FPC and Apache Modules

About

How the bindings work

A basic apache module created with Free Pascal will have a code similar to this:

library mod_hello;

{$l hello_module.o}

uses
 classes,
 httpd,
 minimain in 'minimain.pas';

var
 hello_module: module; {$ifdef Unix}cvar; external; {$endif}
 default_module_ptr: Pmodule;

{$ifdef Win32}
exports
 hello_module name 'hello_module';
{$endif}

begin
  default_module_ptr := @hello_module;
  FillChar(default_module_ptr^, SizeOf(default_module_ptr^), 0);
  with default_module_ptr^ do
  begin
    version := MODULE_MAGIC_NUMBER_MAJOR;
    minor_version := MODULE_MAGIC_NUMBER_MINOR;
    module_index := -1;
    name := 'mod_hello.so';
    magic := MODULE_MAGIC_COOKIE;
  end;
end.

Apache uses a non-standard way to exchange information between the module and the library. Normally libraries export functions, but Apache instead expects a library that exports a variable. The variable is a structure with the module information. This variable needs to be filled with information as soon as the module is loaded.

Now, on Windows we can easely export a variable with Free Pascal. Just put it on the exports section. On Linux, Free Pascal doesn´t yet support exporting variables, so we need a alternative. To work around this we can create a assembler file that will export the variable and then link it into our code.

The file will look like this:

[SECTION .data]
global hello_module
hello_module dd 0

And the command line to compile this assembler code is: "nasm -f elf hello_module.asm"

Authors

Felipe Monteiro de Carvalho

Download

Status: Under development

CVS

Not yet available.

Bug Reporting

Tests are necessary to verify if all functions and structures are declared properly.

You can post Bug Reports here:

Help

Please send help requests to the Free Pascal mailling list.