I needed to distribute some RPMs with a PAR::Packer created (using pp) executable.

If you don’t know what PAR::Packer is, it is the incredibly awesome Perl 5 utility that allows you to create an executable that contains your Perl interpreter, your code, and any libraries you need.  It’s basically one of the ways you have to escape dependency hell with Perl – you can use all the wonderful CPAN modules without fear. You can use the new features of recent versions of Perl (such as subroutine signatures and enhanced performance), without worrying about what version of Perl is installed on someone else’s machine. You don’t need to worry about missing core modules in Fedora and other platforms (Fedora is missing autodie – an essential module for lazy programmers).  So building an archived executable is a great way to distribute Perl apps to people not comfortable with the Perl toolchain.

You can think of it like a Perl compiler (it’s not, but the distinction isn’t terribly important for this context).

It’s a somewhat finicky beast, and can take some effort to get it to package things the way you need them, but it’s a standard trick of the trade when I can’t just use perlbrew to build what I want on a machine. It certainly is a lot quicker to install a single executable than to compile and test hundreds of CPAN modules!

So, it seems natural to combine this with RPM. This way, users can install my stuff just by doing a simple rpm --install <file>.rpm – that’s awesome.  Well, it would be, but building an RPM with a PAR::Packer built executable doesn’t actually work, at least not on Red Hat Enterprise Linux 5 (RHEL5) or RHEL6.

Let me explain….

Take this script, hello.pl:

#!/usr/bin/env perl

use v5.22; # Use perl 5.22's features
use strict;
use warnings;

use autodie; # This causes issues on Fedora out of the box

MAIN: {
    say reverse (split //, "!dlroW olleH");
}

If I run it on most distributions, line 3 will give me an error (the OS Perl isn’t new enough). On Red Hat/Fedora installs, if I changed line 3 to support older perl interpreters, the inclusion of autodie in line 7 will error out, unless that module has already been installed.

For instance:

perldemo:demo$ ./hello.pl
Perl v5.22.0 required--this is only v5.18.2, stopped at hello.pl line 3.
BEGIN failed--compilation aborted at hello.pl line 3.

Of course it works fine when I use my local perl interpreter (a perlbrew-built 5.22.1):

perldemo:demo$ perl hello.pl
Hello World!

So, I can create a packed executable, which runs great (at least on other systems with the same system libraries – the same limitations a an executable you dynamically link and build using C):

perldemo:demo$ pp -o hello hello.pl
perldemo:demo$ ./hello
Hello World!

Perfect! Note that I ran the executable hello, not hello.pl. The hello file is a self-contained executable that doesn’t depend on the system perl.

So what happens when I put this in an RPM package?  I won’t go through the steps of building an RPM, but will let you see what error you will get when you try running the executable:

perldemo:demo$ ./hello
Usage: ./hello [ -Alib.par ] [ -Idir ] [ -Mmodule ] [ src.par ] [ program.pl ]
./hello [ -B|-b ] [-Ooutfile] src.par

What the heck? It’s expecting a PAR file to be passed to it – the PAR, or Perl ARchive, of course contains the perl interpreter, your code, and your modules – for some reason the file can’t find it.

You can duplicate this without RPM by using strip on the output of pp on Linux:

perldemo:demo$ pp -o hello hello.pl
perldemo:demo$ ./hello
Hello World!
perldemo:demo$ strip ./hello
perldemo:demo$ ./hello
Usage: ./hello [ -Alib.par ] [ -Idir ] [ -Mmodule ] [ src.par ] [ program.pl ]
./hello [ -B|-b ] [-Ooutfile] src.par

What is going on? The strip removes debugging information and the like, but generally isn’t expected to change how your program runs – but in this case it seems to be removing a lot more. Running this same strip on OSX (Apple) is enlightening:

perldemo:demo$ strip hello
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/strip: the __LINKEDIT segment does not cover the end of the file (can't be processed) in: /Users/jmaslak/pp/hello
perldemo:demo$ ./hello
Hello World!

So it appears Macs won’t strip the archive out of the extraction executable produced by pp – but Linux has no problem happily stripping it.

It turns out that standard configurations of rpmbuild on at least RHEL5 and RHEL6 automatically strip all binaries in the binary package (that’s the “standard” package you would install).

So how do you disable this evil? It turns out it’s not easy. On RHEL6, you add this near the top of your SPEC file (the SPEC file rpmbuild uses to create the RPM):

%global __os_install_post %{nil}

Now, rpmbuild won’t strip the file. But this doesn’t help RHEL5. So I added another line, that did what I want (assuming I don’t need a debug package, which I don’t in this case):

%define debug_package %{nil}
%global __os_install_post %{nil}

Sure enough, now my code does exactly what I want, even when I install the PAR executable via RPM:

perldemo:demo$ ./hello
Hello World!

Whew!