Module: Datadog::Profiling::NativeExtensionHelpers

Defined in:
ext/ddtrace_profiling_native_extension/native_extension_helpers.rb

Overview

Helpers for extconf.rb

Defined Under Namespace

Modules: Supported

Constant Summary collapse

ENV_NO_EXTENSION =

Can be set when customers want to skip compiling the native extension entirely

'DD_PROFILING_NO_EXTENSION'
ENV_FAIL_INSTALL_IF_MISSING_EXTENSION =

Can be set to force rubygems to fail gem installation when profiling extension could not be built

'DD_PROFILING_FAIL_INSTALL_IF_MISSING_EXTENSION'
CAN_USE_MJIT_HEADER =

Older Rubies don’t have the MJIT header, used by the JIT compiler, so we need to use a different approach

RUBY_VERSION >= '2.6'
LIBDATADOG_VERSION = 
'~> 2.0.0.1.0'

Class Method Summary collapse

Class Method Details

.fail_install_if_missing_extension? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'ext/ddtrace_profiling_native_extension/native_extension_helpers.rb', line 20

def self.fail_install_if_missing_extension?
  ENV[ENV_FAIL_INSTALL_IF_MISSING_EXTENSION].to_s.strip.downcase == 'true'
end

.libdatadog_folder_relative_to_native_lib_folder(current_folder: __dir__, libdatadog_pkgconfig_folder: Libdatadog.pkgconfig_folder) ⇒ Object

Used as an workaround for a limitation with how dynamic linking works in environments where ddtrace and libdatadog are moved after the extension gets compiled.

Because the libddpprof native library is installed on a non-standard system path, in order for it to be found by the system dynamic linker (e.g. what takes care of dlopen(), which is used to load the profiling native extension), we need to add a “runpath” – a list of folders to search for libdatadog.

This runpath gets hardcoded at native library linking time. You can look at it using the ‘readelf` tool in Linux: e.g. `readelf -d ddtrace_profiling_native_extension.2.7.3_x86_64-linux.so`.

In older versions of ddtrace, we only set as runpath an absolute path to libdatadog. (This gets set automatically by the call to ‘pkg_config(’datadog_profiling_with_rpath’)‘ in `extconf.rb`). This worked fine as long as libdatadog was NOT moved from the folder it was present at ddtrace installation/linking time.

Unfortunately, environments such as Heroku and AWS Elastic Beanstalk move gems around in the filesystem after installation. Thus, the profiling native extension could not be loaded in these environments (see github.com/DataDog/dd-trace-rb/issues/2067) because libdatadog could not be found.

To workaround this issue, this method computes the relative path between the folder where the profiling native extension is going to be installed and the folder where libdatadog is installed, and returns it to be set as an additional runpath. (Yes, you can set multiple runpath folders to be searched).

This way, if both gems are moved together (and it turns out that they are in these environments), the relative path can still be traversed to find libdatadog.

This is incredibly awful, and it’s kinda bizarre how it’s not possible to just find these paths at runtime and set them correctly; rather than needing to set stuff at linking-time and then praying to $deity that weird moves don’t happen.

As a curiosity, ‘LD_LIBRARY_PATH` can be used to influence the folders that get searched but **CANNOT BE SET DYNAMICALLY**, e.g. it needs to be set at the start of the process (Ruby VM) and thus it’s not something we could setup when doing a ‘require`.



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# File 'ext/ddtrace_profiling_native_extension/native_extension_helpers.rb', line 58

def self.libdatadog_folder_relative_to_native_lib_folder(
  current_folder: __dir__,
  libdatadog_pkgconfig_folder: Libdatadog.pkgconfig_folder
)
  return unless libdatadog_pkgconfig_folder

  profiling_native_lib_folder = "#{current_folder}/../../lib/"
  libdatadog_lib_folder = "#{libdatadog_pkgconfig_folder}/../"

  Pathname.new(libdatadog_lib_folder).relative_path_from(Pathname.new(profiling_native_lib_folder)).to_s
end