fat binary gem for Linux

[larskanis]

With the binary linux gem it's no longer necessary to install PostgreSQL client library or header files (like package libpq-dev).

Solves #480

[larskanis]

This PR currently fails with a segfault on my local machine when connecting by a TLS encrypted connection like so:

$ valgrind ruby -rpg -e "PG.connect host:'localhost'"
==513704== Invalid write of size 8
==513704==    at 0x2285E800: pgtls_close (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x2285799F: pqsecure_close (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x2283E7B2: pqDropConnection (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x228423E0: PQconnectPoll (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x2277A7EE: ??? (in /home/lars/.rvm/gems/ruby-3.3.0/gems/pg-1.5.4-x86_64-linux-gnu/lib/3.3/pg_ext.so)
==513704==    by 0x4AC5FB7: rb_nogvl (thread.c:1530)
==513704==    by 0x2277AD2D: gvl_PQconnectPoll (in /home/lars/.rvm/gems/ruby-3.3.0/gems/pg-1.5.4-x86_64-linux-gnu/lib/3.3/pg_ext.so)
==513704==    by 0x227833F5: ??? (in /home/lars/.rvm/gems/ruby-3.3.0/gems/pg-1.5.4-x86_64-linux-gnu/lib/3.3/pg_ext.so)
==513704==    by 0x4B18FC3: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3490)
==513704==    by 0x4B1A3AA: vm_call_symbol (vm_insnhelper.c:3953)
==513704==    by 0x4AFD436: vm_sendish (vm_insnhelper.c:5581)
==513704==    by 0x4AFD436: vm_exec_core (insns.def:834)
==513704==    by 0x4AF9CDC: rb_vm_exec (vm.c:2486)
==513704==  Address 0x222d9f60 is 1,008 bytes inside a block of size 1,192 free'd
==513704==    at 0x484810F: free (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==513704==    by 0x22A86323: CRYPTO_free (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x22A121B8: sock_free (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x22A05F2F: BIO_free (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x22A0791F: BIO_free_all (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x2295A79D: ossl_ssl_connection_free (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x2295A249: SSL_free (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x2285E7FB: pgtls_close (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x2285799F: pqsecure_close (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x2283E7B2: pqDropConnection (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x228423E0: PQconnectPoll (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x2277A7EE: ??? (in /home/lars/.rvm/gems/ruby-3.3.0/gems/pg-1.5.4-x86_64-linux-gnu/lib/3.3/pg_ext.so)
==513704==  Block was alloc'd at
==513704==    at 0x4845828: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==513704==    by 0x228443E6: makeEmptyPGconn (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x2283EE00: PQconnectStart (in /home/lars/comcard/ruby-pg/ports/x86_64-linux-gnu/lib/libpq.so.5.16)
==513704==    by 0x2277A7CB: ??? (in /home/lars/.rvm/gems/ruby-3.3.0/gems/pg-1.5.4-x86_64-linux-gnu/lib/3.3/pg_ext.so)
==513704==    by 0x4AC5FB7: rb_nogvl (thread.c:1530)
==513704==    by 0x2277ACD5: gvl_PQconnectStart (in /home/lars/.rvm/gems/ruby-3.3.0/gems/pg-1.5.4-x86_64-linux-gnu/lib/3.3/pg_ext.so)
==513704==    by 0x22780B76: ??? (in /home/lars/.rvm/gems/ruby-3.3.0/gems/pg-1.5.4-x86_64-linux-gnu/lib/3.3/pg_ext.so)
==513704==    by 0x4B18FC3: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3490)
==513704==    by 0x4AFD436: vm_sendish (vm_insnhelper.c:5581)
==513704==    by 0x4AFD436: vm_exec_core (insns.def:834)
==513704==    by 0x4AF9CDC: rb_vm_exec (vm.c:2486)
==513704==    by 0x4968A52: rb_ec_exec_node (eval.c:287)
==513704==    by 0x4968A52: ruby_run_node (???:328)
==513704==    by 0x109204: rb_main (main.c:39)
==513704==    by 0x109204: main (main.c:58)
==513704== 

[larskanis]

The OpenSSL issue above is resolved by #598. CI on Fedora and Alpine Linux is running and succeeds now.

The implementation is like so:

• The cross build task builds krb5 and openssl as static libraries and link them to libpq.
• It uses a dedicated shared object name: libpq-ruby-pg.so.1. This avoids mistakenly loaded system libpq files.
• All supported ruby versions in the gem (2.7 to 3.3) link to one and the same shared object libpq-ruby-pg.so.1 to save space compared to static linking libpq into each extension file.
• A $ORIGIN-relative rpath is the mechanism to locate and load the shared object file. It seems to be solid.
• Only one binary gem with platform x86_64-linux is used, even for Musl based systems (Alpine Linux).
• Only x86_64-linux is additional supported right now by this PR.
• x86-mingw32, x64-mingw32 and x64-mingw-ucrt are now built per mini_portile2, but the result is the same as the previous Rakefile.cross.

The x86_64-linux gem runs on Alpine Linux, but requires the package gcompat there as long as we don't provide a native gem for platform x86_64-linux-musl. It is a very small package and it seems quite common, since nokogiri needs it too.

Providing a binary package adds the responsibility to update the gem in case of security updates to krb5, openssl or libpq. This was already the case for the Windows binary gems, but the new platform makes it more significant.

There is one use case the binary gem doesn't support: Retrieval of connection options from LDAP. To support this libldap would be necessary, but it has a lot of dependencies. I don't think it's a widely used feature and that it's worth to support it. If it's necessary the source gem can be forced.

So after more than one year I think this is ready to be merged.

To make sure, the new platform and the source gem is fetched by bundler, it can be added like so

bundle lock --add-platform x86_64-linux
bundle lock --add-platform ruby

to the Gemfile.lock and using a recent bundler version should do the trick.

Or if this doesn't work for some reason, forcing the usage of the source gem in the Gemfile:

gem "pg", force_ruby_platform: true

Or installing the source gem manually:

gem inst --platform ruby pg