs in my
programs, and at least four bugs in glibc (or so I'm told :-).  If you
run Linux/386 with glibc 2.0.5, try to get this version from
ftp://ftp.debian.org/pub/linux/debian/hamm/hamm/binary-i386/devel/checker_0.8-18.deb
If you don't have dpkg installed, you can unpack a *.deb file it with
"ar x foo.deb ; tar -xvzf data.tar.gz"

The tests I've run on egcs were done with the first-stage compiler,
with "CC=checkergcc configure".
-- 
Thomas Koenig, Thomas.Koenig@ciw.uni-karlsruhe.de, ig25@dkauni2.bitnet.
The joy of engineering is to find a straight line on a double
logarithmic diagram.