RE: [Valgrind-users] Uninitialised values

[Stephane D. <ste...@ex...>]

Yes, the random data came from the RSA_public_encrypt function of the
openssl package.

Thanks for the explanation


On Tue, 2003-06-24 at 17:34, Lee Dilkie wrote:
> Did your random data come from, say, the openssl random function? Or
> something similar? The root cause would be that those functions xor in
> random data into the buffer without first initializing it. Doing so is good
> for random-ness (adds some entropy) but valgrind keeps track that the memory
> was never "properly" written (and xor onto itself doesn't fool valgrind) so
> it gets reported. you can get rid of the valgrind message by initializing
> your buffer before calling the rand functions.
> 
> 
> -lee
> 
> > -----Original Message-----
> > From: val...@li...
> > [mailto:val...@li...]On Behalf
> > Of Vincent
> > Penquerc'h
> > Sent: Tuesday, June 24, 2003 6:17 AM
> > To: 'Stephane Donze'; val...@li...
> > Subject: RE: [Valgrind-users] Uninitialised values
> >
> >
> > > This function does a lot of left shifts, right shifts and other
> > > bit-level stuff. Is it possible that my data accidentally
> > contains the
> > > bit pattern used by valgrind to trace uninitialised data ?
> >
> > AFAIK, Valgrind doesn't rely on any pattern in the actual data to
> > detect uninitialized data, especially as it can detect this at the
> > bit level (you'd have to choose either 0 or 1 to mean "uninitialized"
> > for a bit, which makes it hard to avoid the pattern :))
> >
> > Valgrind maintains separate validity/addressability bits, but that
> > is outside your program, so you don't see it.
> > It's possible that Valgrind gets confused, if some insn wrongly
> > sets/checks validity flags. Or, maybe you are encoding more than
> > the actual data ? Or do you mean random data, as initialized via
> > a pseudo random number generator, or as whatever happened to lie
> > in memory at the time (in which case you will get undefinedness) ?
> >
> > --
> > Vincent Penquerc'h
> >
> >
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