[PROF-9926] Fix rpath for linking to libdatadog when loading from extension dir (cherry-pick from 1.x-stable)

ext/datadog_profiling_native_extension/extconf.rb

@@ -211,12 +211,14 @@ def add_compiler_flag(flag)
   skip_building_extension!(Datadog::Profiling::NativeExtensionHelpers::Supported::COMPILER_ATOMIC_MISSING)
 end
 
-# See comments on the helper method being used for why we need to additionally set this.
+# See comments on the helper methods being used for why we need to additionally set this.
 # The extremely excessive escaping around ORIGIN below seems to be correct and was determined after a lot of
 # experimentation. We need to get these special characters across a lot of tools untouched...
-$LDFLAGS += \
-  ' -Wl,-rpath,$$$\\\\{ORIGIN\\}/' \
-  "#{Datadog::Profiling::NativeExtensionHelpers.libdatadog_folder_relative_to_native_lib_folder}"
+extra_relative_rpaths = [
+  Datadog::Profiling::NativeExtensionHelpers.libdatadog_folder_relative_to_native_lib_folder,
+  *Datadog::Profiling::NativeExtensionHelpers.libdatadog_folder_relative_to_ruby_extensions_folders,
+]
+extra_relative_rpaths.each { |folder| $LDFLAGS += " -Wl,-rpath,$$$\\\\{ORIGIN\\}/#{folder.to_str}" }
 Logging.message("[datadog] After pkg-config $LDFLAGS were set to: #{$LDFLAGS.inspect}\n")
 
 # Tag the native extension library with the Ruby version and Ruby platform.

ext/datadog_profiling_native_extension/native_extension_helpers.rb

@@ -67,6 +67,52 @@ def self.libdatadog_folder_relative_to_native_lib_folder(
         Pathname.new(libdatadog_lib_folder).relative_path_from(Pathname.new(profiling_native_lib_folder)).to_s
       end
 
+      # In https://github.com/DataDog/dd-trace-rb/pull/3582 we got a report of a customer for which the native extension
+      # only got installed into the extensions folder.
+      #
+      # But then this fix was not enough to fully get them moving because then they started to see the issue from
+      # https://github.com/DataDog/dd-trace-rb/issues/2067 / https://github.com/DataDog/dd-trace-rb/pull/2125 :
+      #
+      # > Profiling was requested but is not supported, profiling disabled: There was an error loading the profiling
+      # > native extension due to 'RuntimeError Failure to load datadog_profiling_native_extension.3.2.2_x86_64-linux
+      # > due to libdatadog_profiling.so: cannot open shared object file: No such file or directory
+      #
+      # The problem is that when loading the native extension from the extensions directory, the relative rpath we add
+      # with the #libdatadog_folder_relative_to_native_lib_folder helper above is not correct, we need to add a relative
+      # rpath to the extensions directory.
+      #
+      # So how do we find the full path where the native extension is placed?
+      # * From https://github.com/ruby/ruby/blob/83f02d42e0a3c39661dc99c049ab9a70ff227d5b/lib/bundler/runtime.rb#L166
+      #   `extension_dirs = Dir["#{Gem.dir}/extensions/*/*/*"] + Dir["#{Gem.dir}/bundler/gems/extensions/*/*/*"]`
+      #   we get that's in one of two fixed subdirectories of `Gem.dir`
+      # * From https://github.com/ruby/ruby/blob/83f02d42e0a3c39661dc99c049ab9a70ff227d5b/lib/rubygems/basic_specification.rb#L111-L115
+      #   we get the structure of the subdirectory (platform/extension_api_version/gem_and_version)
+      #
+      # Thus, `Gem.dir` of `/var/app/current/vendor/bundle/ruby/3.2.0` becomes (for instance)
+      # `/var/app/current/vendor/bundle/ruby/3.2.0/extensions/x86_64-linux/3.2.0/datadog-2.0.0/` or
+      # `/var/app/current/vendor/bundle/ruby/3.2.0/bundler/gems/extensions/x86_64-linux/3.2.0/datadog-2.0.0/`
+      #
+      # We then compute the relative path between these folders and the libdatadog folder, and use that as a relative path.
+      def self.libdatadog_folder_relative_to_ruby_extensions_folders(
+        gem_dir: Gem.dir,
+        libdatadog_pkgconfig_folder: Libdatadog.pkgconfig_folder
+      )
+        return unless libdatadog_pkgconfig_folder
+
+        # For the purposes of calculating a folder relative to the other, we don't actually NEED to fill in the
+        # platform, extension_api_version and gem version. We're basically just after how many folders it is deep from
+        # the Gem.dir.
+        expected_ruby_extensions_folders = [
+          "#{gem_dir}/extensions/platform/extension_api_version/datadog_version/",
+          "#{gem_dir}/bundler/gems/extensions/platform/extension_api_version/datadog_version/",
+        ]
+        libdatadog_lib_folder = "#{libdatadog_pkgconfig_folder}/../"
+
+        expected_ruby_extensions_folders.map do |folder|
+          Pathname.new(libdatadog_lib_folder).relative_path_from(Pathname.new(folder)).to_s
+        end
+      end
+
       # Used to check if profiler is supported, including user-visible clear messages explaining why their
       # system may not be supported.
       module Supported

spec/datadog/profiling/native_extension_helpers_spec.rb

@@ -33,6 +33,47 @@
     end
   end
 
+  describe '.libdatadog_folder_relative_to_ruby_extensions_folders' do
+    context 'when libdatadog is available' do
+      before do
+        skip_if_profiling_not_supported(self)
+        if PlatformHelpers.mac? && Libdatadog.pkgconfig_folder.nil? && ENV['LIBDATADOG_VENDOR_OVERRIDE'].nil?
+          raise 'You have a libdatadog setup without macOS support. Did you forget to set LIBDATADOG_VENDOR_OVERRIDE?'
+        end
+      end
+
+      it 'returns a relative path to libdatadog folder from the ruby extensions folders' do
+        extensions_relative, bundler_extensions_relative =
+          described_class.libdatadog_folder_relative_to_ruby_extensions_folders
+
+        libdatadog_extension = RbConfig::CONFIG['SOEXT'] || raise('Missing SOEXT for current platform')
+        libdatadog = "libdatadog_profiling.#{libdatadog_extension}"
+
+        expect(extensions_relative).to start_with('../')
+        expect(bundler_extensions_relative).to start_with('../')
+
+        extensions_full =
+          "#{Gem.dir}/extensions/platform/extension_api_version/datadog_version/#{extensions_relative}/#{libdatadog}"
+        bundler_extensions_full =
+          "#{Gem.dir}/bundler/gems/extensions/platform/extension_api_version/datadog_version/" \
+          "#{bundler_extensions_relative}/#{libdatadog}"
+
+        expect(File.exist?(Pathname.new(extensions_full).cleanpath.to_s))
+          .to be(true), "Libdatadog not available in expected path: #{extensions_full.inspect}"
+        expect(File.exist?(Pathname.new(bundler_extensions_full).cleanpath.to_s))
+          .to be(true), "Libdatadog not available in expected path: #{bundler_extensions_full.inspect}"
+      end
+    end
+
+    context 'when libdatadog is unsupported' do
+      it do
+        expect(
+          described_class.libdatadog_folder_relative_to_ruby_extensions_folders(libdatadog_pkgconfig_folder: nil)
+        ).to be nil
+      end
+    end
+  end
+
   describe '::LIBDATADOG_VERSION' do
     it 'must match the version restriction set on the gemspec' do
       # This test is expected to break when the libdatadog version on the .gemspec is updated but we forget to update