haskell2:
David Brown wrote:
Ian Lynagh wrote:
On Mon, Mar 05, 2007 at 10:51:46AM -0800, David Brown wrote:
My program 'harchive' http://www.davidb.org/darcs/harchive/ breaks if compiled with '-O'. Just wondering if anyone has suggestions on how to figure out what might be causing this. What do you mean by "breaks"?
I'm now rebuilding individual parts with -O to see if I can isolate the problem(s).
Well, that helped. I found the problem. I had something like:
import qualified Data.ByteString as B
let hash = B.pack $ replicate (#const SHA_DIGEST_LENGTH) 0 ... B.useAsCStringLen hash $ \ (hdata, _) -> do c_sha1Final hash ctx return hash
But this seems to be causing the hash to be garbage, and possibly have c_sha1Final write a 20-byte hash into some garbled piece of memory.
Ireplaced this with
let hashLen = (#const SHA_DIGEST_LENGTH) hashData <- mallocForeignPtrBytes hashLen withForeignPtr hashData $ \hashP -> do c_sha1Final hashP ctx B.copyCStringLen (hashP, hashLen)
and the code works both with and without optimization.
Dave
Ah, this is my fault! The old api used 'useAsCSTringLen' unsafely. Its a zero-copying version. The default is now copyCStringLen. See this thread for the issues involved: http://www.haskell.org/pipermail/libraries/2007-January/006783.html and for how it has been resolved: http://www.haskell.org/pipermail/libraries/2007-January/006801.html So yes, using 'copyCStringlen' is the appropriate thing to do, if you don't want to guarantee the C side of things. -- Don