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FFI::Platypus::DL(3pm) User Contributed Perl Documentation FFI::Platypus::DL(3pm)

NAME

FFI::Platypus::DL - Slightly non-portable interface to libdl

VERSION

version 0.98

SYNOPSIS

 use FFI::Platypus;
 use FFI::Platypus::DL;
 
 my $handle = dlopen("./libfoo.so", RTLD_PLATYPUS_DEFAULT);
 my $address = dlsym($handle, "my_function_named_foo");
 my $ffi = FFI::Platypus->new;
 $ffi->function($address => [] => 'void')->call;
 dlclose($handle);

DESCRIPTION

This module provides an interface to libdl, the dynamic loader on UNIX. The underlying interface has always been used by FFI::Platypus, but it wasn't a public interface until version 0.52. The name was changed with that version when it became a public interface, so be sure to specify that version if you are going to use it.

It is somewhat non-portable for these reasons:

GNU extensions
It provides some GNU extensions to platforms such as Linux that support them.
Windows
It provides an emulation layer on Windows. The emulation layer only supports "RTLD_PLATYPUS_DEFAULT" as a flag. The emulation layer emulates the convention described below of passing "undef" as the dynamic library name to mean, use the currently running executable. I've used it without any problems for years, but Windows is not my main development platform.

FUNCTIONS

dlopen

 my $handle = dlopen($filename, $flags);

This opens a dynamic library in the context of the dynamic loader. $filename is the full or relative path to a dynamic library (usually a ".so" on Linux and some other UNIXen, a ".dll" on Windows and a ".dylib" on OS X). $flags are flags that can be used to alter the behavior of the library and the symbols it contains. The return value is an opaque pointer or $handle which can be used to look up symbols with "dlsym". The handle should be closed with "dlclose" when you are done with it.

By convention if you pass in "undef" for the filename, the currently loaded executable will be used instead of a separate dynamic library. This is the easiest and most portable way to find the address of symbols in the standard C library. This convention is baked into most UNIXen, but this capability is emulated in Windows which doesn't come with the capability out of the box.

If there is an error in opening the library then "undef" will be returned and the diagnostic for the failure can be retrieved with "dlerror" as described below.

Not all flags are supported on all platforms. You can test if a flag is available using can:

 if(FFI::Platypus::DL->can('RTLD_LAZY'))
 {
   ...
 }

Typically where flags are not mutually exclusive, they can be or'd together:

 my $handle = dlopen("libfoo.so", RTLD_LAZY | RTLD_GLOBAL);

Check your operating system documentation for detailed descriptions of these flags.

RTLD_PLATYPUS_DEFAULT
This is the FFI::Platypus default for "dlopen" (NOTE: NOT the libdl default). This is the only flag supported on Windows. For historical reasons, this is usually "RTLD_LAZY" on Unix and 0 on Windows.
RTLD_LAZY
Perform lazy binding.
RTLD_NOW
Resolve all symbols before returning from "dlopen". Error if all symbols cannot resolve.
RTLD_GLOBAL
Symbols are shared.
RTLD_LOCAL
Symbols are NOT shared.
RTLD_NODELETE
glibc 2.2 extension.
RTLD_NOLOAD
glibc 2.2 extension.
RTLD_DEEPBIND
glibc 2.3.4 extension.

dlsym

 my $opaque = dlsym($handle, $symbol);

This looks up the given $symbol in the library pointed to by $handle. If the symbol is found, the address for that symbol is returned as an opaque pointer. This pointer can be passed into the FFI::Platypus "function" and "attach" methods instead of a function name.

If the symbol cannot be found then "undef" will be returned and the diagnostic for the failure can be retrieved with "dlerror" as described below.

dlclose

 my $status = dlclose($handle);

On success, "dlclose" returns 0; on error, it returns a nonzero value, and the diagnostic for the failure can be retrieved with "dlerror" as described below.

dlerror

 my $error_string = dlerror;

Returns the human readable diagnostic for the reason for the failure for the most recent "dl" prefixed function call.

CAVEATS

Some flags for "dlopen" are not portable. This module may not be supported platforms added to FFI::Platypus in the future. It does work as far as I know on all of the currently supported platforms.

SEE ALSO

FFI::Platypus

AUTHOR

Author: Graham Ollis <plicease@cpan.org>

Contributors:

Bakkiaraj Murugesan (bakkiaraj)

Dylan Cali (calid)

pipcet

Zaki Mughal (zmughal)

Fitz Elliott (felliott)

Vickenty Fesunov (vyf)

Gregor Herrmann (gregoa)

Shlomi Fish (shlomif)

Damyan Ivanov

Ilya Pavlov (Ilya33)

Petr Pisar (ppisar)

Mohammad S Anwar (MANWAR)

Håkon Hægland (hakonhagland, HAKONH)

Meredith (merrilymeredith, MHOWARD)

COPYRIGHT AND LICENSE

This software is copyright (c) 2015,2016,2017,2018,2019 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.

2019-10-15 perl v5.30.0