Re: Valgrind updates

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Jan 29, 2009, 14:54 UTC
Message-ID: <alpine.DEB.1.00.0901291547510.3586@pacific.mpi-cbg.de>
In-Reply-To: <alpine.DEB.1.00.0901291510520.3586@pacific.mpi-cbg.de>

Hi,

On Thu, 29 Jan 2009, Johannes Schindelin wrote:

Show 25 quoted lines

> On Wed, 28 Jan 2009, Mark Adler wrote:
> 
> > On Jan 28, 2009, at 3:27 PM, Johannes Schindelin wrote:
> > >On Wed, 28 Jan 2009, Mark Adler wrote:
> > > >2.  Can someone send me the input and the 58 bytes of output from this
> > > >  case?
> > >
> > >I did better than that already...
> > >http://article.gmane.org/gmane.comp.version-control.git/107391
> > 
> > Johannes,
> > 
> > Thanks for the input and code.  When I run it, the byte in question at 
> > offset 51 is 0x2c.  The output decompresses fine and the result matches 
> > the input. If I change the 0x2c to anything else, decompression fails.  
> > The 58 bytes are below.
> > 
> > Can you also send me the 58 bytes of output that you get when you run it?
> 
> I get exactly the same 58 bytes.  Together with the fact that the 52nd 
> byte is actually required to be 0x2c, I think that maybe valgrind is 
> having problems to track that this byte was correctly initialized.
> 
> BTW did you have any chance to test the code with valgrind on your 
> machine?  It might be related to this here platform (x86_64).

Now, things get interesting.

Of course, I made sure that I had the newest zlib installed before mentioning publically that I found a strange valgrind issue.

But I did not build it from source myself; I installed what Ubuntu Gutsy Gibbon had to offer me.

Now that I tried to investigate further by compiling zlib from source, instrumenting it with various valgrind-specific code to find out what is actually happening, I cannot reproduce anymore!

So I searched for the sources that Ubuntu provides, and I _still_ cannot reproduce.

So I'll just go for the easy solution, install plain straightforward zlib-1.2.3 (as opposed to zlib_1.2.3.3.dfsg-12ubuntu1), and apologise to y'all for all the bruhaha.

Ciao, Dscho

P.S.: Note that there is still something fishy going on, as Ubuntu's zlib generates the deflated stream correctly. But that will have to be investigated by someone with substantially more time on her hands than me.