Exceptions (was Re: How do I go about creating a minimal GNAT runtime?)

[anon@anon.org (anon)]

To compile and execute a simple program that uses a raise statement 
such as in the following code:

    --
    -- Sample code
    --
    procedure test is
      begin
        raise Program_Error ;
      end test ;

you will need the following list of packages in your "rts/adainclude" and 
the *.ali stored in "rts/adalib". You will also need to build the 
"libgnat.a" by using the "ar r <list of object files>" command and store 
in the "rts/adalib" dir.


a-except.adb  -- Ada.Exceptions            Edited to conform to RM.
a-except.ads                               Simpler design. That removes
                                           most Import/Exports except for
                                           exports for the RChecks 
                                           routines.
                                           Rchecks routines defined in 
                                           body and are rewritten to use 
                                           Raise_Exception instead of 
                                           GNAT's complex algorithm. 
                              

a-unccon.ads  -- Ada.Unchecked_Conversion
ada.ads       -- Ada

s-secsta.adb  -- System.Secondary_Stack    Compiler uses this package for 
s-secsta.ads                               functions that return a string 
                                           value. Also requires
                                           System.Storage_Elements.

s-memory.adb  -- System.Memory             This is a test environmental
s-memory.ads                               package that simulates a heap
                                           Needs a true hardware memory 
                                           management.  That can handle 
                                           static and virtual system.

s-stalib.adb  -- System.Standard_Library   Defines standard Exceptions
s-stalib.ads                               and storage. Basically copied 
                                           from GNAT. 

s-stoele.adb  -- System.Storage_Elements   
s-stoele.ads

system.ads    -- System                    GNAT compiler based.

--
-- Extra packages use for output of exception message
--

g-io.adb      -- GNAT.IO                   use for Put/Put_Line/New_Line
g-io.ads                                   connects to Video_IO

gnat.ads      -- GNAT

video_io.adb  -- Video_IO                  Text/Graphic SAGA device driver
video_io.ads                              



The reason you must rewrite "Ada.Exceptions" is that it uses multiple 
c-to-os functions, which some are defined in:

System.CRTL   -- defines C RTL ( not used in an Ada only OS )
System.Memory -- defines C memory functions. ( Needs be defined 
                 Ada to CPU Memory routines first )
              -- In other words a complete memory management system 
              -- is needs to make this package fully functional, but
              -- it can be simulate by using a large array of bytes.
              -- 
cio.c         -- defines C RTS to OS for I/O operations.  Must be 
              -- converted to a complete sub-system. In my example 
              -- I used a modified "GNAT.IO" and the "Video_IO" 
              -- device driver.

Then there the "System.Soft_Links" package. Do you really need 
it.  In most cases, for the core of the kernel the answer is No!


Now there are some binder variables are procedures that needs to be 
define in Ada, they are normally found in "Initialize.c", "init.c", 
"finalize.c". In my example I create a package called "gnat_library"
to store these in Ada routines and variables.
#
#
#
rm test
gnat compile  gnat_library.adb --RTS=rts
#
gnat compile  test.adb         --RTS=rts
gnat bind     test.ali         --RTS=rts
#
# To make the routine executable, must move the "function main" to 
# the beginning of the ada_main package before compiling.
#
gnat compile  b~test.adb       --RTS=rts -gnatA -gnatWb -gnatiw -gnatws
#
#  gnatlink test.ali gnat_library.o -n -v -v --RTS=rts
#
#  Problem: Adds all gcc libraries and includes host Ada Library Path 
#           and in some case will cause linker to stop processing. So 
#           it still better to use the "gcc" program.
#
gcc  b~test.o gnat_library.o ./test.o text_io.o video_io.o --RTS=rts       \
     -o test -L./ -L/example/ada/gnat/rts/adalib/                          \
     /example/ada/gnat/rts/adalib/libgnat.a
#
#
#


In <eb511600-6446-4bad-b859-0d7444416a4c@d36g2000prf.googlegroups.com>, Lucretia <lucretia9@lycos.co.uk> writes:
>Hi (again),
>
>It's been a while, but I'm coming back to my Ada kernel again. I've
>been messing with my helo_world_kernel which I built using no runtime
>(see http://www.archeia.com for more info).
>
>Having just spoken to Ludovic on #Ada, he pointed out that the gnat
>tools can use a basic cross tool set, like the ones I have built
>myself (again, see the above link). My toolset comprises of a gnat1
>compiler and a gnatbind for my targets. I found that it does work
>using the --GCC and --GNATBIND flags, and I need to make sure the
>cross tools and the host tools are of the same GCC version otherwise
>GNAT throws up ALI format errors.
>
>The thing is, I've been trying to enable exceptions, but keep coming
>across big problems in that the runtime requires features that are
>being restricted, such as returning aggregates and assigning
>composites, returning unconstrained objects which requires the
>secondary stack. So, what I really need to know is, how do I create a
>runtime which is restricted in this way for bare hw access?
>
>Thanks,
>Luke.