Question

In the Haskell FFI, what is the essential difference between arrays allocated with withArray and newArray? I have function in c that works with newArray but segfaults with withArray. The working code looks bit like this:

a <- newArray items
fficall a
free a

The code that segfaults looks like this:

withArray items fficall

The segfault happens up when the ffi enters a blas function. Since I’m not allowed to show the c-code, the question is, “please show me an example c-function that also segfaults with withArray but not with newArray.”

Answer 1

From what I can see, newArray ends up calling malloc to do the allocation, while withArray calls allocaArray, which ends up in newAlignedPinnedByteArray#.

Perhaps your function is relying on the memory being allocated by malloc, for example by attempting to realloc or free it?