Free Pascal on OSv

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OSv

OSv is an operating system based on Linux optimized for the cloud. Official page It runs a single application together with a small kernel and all needed libraries in a virtual machine. That means to run OSv applications you need to install a hypervisor such as QEMU/KVM or VirtualBox.

Installation

Install OSv on Linux

This worked on 3rd Mar 2015 on Ubuntu 14.10 and on 3rd Sep 2016 on Ubuntu 16.04:

Please read http://osv.io/run-locally/. Especially about the "Data collection".

Downloading capstan to ~/bin/capstan:

curl https://raw.githubusercontent.com/cloudius-systems/capstan/master/scripts/download | bash

Install needed qemu-kvm (VirtualBox is also possible, but not handled in this document)

sudo apt-get install qemu-kvm

Building an instance with capstan

Capstan takes a basic image and adds your libraries to create a VM image. It then starts the VM and runs the 'main' function of your library. At the moment only Linux/amd64 dynamic libraries with PIC are supported.

Capstanfile

Capstan needs a config file named Capstanfile. Read here for details.

Create a directory for the example. For instance ~/osv_fpc_test.

Here is an example config for a hello world program (~/osv_fpc_test/Capstanfile):

# Name of the base image. Capstan will download this automatically from Capstan repository. 
base: cloudius/osv-base

# The command line passed to OSv to start up the application.
cmdline: /tools/hello.so

# The command used to build the application.
build: ./compile.sh

# List of files that are included in the generated image.
files:
  /tools/hello.so: hello.so

Pascal Library

The small Linux kernel does not support all syscalls needed by the default FPC Linux System unit.

See here for some details what OSv does not support: https://github.com/cloudius-systems/osv/wiki/Porting-native-applications-to-OSv

You need to build the System unit using Libc (tested with fpc trunk revision 34418):

cd fpc_src_3.1.1
make clean all OPT='-dFPC_USE_LIBC -Fl/usr/lib/gcc/x86_64-linux-gnu/5'
sudo make install INSTALL_PREFIX=/usr

hello.pas

library hello;
 
// start function for OSv
function main: longint; cdecl;
begin
  Writeln('It works!');
  main:=0;
end;
 
exports main name 'main'; // OSv searches for 'main' in the library
 
end.

Here is the ~/osv_fpc_test/compile.sh:

#!/bin/bash
# create a dynamically linked library hello.so
/usr/lib/fpc/3.1.1/ppcx64 -fPIC -XD -Xc -gw2 -ohello.so hello.pas

Building

Note: The first time you build, capstan will download the base VM image "cloudius/osv-base" (~/.capstan/).

[]$ cd ~/osv_fpc_test
[]$ ~/bin/capstan build
Building osv...
Uploading files...
1 / 1 [===================================] 100.00 %

Running

[]$ ~/bin/capstan run
Created instance: helloworld
OSv v0.18
eth0: 192.168.122.15
It works!


Pascal Library without using the System unit

As demonstration here is a library, that does not call the system unit (works the normal FPC system unit):

hello.pas

Here is the ~/osv_fpc_test/hello.pas:

library hello;
 
uses
  unixtype;
 
// use the C function 'write'
function CWrite(fd : cInt; buf:pChar; nbytes : unixtype.TSize): TSsize;  external name 'write';
 
// start function for OSv
function main: longint; cdecl;
const
  MyText: PChar = 'It works!'#10;
begin
  CWrite(StdOutputHandle,MyText,strlen(MyText));
  main:=0;
end;
 
exports main name 'main'; // OSv searches for 'main' in the library
 
end.

Compile a library that does not call the system init

Here is the ~/osv_fpc_test/compile.sh:

#!/bin/bash

# compile without linking, create a dynamically linked library hello.so
fpc -fPIC -XD -Xc -g -s -ohello.so hello.pas
# link without -init FPC_SHARED_LIB_START -fini FPC_LIB_EXIT
/usr/bin/ld -b elf64-x86-64 -m elf_x86_64 -soname hello.so -shared -L. -o hello.so link.res

Building

Note: The first time you build, capstan will download the base VM image "cloudius/osv-base" (~/.capstan/).

[]$ cd ~/osv_fpc_test
[]$ ~/bin/capstan build
Building osv...
Uploading files...
1 / 1 [===================================] 100.00 %

Running

[]$ cd ~/osv_fpc_test
[]$ ~/bin/capstan run
Created instance: osv
OSv v0.18
eth0: 192.168.122.15
It works!