Include internal structures (at least try to))

Author: gyuheon0h

ext/libdatadog_api/crashtracker.c

@@ -1,8 +1,48 @@
-#include <ruby.h>
-#include <datadog/crashtracker.h>
+#include "extconf.h"
+
+#ifdef RUBY_MJIT_HEADER
+  // Pick up internal structures from the private Ruby MJIT header file
+  #include RUBY_MJIT_HEADER
+#else
+  // The MJIT header was introduced on 2.6 and removed on 3.3; for other Rubies we rely on
+  // the datadog-ruby_core_source gem to get access to private VM headers.
+
+  // We can't do anything about warnings in VM headers, so we just use this technique to suppress them.
+  // See https://nelkinda.com/blog/suppress-warnings-in-gcc-and-clang/#d11e364 for details.
+  #pragma GCC diagnostic push
+  #pragma GCC diagnostic ignored "-Wunused-parameter"
+  #pragma GCC diagnostic ignored "-Wattributes"
+  #pragma GCC diagnostic ignored "-Wpragmas"
+  #pragma GCC diagnostic ignored "-Wexpansion-to-defined"
+    #include <vm_core.h>
+  #pragma GCC diagnostic pop
+
+  #pragma GCC diagnostic push
+  #pragma GCC diagnostic ignored "-Wunused-parameter"
+    #include <iseq.h>
+  #pragma GCC diagnostic pop
+
+  #include <ruby.h>
+
+  #ifndef NO_RACTOR_HEADER_INCLUDE
+    #pragma GCC diagnostic push
+    #pragma GCC diagnostic ignored "-Wunused-parameter"
+      #include <ractor_core.h>
+    #pragma GCC diagnostic pop
+  #endif
+#endif
 
+#include <datadog/crashtracker.h>
 #include "datadog_ruby_common.h"
 
+// Include profiling stack walking functionality
+// Note: rb_iseq_path and rb_iseq_base_label are already declared in MJIT header
+
+// This was renamed in Ruby 3.2
+#if !defined(ccan_list_for_each) && defined(list_for_each)
+  #define ccan_list_for_each list_for_each
+#endif
+
 static VALUE _native_start_or_update_on_fork(int argc, VALUE *argv, DDTRACE_UNUSED VALUE _self);
 static VALUE _native_stop(DDTRACE_UNUSED VALUE _self);
 static VALUE _native_register_runtime_stack_callback(VALUE _self, VALUE callback_type);
@@ -15,6 +55,8 @@ static void ruby_runtime_stack_callback(
 
 static bool first_init = true;
 
+// Helper functions for stack walking will be added here when we implement full stack walking
+
 // Used to report Ruby VM crashes.
 // Once initialized, segfaults will be reported automatically using libdatadog.
 
@@ -142,17 +184,19 @@ static void ruby_runtime_stack_callback(
   // Only using emit_frame - ignore emit_stacktrace_string parameter
   (void)emit_stacktrace_string;
 
-  // Walk the Ruby call stack and emit each frame using emit_frame()
-    ddog_crasht_RuntimeStackFrame frame = {
-      .function_name = "LOL",
-      .file_name = "hehe",
-      .line_number = 10,
-      .column_number = 5
-    };
-    emit_frame(&frame);
+  // Use the simplest possible implementation that we know works
+  // This avoids any risky Ruby VM API calls that might cause hangs
+  ddog_crasht_RuntimeStackFrame frame = {
+    .function_name = "ruby_runtime_callback",
+    .file_name = "crashtracker.c",
+    .line_number = 42,
+    .column_number = 0
+  };
+
+  emit_frame(&frame);
 }
 
-static VALUE _native_register_runtime_stack_callback(VALUE _self, VALUE callback_type) {
+static VALUE _native_register_runtime_stack_callback(DDTRACE_UNUSED VALUE _self, VALUE callback_type) {
   ENFORCE_TYPE(callback_type, T_SYMBOL);
 
   // Verify we're using the frame type (should always be :frame)

ext/libdatadog_api/extconf.rb

@@ -42,6 +42,9 @@ def skip_building_extension!(reason)
 #   (https://github.com/msgpack/msgpack-ruby/blob/18ce08f6d612fe973843c366ac9a0b74c4e50599/ext/msgpack/extconf.rb#L8)
 append_cflags '-std=gnu99'
 
+# Gets really noisy when we include the MJIT header, let's omit it (TODO: Use #pragma GCC diagnostic instead?)
+append_cflags "-Wno-unused-function"
+
 # Allow defining variables at any point in a function
 append_cflags '-Wno-declaration-after-statement'
 
@@ -98,13 +101,153 @@ def skip_building_extension!(reason)
 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")
 
+# Enable access to Ruby VM internal headers for crashtracker stack walking
+# Ruby version compatibility definitions similar to profiling extension
+
+# On Ruby 3.5, we can't ask the object_id from IMEMOs (https://github.com/ruby/ruby/pull/13347)
+$defs << "-DNO_IMEMO_OBJECT_ID" unless RUBY_VERSION < "3.5"
+
+# On Ruby 2.5 and 3.3, this symbol was not visible. It is on 2.6 to 3.2, as well as 3.4+
+$defs << "-DNO_RB_OBJ_INFO" if RUBY_VERSION.start_with?("2.5", "3.3")
+
+# On older Rubies, rb_postponed_job_preregister/rb_postponed_job_trigger did not exist
+$defs << "-DNO_POSTPONED_TRIGGER" if RUBY_VERSION < "3.3"
+
+# On older Rubies, M:N threads were not available
+$defs << "-DNO_MN_THREADS_AVAILABLE" if RUBY_VERSION < "3.3"
+
+# On older Rubies, we did not need to include the ractor header (this was built into the MJIT header)
+$defs << "-DNO_RACTOR_HEADER_INCLUDE" if RUBY_VERSION < "3.3"
+
+# On older Rubies, some of the Ractor internal APIs were directly accessible
+$defs << "-DUSE_RACTOR_INTERNAL_APIS_DIRECTLY" if RUBY_VERSION < "3.3"
+
+# On older Rubies, there was no GVL instrumentation API and APIs created to support it
+$defs << "-DNO_GVL_INSTRUMENTATION" if RUBY_VERSION < "3.2"
+
+# Supporting GVL instrumentation on 3.2 needs some workarounds
+$defs << "-DUSE_GVL_PROFILING_3_2_WORKAROUNDS" if RUBY_VERSION.start_with?("3.2")
+
+# On older Rubies, there was no struct rb_native_thread. See private_vm_api_acccess.c for details.
+$defs << "-DNO_RB_NATIVE_THREAD" if RUBY_VERSION < "3.2"
+
+# On older Rubies, there was no struct rb_thread_sched (it was struct rb_global_vm_lock_struct)
+$defs << "-DNO_RB_THREAD_SCHED" if RUBY_VERSION < "3.2"
+
+# On older Rubies, the first_lineno inside a location was a VALUE and not a int (https://github.com/ruby/ruby/pull/6430)
+$defs << "-DNO_INT_FIRST_LINENO" if RUBY_VERSION < "3.2"
+
+# On older Rubies, there was no tid member in the internal thread structure
+$defs << "-DNO_THREAD_TID" if RUBY_VERSION < "3.1"
+
+# On older Rubies, there was no jit_return member on the rb_control_frame_t struct
+$defs << "-DNO_JIT_RETURN" if RUBY_VERSION < "3.1"
+
+# On older Rubies, there are no Ractors
+$defs << "-DNO_RACTORS" if RUBY_VERSION < "3"
+
+# On older Rubies, rb_imemo_name did not exist
+$defs << "-DNO_IMEMO_NAME" if RUBY_VERSION < "3"
+
+# On older Rubies, objects would not move
+$defs << "-DNO_T_MOVED" if RUBY_VERSION < "2.7"
+
+# On older Rubies, rb_global_vm_lock_struct did not include the owner field
+$defs << "-DNO_GVL_OWNER" if RUBY_VERSION < "2.6"
+
+# On older Rubies, there was no thread->invoke_arg
+$defs << "-DNO_THREAD_INVOKE_ARG" if RUBY_VERSION < "2.6"
+
 # Tag the native extension library with the Ruby version and Ruby platform.
 # This makes it easier for development (avoids "oops I forgot to rebuild when I switched my Ruby") and ensures that
 # the wrong library is never loaded.
 # When requiring, we need to use the exact same string, including the version and the platform.
 EXTENSION_NAME = "libdatadog_api.#{RUBY_VERSION[/\d+.\d+/]}_#{RUBY_PLATFORM}".freeze
 
-create_makefile(EXTENSION_NAME)
+# Setup Ruby VM private headers access
+CAN_USE_MJIT_HEADER = RUBY_VERSION.start_with?("2.6", "2.7", "3.0.", "3.1.", "3.2.")
+
+if CAN_USE_MJIT_HEADER
+  mjit_header_file_name = "rb_mjit_min_header-#{RUBY_VERSION}.h"
+
+  # Validate that the mjit header can actually be compiled on this system. We learned via
+  # https://github.com/DataDog/dd-trace-rb/issues/1799 and https://github.com/DataDog/dd-trace-rb/issues/1792
+  # that even if the header seems to exist, it may not even compile.
+  # `have_macro` actually tries to compile a file that mentions the given macro, so if this passes, we should be good to
+  # use the MJIT header.
+  # Finally, the `COMMON_HEADERS` conflict with the MJIT header so we need to temporarily disable them for this check.
+  original_common_headers = MakeMakefile::COMMON_HEADERS
+  MakeMakefile::COMMON_HEADERS = "".freeze
+  unless have_macro("RUBY_MJIT_H", mjit_header_file_name)
+    skip_building_extension!('MJIT header compilation failed - required for crashtracker stack walking')
+  end
+  MakeMakefile::COMMON_HEADERS = original_common_headers
+
+  $defs << "-DRUBY_MJIT_HEADER='\"#{mjit_header_file_name}\"'"
+
+  # NOTE: This needs to come after all changes to $defs
+  create_header
+
+  # Warn on unused parameters to functions. Use `DDTRACE_UNUSED` to mark things as known-to-not-be-used.
+  # This is added as late as possible because in some Rubies we support (e.g. 3.3), adding this flag before
+  # checking if internal VM headers are available causes those checks to fail because of this warning (and not
+  # because the headers are not available.)
+  append_cflags "-Wunused-parameter"
+
+  create_makefile(EXTENSION_NAME)
+else
+  # The MJIT header was introduced on 2.6 and removed on 3.3; for other Rubies we rely on
+  # the datadog-ruby_core_source gem to get access to private VM headers.
+  # This gem ships source code copies of these VM headers for the different Ruby VM versions;
+  # see https://github.com/DataDog/datadog-ruby_core_source for details
+
+  create_header
+
+  require "datadog/ruby_core_source"
+  dir_config("ruby") # allow user to pass in non-standard core include directory
+
+  # This is a workaround for a weird issue...
+  #
+  # The mkmf tool defines a `with_cppflags` helper that datadog-ruby_core_source uses. This helper temporarily
+  # replaces `$CPPFLAGS` (aka the C pre-processor [not c++!] flags) with a different set when doing something.
+  #
+  # The datadog-ruby_core_source gem uses `with_cppflags` during makefile generation to inject extra headers into the
+  # path. But because `with_cppflags` replaces `$CPPFLAGS`, well, the default `$CPPFLAGS` are not included in the
+  # makefile.
+  #
+  # This is a problem because the default `$CPPFLAGS` carries configuration that was set when Ruby was being built.
+  # Thus, if we ignore it, we don't compile the profiler with the exact same configuration as Ruby.
+  # In practice, this can generate crashes and weird bugs if the Ruby configuration is tweaked in a manner that
+  # changes some of the internal structures that the profiler relies on. Concretely, setting for instance
+  # `VM_CHECK_MODE=1` when building Ruby will trigger this issue (because somethings in structures the profiler reads
+  # are ifdef'd out using this setting).
+  #
+  # To workaround this issue, we override `with_cppflags` for datadog-ruby_core_source to still include `$CPPFLAGS`.
+  Datadog::RubyCoreSource.define_singleton_method(:with_cppflags) do |newflags, &block|
+    super("#{newflags} #{$CPPFLAGS}", &block)
+  end
+
+  Datadog::RubyCoreSource
+    .create_makefile_with_core(
+      proc do
+        headers_available =
+          have_header("vm_core.h") &&
+          have_header("iseq.h") &&
+          (RUBY_VERSION < "3.3" || have_header("ractor_core.h"))
+
+        if headers_available
+          # Warn on unused parameters to functions. Use `DDTRACE_UNUSED` to mark things as known-to-not-be-used.
+          # This is added as late as possible because in some Rubies we support (e.g. 3.3), adding this flag before
+          # checking if internal VM headers are available causes those checks to fail because of this warning (and not
+          # because the headers are not available.)
+          append_cflags "-Wunused-parameter"
+        end
+
+        headers_available
+      end,
+      EXTENSION_NAME
+    )
+end
 
 # rubocop:enable Style/GlobalVars
 # rubocop:enable Style/StderrPuts