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From: Francesco PIRANEO GIULIANO <liste.fpiraneo@gmail.com>
Newsgroups: comp.lang.ada
Subject: Does mmap gives a right result?!
Date: Sun, 3 Oct 2010 04:27:25 -0700 (PDT)
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Date: 2010-10-03T04:27:25-07:00
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Hi all,

always trying to handle linux framebuffer with ada; big goal reached
yesterday accessing fixed and variable data structures importing and
executing ioctl functions.

Now I have to draw inside the framebuffer and I've imported mmap as
follows:

   function mmap(addr : in u32; length : in u32; prot : in mmap_prot;
flags : in mmap_flag; fd : in file_id; offset : in u32) return
Void_Ptr;
   pragma import( C, mmap, "mmap" );
   pragma import_function(mmap);

Void_Ptr is defined as follows:

   type void is mod System.Memory_Size;
   for void'Size use System.Word_Size;

   type Void_Ptr is access all Void;
   pragma Convention (C, Void_Ptr);

The lines above has been derived by:
http://en.wikibooks.org/wiki/Ada_Programming/Types/access#Where_is_void.2A.3F

Finally, the mmap has been called as follows:

      fbindex := mmap(0, fbhandler.fixinfo.smem_len,
fbhandler.PROT_READ + fbhandler.PROT_WRITE, fbhandler.MAP_FILE +
fbhandler.MAP_SHARED, fbid, 0);

NOTE: I defined PROT_READ and so on as constants in my code;

First question: I have to analyze if fbindex is /= -1 otherwise I have
to raise an exception:

      if integer(fbindex) = -1 then
	     raise BADMMAPRESULT;
      end if;

...seems to be the most logical comparision BUT the following error in
compile phase appears: "illegal operand for numeric conversion" -- Any
help is really apreciated here! :-)

When commenting out the above instructions and starting the compiled
application, everything goes right except, when I try to draw inside
the first location the program hungs with the following:

raised STORAGE_ERROR : stack overflow (or erroneous memory access)

I'm quite sure my mmap doesn't run properly. I'm about to makes all
framebuffer's interfacing functions in C then implement the remaining
in Ada but it will be a nice things if everything can be made with the
same language.

Any clues or opinion is welcome about.

Francesco