[Haskell-cafe] Strange results when trying to create large Bool arrays.

[Bryan O'Sullivan]

Ketil Malde wrote:

> I'd really like to have errors on overflow, at least as an option, even
> if it is costly in terms of performance.  Is there a Trac ticket or
> something for this?

Not that I know of.  I filed a Trac ticket against ByteString's readInt 
function before I noticed that read has the same problem, and it was 
closed because read does the same thing.  I've been reluctant to pop my 
head over the parapet since.

CPUs generally don't trap on integer overflow, so generating the 
additional tests and jumps necessary to handle this would be a bit 
involved, and would certainly cost a few percent in performance. 
There's also overflow in truncation and sign conversions to worry about, 
e.g. Word32 -> Word16, Word32 -> Int (on 32-bit systems), etc.

On the other hand, integer overflows have long been a popular attack 
vector for getting programs to misbehave in the exploit community.  If 
you Google for "ia32 integer overflow" or "i386 integer overflow", the 
first several *pages* of results in each case consist entirely of 
security advisories.  Haskell's FFI makes it as vulnerable as the 
libraries it interfaces to.

Here's a cute-looking paper entitled "Efficient and accurate detection 
of integer-based attacks".

http://www.cs.cmu.edu/~dbrumley/pubs/integer-ndss-07.pdf

	<b