Re: How to configure GNAT GPL on x86-64 Linux for ARM ELF development

[Adam Jensen <hanzer@riseup.net>]

I am trying the "Digital Output" example described here:
<http://www.inspirel.com/articles/Ada_On_Cortex_Digital_Output.html>

Compilation seems to be successful with these commands: 
gprbuild -c -u -f utils.adb --target=arm-eabi --RTS=zfp-stm32f4
gprbuild -c -u -f pins.adb --target=arm-eabi --RTS=zfp-stm32f4
gprbuild -c -u -f program.adb --target=arm-eabi --RTS=zfp-stm32f4

But linking fails like this:
arm-eabi-ld -T ../flash.ld -o program.elf program.o pins.o utils.o
pins.o: In function `pins__enable_output':
pins.adb:(.text+0x20): undefined reference to `__gnat_last_chance_handler'
pins.o: In function `pins__write':
pins.adb:(.text+0x7a): undefined reference to `__gnat_last_chance_handler'

The symbols in "pins" are:
arm-eabi-nm pins.o
         U __gnat_last_chance_handler
         U GPIOA_BSRR
         U GPIOA_MODER
00000000 D pins_E
00000000 T pins__enable_output
00000060 T pins__write
         U RCC_AHB1ENR

Eager to move forward, I cobbled together a GPR project file targeting 
the full Ravenscar profile.

#ravenScar.gpr
 project Ravenscar is
    for Source_Dirs use ("src");
    for Ignore_Source_Sub_Dirs use (".svn");
    for Object_Dir use "obj";
    for Exec_Dir use ".";
    for Main use ("program.adb");
    for Runtime ("Ada") use "ravenscar-full-stm32f4";
    for Target use "arm-eabi";

    package Builder is
        for Executable_Suffix use "";
        for Global_Configuration_Pragmas use "src/gnat.adc";
    end Builder;

    package Compiler is
        for Default_Switches ("ada") use ("-O0", "-gnatwa", "-gnatQ", "-
gnatw.X");
    end Compiler;

    package Binder is
        for Required_Switches ("Ada") use Binder'Required_Switches 
("Ada") &
            ("gnatbind_prefix=arm-eabi-") &
            ("--RTS=/home/hanzer/.local/gnat-arm/arm-eabi/lib/gnat/
ravenscar-full-stm32f4/") &
            ("-nostdlib");
        for Driver ("Ada") use
            "/home/hanzer/.local/gnat-arm/libexec/gprbuild/gprbind";
    end Binder;

    package Linker is
        for Driver use Compiler'Driver ("Ada");
        for Map_File_Option use "-Wl,-Map,";
        for Response_File_Format use "GCC_GNU";
        for Max_Command_Line_Length use "8192";
        for Required_Switches use Linker'Required_Switches &
            ("-L/home/hanzer/.local/gnat-arm/arm-eabi/lib/gnat/ravenscar-
full-stm32f4/adalib",
            "-nostartfiles", "-lgnat", "-lc", "-lgnat", "-lgcc",
            "-L/home/hanzer/.local/gnat-arm/arm-eabi/lib/gnat/ravenscar-
full-stm32f4/ld",
            "-T", "flash.ld");
    end Linker;
end Ravenscar;
-------------------------------------------------------------------------

I didn't really expect it to work - I am well into the realm of wild-ass 
guesses at this point. This is what happens:

gprbuild -P ./ravenscar.gpr
Compile
   [Ada]          program.adb
   [Ada]          pins.adb
   [Ada]          utils.adb
   [Ada]          registers.ads
Bind
   [gprbind]      program.bexch
   [Ada]          program.ali
program.adb:1: Program cannot be used as a main program
gprbind: invocation of gnatbind failed
gprbuild: unable to bind program.adb


On Wed, 23 May 2018 09:07:51 +0100, Simon Wright wrote:

> I think that the reason why the tutorial works and your attempt doesn't
> is that the tutorial was developed on a Raspberry Pi, which is already
> an ARM-based machine, so the native compiler actually has a runtime
> (i.e. system.ads etc etc) visible to it.

This is so very relevant yet the tutorial seems rather vague [to me] on 
this point. It should be explicit, in bold, in a highlighted box on the 
front page, IMO. Thanks again for pointing that out. Even on a second 
reading, it isn't clear [to me] that using a Raspberry Pi as a software 
development platform is the environment of the tutorial. 

<http://www.inspirel.com/articles/
Ada_On_Cortex_Documentation_And_Tools.html>

> but a simpler (more memorable!) procedure might be to construct your
> own:
> 
> 1. Create directories adainclude/, adalib/
> 
> 2. Copy $prefix/arm-eabi/lib/gnat/zfp-stm32f4/gnat/system.ads to your
>    adainclude/ ($prefix is the root of your compiler installation, I
>    think ~/.local/gnat-arm)
> 
> The zfp- (zero footprint) runtime is the closest to what you need, and
> the fact that the -stm32f4 part isn't quite right shouldn't matter; I
> suspect that system.ads is the same for all the zfp runtimes.
> 
> Now,
> 
>    $ arm-eabi-gcc --RTS=. -c program.adb

I will try this next. It's a bit like learning to swim by jumping into 
the deep end of the pool (or being thrown in). This article might help:

"Porting the Ada runtime to a new ARM board"
<https://blog.adacore.com/porting-the-ada-runtime-to-a-new-arm-board>

I also ordered a copy of this book (below) since I don't actually know 
the Ada programming language (I have plenty of experience with VHDL).

<https://www.amazon.com/Programming-Ada-2012-John-Barnes/dp/110742481X/>