pointer data structures don't overflow reliably, also this does not catch mmap error situations

[Christian Kellermann]

I have just came across this issue when dealing with a failed mmap FFI call. In this case mmap (The C function) will return a MAP_FAILED which is defined as (void*)-1 on linux and OpenBSD.

The mmap code checks for this by doing a (eq? -1 addr2). This is fine for 32 bit systems but not for 64 bit systems.

;; on 32 bit
#;2> (address->pointer -1)
#<pointer 0xffffffff>

;; on 64 bit
#;2> (address->pointer -1)
#<pointer 0x0>
#;3> (pointer->address #2)
1.84467440737096e+19

Note how the pointer printing code also gets it wrong.

A current workaround would be to explicitly check for the -1 pointer representation:

(pointer=? (address->pointer -1) addr2)

This works but looks icky. I am not sure how to handle this right.