FFI

Perl Foreign Function Interface based on libffi

SYNOPSIS

# for a more portable interface see FFI::Library
$clib_file = ($^O eq "MSWin32") ? "MSVCRT40.DLL" : "-lc";
$clib = DynaLoader::dl_findfile($clib_file);
$strlen = DynaLoader::dl_find_symbol($clib, "strlen");
$n = FFI::call($strlen, "cIp", $my_string);
DynaLoader::dl_free_file($clib);

DESCRIPTION

NOTE: Newer and better maintained FFI modules such as FFI::Platypus provide more functionality and so it is strongly recommend that you use one of them for new projects and even consider migrating to one of them for existing projects.

This module provides a low-level foreign function interface to Perl. It allows the calling of any function for which the user can supply an address and calling signature. Furthermore, it provides a method of encapsulating Perl subroutines as callback functions whose addresses can be passed to C code.

FUNCTIONS

call

my $ret = FFI::call($address, $signature, @arguments);

Call the function at the given $address with the given $signature> (see below) and the given @arguments.

callback

my $address = FFI::callback($signature, \&subref);

Creates a c callback that will call a Perl subref.

FUNCTION SIGNATURES

Function interfaces are defined by signatures. A function's signature is a string which specifies the function's return type, argument types and calling convention. The first character of the string is the function's calling convention. This is one of

s   The standard calling convention for dynamically linked functions
c   The calling convention used by C functions

Note that on many platforms, these two calling conventions may be identical. On the Windows platform, the s code corresponds to the stdcall calling convention, which is used for most dynamic link libraries. The c code corresponds to the cdecl calling convention, which is used for C functions, such as those in the C runtime library.

The remaining characters of the string are the return type of the function, followed by the argument types, in left-to-right order. Valid values are based on the codes used for the pack function, namely

c   A signed char value.
C   An unsigned char value.
s   A signed short value.
S   An unsigned short value.
i   A signed integer value.
I   An unsigned integer value.
l   A signed long value.
L   An unsigned long value.
f   A single-precision float.
d   A double-precision float.
p   A pointer to a Perl scalar.
o   A opaque pointer, ie, an address.
v   No value (only valid as a return type).

Note that all of the above codes refer to "native" format values.

The p code as an argument type simply passes the address of the Perl value's memory to the foreign function. It is the caller's responsibility to be sure that the called function does not overwrite memory outside that allocated by Perl.

The p code as a return type treats the returned value as a null-terminated string, and passes it back to Perl as such. There is currently no support for functions which return pointers to structures, or to other blocks of memory which do not contain strings, nor for functions which return memory which the caller must free.

To pass pointers to strings, use the p code. Perl ensures that strings are null-terminated for you. To pass pointers to structures, use pack. To pass an arbitrary block of memory, use something like the following:

$buf = ' ' x 100;
# Use $buf via a 'p' parameter as a 100-byte memory block

At the present time, there is no direct support for passing pointers to 'native' types (like int). To work around this, use $buf = pack('i', 12); to put an integer into a block of memory, then use the p pointer type, and obtain any returned value using $n = unpack('i', $buf); In the future, better support may be added (but remember that this is intended as a low-level interface!)

SUPPORT

Please open any support tickets with this project's GitHub repository here:

https://github.com/PerlFFI/FFI/issues

SEE ALSO

• FFI::Library

  Higher level interface to libraries using this module.

• FFI::CheckLib

  Portable functions for finding libraries.

• FFI::Platypus

  Platypus is another FFI interface based on libffi. It has a more extensive feature set, and libffi has a less restrictive license.

AUTHOR

Original author: Paul Moore gustav@morpheus.demon.co.uk

Current maintainer: Graham Ollis plicease@cpan.org

Contributors:

Anatoly Vorobey avorobey@pobox.com

Gaal Yahas gaal@forum2.org

Mitchell Charity mcharity@vendian.org

Reini Urban <RURBAN@cpan.org

COPYRIGHT AND LICENSE

This software is copyright (c) 2016-2018 by Graham Ollis.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.