Re: GNAT and Memory Maps?

[Simon Wright <simon@pushface.org>]

Freejack <Freejack@nomail.com> writes:

> I've been picking through the GNAT docs (and Ada docs in general) in
> an attempt to figure out how/if and when/why the Ada compiler might
> choose to use an mmap system call in deference to a malloc/calloc or
> alloca call.

I would be very surprised if GNAT ever chose to use mmap -- how would
it know which file to map?

> Basically, I'm doing some low level routines and I need explicit
> control over what pages are swapped and when. ( mmap() mlock()
> munlock() and munmap() are the usual C functions for handling this.)

These functions are (C bindings to) system calls; so at some point
there is going to be a software interrupt (int-something on Intel). I
don't see what advantage you'll get by rewriting the C bindings?

> I'm using Linux at the moment, and I could just as easily use the
> native C library (glibc). However, I want to handle this entirely in
> Ada. I'm using the No_Run_Time Pragma.

I suspect you can still link against the C libraries with No_Run_Time.


Someone suggested use of a storage pool, but (a) I doubt that's
compatible with No_Run_Time, (b) storage pools are about supporting
multiple allocations, if you want to "mmap these 16#40000# bytes which
I will treat as a data structure like _that_" storage pools seem
irrelevant.