Gerbil Scheme

Gerbil on MacOS

To install gerbil on MacOS the easy way is simply to download the homebrew .rb and run it as such.

wget https://raw.githubusercontent.com/mighty-gerbils/gerbil/master/homebrew/gerbil-scheme.rb
brew install --formula -vd gerbil-scheme.rb

The run the bleeding edge master build simply pass the --HEAD argument.

brew install --HEAD --formula -vd gerbil-scheme.rb

When updating/upgrading or hacking it's often needed to clear things.

  brew unlink gerbil-scheme
  # Clear the build cache. Helps with subtrees and versions
  rm -rf $(brew --cache)/gerbil-scheme--git

And, if worse comes to Worcestershire, uninstall and delete the rest.

brew uninstall gerbil-scheme
rm -rf ~/.gerbil

Documentation

Gerbil is fully available for MacOS! There are some differences that need to be taken into account should you wish to compile and distribute a binary but it should JustWork(tm) all things considered.

DYLD_LIBRARY_PATH and stripping: System Integrity Protection (SIP)

Ah stripping. Whether you love it or hate it, it happens, often witout a say. System Integrity Protection (SIP) in macOS protects the entire system by preventing the execution of unauthorized code.

In short the mantra is "Don't Shell Out!". The environment is propagated when just calling gxi.

% gxi -e '(displayln (getenv "DYLD_LIBRARY_PATH" #f))'
/opt/homebrew/Cellar/gerbil-scheme/17.9/v0.17.0-314-ga7358fcb/lib/

It may not propagate with a shebang or other reasons. It seems arbitrary. For example I updated my older iMac to an unsupported Ventura. It does not strip for me.

$ uname -a
Darwin drewc-iMac.local 22.6.0 Darwin Kernel Version 22.6.0: Tue Aug 15 20:13:24 PDT 2023; root:xnu-8796.141.3.700.5~2/RELEASE_X86_64 x86_64
$ export MY_LIBRARY_PATH=$(gxi -e '(display (path-expand "~~lib"))' -e '(flush-output-port)')
$ LD_LIBRARY_PATH=${MY_LIBRARY_PATH}
$ DYLD_LIBRARY_PATH=${MY_LIBRARY_PATH}
$ echo '#!/bin/sh' > /tmp/foo
$ echo 'echo dy?: $DYLD_LIBRARY_PATH' >> /tmp/foo
$ echo 'echo ld?: $LD_LIBRARY_PATH' >> /tmp/foo
$ echo 'echo my?: $MY_LIBRARY_PATH' >> /tmp/foo
$ chmod 755 /tmp/foo
$ /tmp/foo
dy?: /usr/local/Cellar/gerbil-scheme/HEAD-a7358fc/v0.17.0-314-ga7358fcb/lib/
ld?: /usr/local/Cellar/gerbil-scheme/HEAD-a7358fc/v0.17.0-314-ga7358fcb/lib/
my?: /usr/local/Cellar/gerbil-scheme/HEAD-a7358fc/v0.17.0-314-ga7358fcb/lib/

Whereas my Mac Mini, also running Ventura, does indeed strip.

% uname -a
Darwin users-Mac-mini.local 22.4.0 Darwin Kernel Version 22.4.0: Mon Mar  6 21:00:41 PST 2023; root:xnu-8796.101.5~3/RELEASE_ARM64_T8103 arm64
% export MY_LIBRARY_PATH=$(gxi -e '(display (path-expand "~~lib"))' -e '(flush-output-port)')
% DYLD_LIBRARY_PATH=${MY_LIBRARY_PATH}
% LD_LIBRARY_PATH=${MY_LIBRARY_PATH}
% export DYLD_LIBRARY_PATH LD_LIBRARY_PATH
% echo '#!/bin/sh' > /tmp/foo
% echo 'echo dy?: $DYLD_LIBRARY_PATH' >> /tmp/foo
% echo 'echo ld?: $LD_LIBRARY_PATH' >> /tmp/foo
% echo 'echo my?: $MY_LIBRARY_PATH' >> /tmp/foo
% chmod 755 /tmp/foo
% /tmp/foo
dy?:
ld?: /opt/homebrew/Cellar/gerbil-scheme/17.9/v0.17.0-314-ga7358fcb/lib/
my?: /opt/homebrew/Cellar/gerbil-scheme/17.9/v0.17.0-314-ga7358fcb/lib/

So be cautious with DYLD_LIBRARY_PATH and friends. Even better is to pass an -rpath to ld along with a -L<library-path> for building if needed.

The Mac ld and -rpath: No strippers allowed!

Because MacOS tries to keep things SI(m)P'le often their ld is not capable of finding our .so's, .a's, or .dylib's.

To deal with that there is the -rpath parameter for Apple's ld.

-rpath path Add path to the runpath search path list for image being created. At runtime, dyld uses the runpath when searching for dylibs whose load path begins with @rpath/.

What does that mean? In MacOS, every dynamic library has an install name. Now, Xcode seems to do it a certain way. But we are not Xcode and I do not even know what is is or what it entails.

In linux we can just set the LD_LIBRARY_PATH if needed but really it does so much magic to find libraries that it's fairly easy to get by without setting much of anything.

In MacOS there's the often stripped and must be manually propagated DYLD_LIBRARY_PATH.

I think there's a great workaround where we can define an rpath relative to the execuable path! There's some more information available here.

Unsupported Upgrades

My first real Apple Computer was a 2012 iMac. But I got it mid-2023. So I wanted to upgrade by installing MacOS on an unsupported Mac. It worked but there are a few things different about it.

Here's where I put some workarounds and hacks.

alias otool=/Library/Developer/CommandLineTools/usr/bin/otool

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