Cross-compile from x86_64 linux to RISC-V linux

[sestigio]

Hello, I am new using Alire and I am trying to make a university project with Ada but I have this problem.

My goal is to create a binary that can run on a MilkV Duo-S board that was a linux buildroot distro installed, in one of its two RISC-V 64 bits IMAFDC cores (C906 processor) by compiling the code on an x86_64 computer (linux ubuntu virtual machine run from Windows). The program is simple, using an ads file and a C file to take advantage from the language interfacing that Ada allows, I declare a constant in the ads file that is exported to a C file that prints it in the terminal.

The source files:

Main file written in C called prueba7.c :

#include <stdio.h>

extern int adaNumber;

int main() {
    printf("The value of MY_CONSTANT is: %d\n", adaNumber);
    return 0;
}

Ada specification file called alib.ads :

with Interfaces.C;
package alib is

Ada_Number : constant Integer := 42
	with Export, Convention => C, External_Name => "adaNumber";
		
end alib;

The attempt:

Run alr init:

alr init --bin prueba7

Add the following lines to prueba7.gpr:

for Target use "riscv64-elf";
for Runtime ("Ada") use "light-rv64imafdc";
for Languages use ("ada", "c");

Modify the following line in prueba7.gpr:

Change for Main use ("prueba7.ads"); to for Main use ("prueba7.c"); since the main program is the C file, while the Ada program is only an ads file with the exported constant.

Change the toolchain to compile in RISC-V:

alr toolchain --select and then I select the gnat_riscv64_elf=14.2.1 toolchain and the gprbuild=22.0.1 latest gprbuild

Run alr run, receive the following error (I am ignoring the style and dependencies warnings):

user1@ub-tfg:~/Alire Projects/prueba7$ alr run
ⓘ Building prueba7=0.1.0-dev/prueba7.gpr...
Compile
   [c]            prueba7.c
   [ada]          prueba7_config.ads
   [ada]          alib.ads
alib.ads:1:16: warning: unit "Interfaces.C" is not referenced [-gnatwu]
alib.ads:4:01: (style) incorrect layout [-gnatyl]
alib.ads:5:01: (style) horizontal tab not allowed [-gnatyh]
alib.ads:6:01: (style) horizontal tab not allowed [-gnatyh]
Bind
   [gprbind]      prueba7.bexch
   [Ada]          alib.ali -n
Link
   [archive]      libprueba7.a
   [index]        libprueba7.a
   [link]         prueba7.c
/home/user1/.local/share/alire/toolchains/gnat_riscv64_elf_14.2.1_4f738310/bin/../lib/gcc/riscv64-elf/14.2.0/../../../../riscv64-elf/bin/ld: warning: cannot find entry symbol _start; defaulting to 0000000000010120
/home/user1/.local/share/alire/toolchains/gnat_riscv64_elf_14.2.1_4f738310/bin/../lib/gcc/riscv64-elf/14.2.0/../../../../riscv64-elf/bin/ld: prueba7.o: in function `main':
prueba7.c:(.text+0x14): undefined reference to `printf'
collect2: error: ld returned 1 exit status
gprbuild: link of prueba7.c failed
gprbuild: failed command was: /home/user1/.local/share/alire/toolchains/gnat_riscv64_elf_14.2.1_4f738310/bin/riscv64-elf-gcc prueba7.o b__prueba7.o /home/user1/Alire Projects/prueba7/obj/development/prueba7_config.o /home/user1/Alire Projects/prueba7/obj/development/alib.o libprueba7.a -L/home/user1/Alire Projects/prueba7/obj/development/ -L/home/user1/Alire Projects/prueba7/obj/development/ -L/home/user1/.local/share/alire/toolchains/gnat_riscv64_elf_14.2.1_4f738310/riscv64-elf/lib/gnat/light-rv64imafdc/adalib/ -static-libgcc /home/user1/.local/share/alire/toolchains/gnat_riscv64_elf_14.2.1_4f738310/riscv64-elf/lib/gnat/light-rv64imafdc/adalib/libgnat.a -Wl,-L/home/user1/.local/share/alire/toolchains/gnat_riscv64_elf_14.2.1_4f738310/riscv64-elf/lib/gnat/light-rv64imafdc//adalib -nostartfiles -nolibc -L/home/user1/.local/share/alire/toolchains/gnat_riscv64_elf_14.2.1_4f738310/riscv64-elf/lib/gnat/light-rv64imafdc//ld_user -march=rv64imafdc -mabi=lp64d -fno-tree-loop-distribute-patterns -o /home/user1/Alire Projects/prueba7/bin//prueba7
error: Command ["gprbuild", "-s", "-j0", "-p", "-P", "/home/user1/Alire Projects/prueba7/prueba7.gpr"] exited with code 4
error: Build failed

I was able to run this program when I compile it using the native toolchain, so the source code should be fine. Any help is greatly appreciated!

[godunko]

Hello,

You question seems not related for Alire itself, so I suggest to discuss it in another place. Ada Forum or Reddit, for example.

Initial setup to start to use of Ada is a bit tricky, you can take a look at my experiment, see

https://github.com/godunko/sg2002-sandbox

[mosteo]

You can also try the chat rooms at https://app.element.io/#/room/#ada-lang_Lobby:gitter.im

[sestigio]

Thank you for the answers!
It's true that the whole problem does not seem Alire related, but there are two underlying questions to it that actually are and I did not ask:

When using the light runtimes from the Risc-V Alire toolchain, I always have to provide the startup and linker scripts for the particular board, do I? I did not provide them in the gpr file.
Also, does the startup-gen tool for Alire only generate scripts for bare-metal targets? Since I'm using a Linux based OS on my board, I think I need to look somewhere else.

[Fabien-Chouteau]

The gnat_riscv64_elf toolchain is for baremetal only. There are no pre-compiled GNAT cross compiler for RISC-V Linux that I know of.
You can check if there is one in the RISC-V Linux distrib your are using. Typically Ubuntu/debian provide GNAT compilers.