mallocPlainForeignPtrBytes -1000 gives runtime internal error: allocGroup: requested zero blocks

[andrewbirkett]

Passing negative numbers to mallocPlainForeignPtrBytes causes the following to appear:

Test: internal error: allocGroup: requested zero blocks
   (GHC version 6.10.4 for i386_unknown_linux)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
Aborted

Originally, a bug in my app meant that I called Data.ByteString?.hGet with a negative 'numBytes' argument, however I've managed to boil it down to a one line test case involving just mallocPlainForeignPtrBytes as follows:

$ cat Test.hs
import GHC.ForeignPtr (mallocPlainForeignPtrBytes)
main = mallocPlainForeignPtrBytes (-1000)

$ ghc --make Test.hs 
[1 of 1] Compiling Main             ( Test.hs, Test.o )
Linking Test ...

$ ./Test
Test: internal error: allocGroup: requested zero blocks
    (GHC version 6.10.4 for i386_unknown_linux)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
Aborted

The magnitude of the number appears to have some effect; with ghc 6.10.1 it seemed to reliably crash with numBytes <= -9. But when I upgraded to ghc 6.10.4, the test case started working. However, changing to -1000 reliably causes a crash on my box - perhaps the behaviour depends on heap layout. Either way, the function should probably behave more gracefully .. perhaps raising an exception.

Full gory details of my setup (ie. ghc -v output, gcc version) are attached because they messed up the formatting.

[andrewbirkett]

uname/gcc/ghc -v output

[duncan]

bytestring hGet is now fixed in the darcs repo. Also audited for other cases in the bytestring package.

Looking at the GHC.ForeignPtr? code, the following probably need fixing:

mallocForeignPtr
mallocForeignPtrBytes
mallocPlainForeignPtr
mallocPlainForeignPtrBytes

In the case of the non-"Bytes" versions that use Storable, that'd be a check for the Storable sizeOf function returning a negative value.

[simonmar]

Fixed (libraries/base):

Wed Nov 25 06:38:22 PST 2009  Simon Marlow <marlowsd@gmail.com>
  * check for size < 0 in mallocForeignPtrBytes and friends (#3514)

[igloo]

Merged