ANNOUNCE: MonadCatchIO-foreign

Simon Marlow marlowsd at
Mon Jun 7 11:30:54 EDT 2010

On 03/06/2010 07:29, Evan Laforge wrote:
> On Sun, May 30, 2010 at 5:15 PM, Antoine Latter<aslatter at>  wrote:
>> Hi GHC,
>> Is there a reason that Foreign.Marshall.Array.allocaArray calls into
>> allocaBytes instead of allocaBytesAligned? Since alloca needs the
>> alignment, wouldn't allocaArray also need it?
>> I'm not too up on how memory access is supposed to work, it was just
>> something that jump out at me.
> I've been waiting for a response on this, because I'm curious too, in
> fact I always have been.  At the upgrade to 6.10, ghc suddenly started
> using 'alignment' and all my programs which had defined it to
> 'undefined' since I didn't know what alignment was for and it didn't
> seem to be used, started crashing.  So I dug around, dug up the '#let
> alignment' macro boilerplate, and copy and pasted it around.
> However, at the same time, my program started rarely but consistently
> crashing with an assertion failure from the gc runtime.  I'm
> suspicious of the inconsistent use of alignment, but it's hard to use
> allocaBytesAligned since it's not exported, and the ffi lib is part of
> ghc and it's not obvious how to modify it.

Here's the ticket:

Lennart's patch added allocaBytesAligned to Foreign.Marshal.Alloc, but 
we'll have to do a library proposal to add that.

If you can reproduce the assertion failure, please submit a bug report.


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