Ada Bare Bones: Difference between revisions

The following code demonstrates setting up a directory structure for the RTS:

 

mkdir -p bare_bones/src/pc

cd bare_bones

mkdir -p rts/src

mkdir -p obj

 

The best way to begin creating a new run-time library is to base it upon the existing source files obtained from the system GNAT installation, modifying them where necessary.

The following code demonstrates copying the required files from the host system's GNAT installation's run-time library into <tt>rts/src</tt> and then creating symbolic links to <tt>rts/boards/${arch}/adainclude</tt>. Where <tt>${arch}</tt> is <tt>i386</tt>, <tt>armv6</tt>, etc. The source location will need to be modified to reflect the location of the system compiler.

 

system_compiler_dir="/usr/lib/gcc/x86_64-linux-gnu/8"

rts_dir="${PWD}/rts"

ln -s "${rts_dir}/src/$f" "${rts_dir}/rts/boards/i386/adainclude/$f"

done

 

==Files==

Additionally, it is possible to apply additional global configuration files by appending the following line to the <tt>Builder</tt> package in a GNAT project file:

 

package Builder is

-- ...

for Global_Configuration_Pragmas use "kernel.adc";

end Builder;

 

It is also possible to instruct the compiler to apply additional files containing configuration pragmas to the current compilation using the switch <tt>-gnatec=path</tt> on the command line. These configuration pragmas are applied in addition to those found in <tt>gnat.adc</tt>, if it is present.

See below for a list of restriction pragmas useful for a bare bones kernel and runtime:

 

pragma Discard_Names;

pragma Restrictions (No_Enumeration_Maps);

pragma Restrictions (No_Implicit_Dynamic_Code);

pragma Restrictions (No_Secondary_Stack);

 

'''Note:''' ''Do not use <tt>pragma No_Run_Time</tt>. It is obsolete.''

| Discard_Names || The Ada compiler automatically generates strings containing the names of enumerated data types, among others. These strings can be used in I/O.

 

type Fruit is (Orange, Banana, Apple);

-- Ada defines the following strings, "Orange", "Banana" and "Apple" in an array.

Put (Fruit'Image (Orange));

-- Prints "Orange" to the console.

 

This directive instructs the compiler not to generate these strings.

 

Passing the <tt>-r</tt> flag to the binder instructs it to emit a list of further restrictions that are possible to apply to the project.

package Binder is

for Default_Switches ("Ada") use ("-r");

end Binder;

 

===system.ads===

Also, add the following line in the private part of the package:

 

private

 

Run_Time_Name : constant String := "Bare Bones Run Time";

 

According to targparm.ads, it must be the first thing after the private keyword. It should also show up in error messages in parentheses, but I've not managed to get it to show up thus far. This is useful as it should show you which RTS you are currently using, just in case you configure your build incorrectly.

====last_chance_handler.ads====

 

with System;

 

(Source_Location : System.Address; Line : Integer);

pragma Export (C, Last_Chance_Handler, "__gnat_last_chance_handler");

 

====last_chance_handler.adb====

 

procedure Last_Chance_Handler

(Source_Location : System.Address; Line : Integer) is

end loop;

end Last_Chance_Handler;

 

The contents of the <tt>Last_Chance_Handler</tt> procedure will need to be tailored to the specific platform of the kernel. Typically this procedure will dump information regarding the exception to output media such as a [[Serial_Ports|serial port]].

Create a file called <tt>gnat.gpr</tt> in the root directory with the following contents:

 

library project gnat is

type Arch_Name is ("i386", "arm");

for Library_Dir use "rts/boards/" & Arch & "/adalib";

end gnat;

 

Now compile with the following command:

 

gprbuild -XBoard=pc -Pgnat.gpr

 

Inside <tt>rts/boards/i386/adainclude/</tt> the RTS sources should be symbolically linked along with the custom <tt>last_chance_hander</tt> and system files. Inside <tt>rts/boards/i386/adalib/</tt> there should be the <tt>libgnat-4.6.a</tt> file as well as <tt>*.ali</tt> matching the source files, which are required by GNAT.

====console.ads====

 

with System;

 

procedure Clear (Background : in Background_Colour := Black);

end Console;

 

====console.adb====

 

package body Console is

procedure Put

end Clear;

end Console;

 

===bare_bones.adb===

This is platform independent and therefore goes into the src directory.

 

with Console; use Console;

 

end Bare_Bones;

pragma No_Return (Bare_Bones);

 

===linker.ld===

Place this file in the root directory.

 

ARCH = i386

RTS_DIR = `pwd`/rts/boards/$(ARCH)

clean:

-rm obj/* *~ bare_bones

 

===bare_bones.gpr===

Place this file in the root directory.

 

project Bare_Bones is

type Arch_Name is ("i386", "arm");

end Linker;

end Bare_Bones;

 

==Raspberry Pi==

 

 

git clone git://github.com/gonzoua/u-boot-pi.git

 

cd u-boot-pi

make rpi_b_config

 

==Testing==

Make sure you have built the RTS above before this next stage otherwise you won't be able to compile the kernel.

 

make qemu

 

On the QEMU window, it should clear the screen, the the cursor won't move so it will be in the middle of the screen, in the top-left corner will be the message "Hello, bare bones in Ada."