feat: OTel context sharing

Makefile

@@ -48,7 +48,7 @@ RUN_TESTS_CMD := DD_SERVICE= DD_ENV= REPORT_EXIT_STATUS=1 TEST_PHP_SRCDIR=$(PROJ
 
 C_FILES = $(shell find components components-rs ext src/dogstatsd tracer zend_abstract_interface -name '*.c' -o -name '*.h' | awk '{ printf "$(BUILD_DIR)/%s\n", $$1 }' )
 TEST_FILES = $(shell find tests/ext -name '*.php*' -o -name '*.inc' -o -name '*.json' -o -name '*.yaml' -o -name 'CONFLICTS' | awk '{ printf "$(BUILD_DIR)/%s\n", $$1 }' )
-RUST_FILES = $(BUILD_DIR)/Cargo.toml $(BUILD_DIR)/Cargo.lock $(shell find components-rs -name '*.c' -o -name '*.rs' -o -name 'Cargo.toml' | awk '{ printf "$(BUILD_DIR)/%s\n", $$1 }' ) $(shell find libdatadog/{build-common,datadog-ffe,datadog-ipc,datadog-ipc-macros,datadog-live-debugger,datadog-live-debugger-ffi,datadog-remote-config,datadog-sidecar,datadog-sidecar-ffi,datadog-sidecar-macros,libdd-alloc,libdd-capabilities,libdd-capabilities-impl,libdd-common,libdd-common-ffi,libdd-crashtracker,libdd-crashtracker-ffi,libdd-data-pipeline,libdd-ddsketch,libdd-dogstatsd-client,libdd-library-config,libdd-library-config-ffi,libdd-log,libdd-shared-runtime,libdd-telemetry,libdd-telemetry-ffi,libdd-tinybytes,libdd-trace-*,spawn_worker,tools/{cc_utils,sidecar_mockgen},libdd-trace-*,Cargo.toml} \( -type l -o -type f \) \( -path "*/src*" -o -path "*/examples*" -o -path "*Cargo.toml" -o -path "*/build.rs" -o -path "*/tests/dataservice.rs" -o -path "*/tests/service_functional.rs" \) -not -path "*/datadog-ipc/build.rs" -not -path "*/datadog-sidecar-ffi/build.rs")
+RUST_FILES = $(BUILD_DIR)/Cargo.toml $(BUILD_DIR)/Cargo.lock $(shell find components-rs -name '*.c' -o -name '*.rs' -o -name 'Cargo.toml' | awk '{ printf "$(BUILD_DIR)/%s\n", $$1 }' ) $(shell find libdatadog/{build-common,datadog-ffe,datadog-ipc,datadog-ipc-macros,datadog-live-debugger,datadog-live-debugger-ffi,datadog-remote-config,datadog-sidecar,datadog-sidecar-ffi,datadog-sidecar-macros,libdd-alloc,libdd-capabilities,libdd-capabilities-impl,libdd-common,libdd-common-ffi,libdd-crashtracker,libdd-crashtracker-ffi,libdd-data-pipeline,libdd-ddsketch,libdd-dogstatsd-client,libdd-library-config,libdd-library-config-ffi,libdd-log,libdd-otel-thread-ctx*,libdd-shared-runtime,libdd-telemetry,libdd-telemetry-ffi,libdd-tinybytes,libdd-trace-*,spawn_worker,tools/{cc_utils,sidecar_mockgen},libdd-trace-*,Cargo.toml} \( -type l -o -type f \) \( -path "*/src*" -o -path "*/examples*" -o -path "*Cargo.toml" -o -path "*/build.rs" -o -path "*/tests/dataservice.rs" -o -path "*/tests/service_functional.rs" \) -not -path "*/datadog-ipc/build.rs" -not -path "*/datadog-sidecar-ffi/build.rs")
 ALL_OBJECT_FILES = $(C_FILES) $(RUST_FILES) $(BUILD_DIR)/Makefile
 TEST_OPCACHE_FILES = $(shell find tests/opcache -name '*.php*' -o -name '.gitkeep' | awk '{ printf "$(BUILD_DIR)/%s\n", $$1 }' )
 TEST_STUB_FILES = $(shell find tests/ext -type d -name 'stubs' -exec find '{}' -type f \; | awk '{ printf "$(BUILD_DIR)/%s\n", $$1 }' )
@@ -423,9 +423,9 @@ clang_format_fix:
 cbindgen: remove_cbindgen generate_cbindgen
 
 remove_cbindgen:
-	rm -f components-rs/datadog.h components-rs/live-debugger.h components-rs/telemetry.h components-rs/sidecar.h components-rs/common.h components-rs/crashtracker.h components-rs/library-config.h
+	rm -f components-rs/datadog.h components-rs/live-debugger.h components-rs/telemetry.h components-rs/sidecar.h components-rs/common.h components-rs/crashtracker.h components-rs/library-config.h components-rs/otel-thread-ctx.h
 
-generate_cbindgen: cbindgen_binary # Regenerate components-rs/datadog.h components-rs/live-debugger.h components-rs/telemetry.h components-rs/sidecar.h components-rs/common.h components-rs/crashtracker.h components-rs/library-config.h
+generate_cbindgen: cbindgen_binary # Regenerate components-rs/datadog.h components-rs/live-debugger.h components-rs/telemetry.h components-rs/sidecar.h components-rs/common.h components-rs/crashtracker.h components-rs/library-config.h components-rs/otel-thread-ctx.h
 	( \
 		$(command rustup && echo run nightly --) cbindgen --crate datadog-php  \
 			--config cbindgen.toml \
@@ -449,11 +449,14 @@ generate_cbindgen: cbindgen_binary # Regenerate components-rs/datadog.h componen
 		$(command rustup && echo run nightly --) cbindgen --crate libdd-library-config-ffi  \
 			--config libdd-library-config-ffi/cbindgen.toml \
 			--output $(PROJECT_ROOT)/components-rs/library-config.h; \
+		$(command rustup && echo run nightly --) cbindgen --crate libdd-otel-thread-ctx-ffi  \
+			--config libdd-otel-thread-ctx-ffi/cbindgen.toml \
+			--output $(PROJECT_ROOT)/components-rs/otel-thread-ctx.h; \
 		if test -d $(PROJECT_ROOT)/tmp; then \
 			mkdir -pv "$(BUILD_DIR)"; \
 			export CARGO_TARGET_DIR="$(BUILD_DIR)/target"; \
 		fi; \
-		cargo run -p tools --bin dedup_headers -- $(PROJECT_ROOT)/components-rs/common.h $(PROJECT_ROOT)/components-rs/datadog.h $(PROJECT_ROOT)/components-rs/live-debugger.h $(PROJECT_ROOT)/components-rs/telemetry.h $(PROJECT_ROOT)/components-rs/sidecar.h $(PROJECT_ROOT)/components-rs/crashtracker.h $(PROJECT_ROOT)/components-rs/library-config.h \
+		cargo run -p tools --bin dedup_headers -- $(PROJECT_ROOT)/components-rs/common.h $(PROJECT_ROOT)/components-rs/datadog.h $(PROJECT_ROOT)/components-rs/live-debugger.h $(PROJECT_ROOT)/components-rs/telemetry.h $(PROJECT_ROOT)/components-rs/sidecar.h $(PROJECT_ROOT)/components-rs/crashtracker.h $(PROJECT_ROOT)/components-rs/library-config.h $(PROJECT_ROOT)/components-rs/otel-thread-ctx.h \
 	)
 
 cbindgen_binary:

components-rs/Cargo.toml

@@ -54,6 +54,9 @@ libc = "0.2"
 bincode = { version = "1.3.3" }
 hashbrown = "0.15"
 
+[target.'cfg(target_os = "linux")'.dependencies]
+libdd-otel-thread-ctx-ffi = { path = "../libdatadog/libdd-otel-thread-ctx-ffi", default-features = false }
+
 [build-dependencies]
 cbindgen = "0.27"
 

components-rs/lib.rs

@@ -13,25 +13,29 @@ pub mod telemetry;
 pub mod trace_filter;
 pub mod bytes;
 
-use libdd_common::entity_id::{get_container_id, set_cgroup_file};
+pub use datadog_sidecar_ffi::*;
+pub use libdd_crashtracker_ffi::*;
+pub use libdd_common_ffi::*;
+pub use libdd_library_config_ffi::*;
+pub use libdd_telemetry_ffi::*;
+
 use http::uri::{PathAndQuery, Scheme};
 use http::Uri;
+use libdd_common::entity_id::{get_container_id, set_cgroup_file};
+use libdd_common::{parse_uri, Endpoint};
+use libdd_common_ffi::slice::AsBytes;
 use std::borrow::Cow;
 use std::ffi::{c_char, OsStr};
-#[cfg(unix)]
-use std::path::Path;
 use std::ptr::null_mut;
 use uuid::Uuid;
 
-pub use libdd_crashtracker_ffi::*;
-pub use libdd_library_config_ffi::*;
-pub use datadog_sidecar_ffi::*;
-use libdd_common::{parse_uri, Endpoint};
 #[cfg(unix)]
 use libdd_common::connector::uds::socket_path_to_uri;
-use libdd_common_ffi::slice::AsBytes;
-pub use libdd_common_ffi::*;
-pub use libdd_telemetry_ffi::*;
+#[cfg(unix)]
+use std::path::Path;
+
+#[cfg(target_os = "linux")]
+pub use libdd_otel_thread_ctx_ffi::*;
 
 #[no_mangle]
 #[allow(non_upper_case_globals)]

components-rs/otel-thread-ctx.h

@@ -0,0 +1,35 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+#ifndef DDOG_OTEL_THREAD_CTX_H
+#define DDOG_OTEL_THREAD_CTX_H
+
+#pragma once
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __linux__
+
+#define ddog_MAX_ATTRS_DATA_SIZE 612
+
+typedef struct ddog_ThreadContextHandle ddog_ThreadContextHandle;
+
+struct ddog_ThreadContextHandle *ddog_otel_thread_ctx_new(const uint8_t (*trace_id)[16],
+                                                          const uint8_t (*span_id)[8],
+                                                          const uint8_t (*local_root_span_id)[8]);
+
+void ddog_otel_thread_ctx_free(struct ddog_ThreadContextHandle *ctx);
+
+struct ddog_ThreadContextHandle *ddog_otel_thread_ctx_attach(struct ddog_ThreadContextHandle *ctx);
+
+struct ddog_ThreadContextHandle *ddog_otel_thread_ctx_detach(void);
+
+void ddog_otel_thread_ctx_update(const uint8_t (*trace_id)[16],
+                                 const uint8_t (*span_id)[8],
+                                 const uint8_t (*local_root_span_id)[8]);
+
+#endif
+
+#endif /* DDOG_OTEL_THREAD_CTX_H */

datadog.sym

@@ -1,6 +1,8 @@
 ddtrace_close_all_spans_and_flush
 datadog_get_formatted_session_id
 ddtrace_get_profiling_context
+ddtrace_get_profiling_otel_context
+otel_thread_ctx_v1
 ddtrace_get_root_span
 datadog_process_tags_get_serialized
 datadog_get_sidecar_queue_id

profiling/build.rs

@@ -270,6 +270,7 @@ fn generate_bindings(php_config_includes: &str, fibers: bool, zend_error_observe
         .raw_line("pub type zend_vm_opcode_handler_func_t = *const ::std::ffi::c_void;")
         // Block a few of functions that we'll provide defs for manually
         .blocklist_item("datadog_php_profiling_vm_interrupt_addr")
+        .blocklist_item("datadog_php_profiling_context_api_name")
         // I had to block these for some reason *shrug*
         .blocklist_item("FP_INFINITE")
         .blocklist_item("FP_INT_DOWNWARD")

profiling/src/bindings/mod.rs

@@ -340,6 +340,9 @@ extern "C" {
     /// Must be called from a PHP thread during a request.
     pub fn datadog_php_profiling_vm_interrupt_addr() -> *const AtomicBool;
 
+    /// Returns the ddtrace profiling context API selected during startup.
+    pub fn datadog_php_profiling_context_api_name() -> ZaiStr<'static>;
+
     /// Registers the extension. Note that it's kept in a zend_llist and gets
     /// pemalloc'd + memcpy'd into place. The engine says this is a mutable
     /// pointer, but in practice it's const.

profiling/src/lib.rs

@@ -648,6 +648,13 @@ extern "C" fn rinit(_type: c_int, _module_number: c_int) -> ZendResult {
     let once = unsafe { &*ptr::addr_of!(RINIT_ONCE) };
     once.call_once(|| {
         if system_settings.profiling_enabled {
+            // SAFETY: this returns a view of a static string owned by php_ffi.c.
+            let context_api = unsafe { bindings::datadog_php_profiling_context_api_name() };
+            info!(
+                "Profiling context API selected: {}.",
+                context_api.to_string_lossy()
+            );
+
             // SAFETY: sapi_module is initialized by rinit and shouldn't be
             // modified at this point (safe to read values).
             let sapi_module = unsafe { &*ptr::addr_of!(zend::sapi_module) };

profiling/src/php_ffi.c

@@ -15,16 +15,31 @@ const char *datadog_extension_build_id(void) { return ZEND_EXTENSION_BUILD_ID; }
 const char *datadog_module_build_id(void) { return ZEND_MODULE_BUILD_ID; }
 
 uint8_t *datadog_runtime_id = NULL;
+static const zai_str datadog_php_profiling_context_api_none = ZAI_STRL("none");
+static const zai_str datadog_php_profiling_context_api_otel = ZAI_STRL("ddtrace_get_profiling_otel_context");
+static const zai_str datadog_php_profiling_context_api_legacy = ZAI_STRL("ddtrace_get_profiling_context");
+static zai_str datadog_php_profiling_context_api = ZAI_STRL("none");
 
 static void locate_datadog_runtime_id(const zend_extension *extension) {
     datadog_runtime_id = DL_FETCH_SYMBOL(extension->handle, "datadog_runtime_id");
 }
 
 static void locate_ddtrace_get_profiling_context(const zend_extension *extension) {
+#ifdef __linux__
+    ddtrace_profiling_context (*get_profiling_otel)(void) =
+        DL_FETCH_SYMBOL(extension->handle, "ddtrace_get_profiling_otel_context");
+    if (EXPECTED(get_profiling_otel)) {
+        datadog_php_profiling_get_profiling_context = get_profiling_otel;
+        datadog_php_profiling_context_api = datadog_php_profiling_context_api_otel;
+        return;
+    }
+#endif
+
     ddtrace_profiling_context (*get_profiling)(void) =
         DL_FETCH_SYMBOL(extension->handle, "ddtrace_get_profiling_context");
     if (EXPECTED(get_profiling)) {
         datadog_php_profiling_get_profiling_context = get_profiling;
+        datadog_php_profiling_context_api = datadog_php_profiling_context_api_legacy;
     }
 }
 
@@ -153,6 +168,7 @@ void datadog_php_profiling_startup(zend_extension *extension) {
 
     datadog_php_profiling_get_profiling_context = noop_get_profiling_context;
     datadog_php_profiling_get_process_tags_serialized = noop_get_process_tags_serialized;
+    datadog_php_profiling_context_api = datadog_php_profiling_context_api_none;
 
     /* Due to the optional dependency on ddtrace, the profiling module will be
      * loaded after ddtrace if it's present, so ddtrace should always be found
@@ -177,6 +193,10 @@ void datadog_php_profiling_startup(zend_extension *extension) {
 #endif
 }
 
+zai_str datadog_php_profiling_context_api_name(void) {
+    return datadog_php_profiling_context_api;
+}
+
 void *datadog_php_profiling_vm_interrupt_addr(void) { return &EG(vm_interrupt); }
 
 zend_module_entry *datadog_get_module_entry(const char *str, uintptr_t len) {

profiling/src/php_ffi.h

@@ -83,8 +83,9 @@ typedef struct ddtrace_profiling_context_s {
 } ddtrace_profiling_context;
 
 /**
- * A pointer to the tracer's ddtrace_get_profiling_context function if it was
- * found, otherwise points to a function which just returns {0, 0}.
+ * A pointer to the tracer's profiling-context function if it was found,
+ * otherwise points to a function which just returns {0, 0}. On Linux this
+ * prefers ddtrace_get_profiling_otel_context when available.
  */
 extern ddtrace_profiling_context (*datadog_php_profiling_get_profiling_context)(void);
 
@@ -101,6 +102,12 @@ extern zend_string *(*datadog_php_profiling_get_process_tags_serialized)(void);
  */
 void datadog_php_profiling_startup(zend_extension *extension);
 
+/**
+ * Returns the ddtrace profiling context API selected during zend_extension
+ * startup, or "none" when no provider was found.
+ */
+zai_str datadog_php_profiling_context_api_name(void);
+
 /**
  * Used to hold information for overwriting the internal function handler
  * pointer in the Zend Engine.

tracer/ddtrace.c

@@ -57,6 +57,7 @@
 #include "live_debugger.h"
 #include "standalone_limiter.h"
 #include "priority_sampling/priority_sampling.h"
+#include "profiling.h"
 #include "random.h"
 #include "autoload_php_files.h"
 #include "serializer.h"
@@ -608,6 +609,7 @@ void ddtrace_rshutdown(bool fast_shutdown) {
             OBJ_RELEASE(&DDTRACE_G(active_stack)->std);
         }
         DDTRACE_G(active_stack) = NULL;
+        ddtrace_detach_otel_thread_context();
     }
 
     ddtrace_ffe_flush_exposures();
@@ -656,6 +658,7 @@ bool datadog_alter_dd_trace_disabled_config(zval *old_value, zval *new_value, ze
     } else if (!datadog_disable) {  // if this is true, the request has not been initialized at all
         ddtrace_close_all_open_spans(false);  // All remaining userland spans (and root span)
         dd_clean_globals();
+        ddtrace_detach_otel_thread_context();
     }
 
     return true;

tracer/handlers_fiber.c

@@ -1,6 +1,7 @@
 #include "ddtrace.h"
 #include "configuration.h"
 #include "handlers_fiber.h"
+#include "profiling.h"
 #include "span.h"
 #include <Zend/zend_extensions.h>
 #include <Zend/zend_observer.h>
@@ -130,6 +131,7 @@ static void dd_observe_fiber_switch(zend_fiber_context *from, zend_fiber_context
 
     from->reserved[dd_resource_handle] = DDTRACE_G(active_stack);
     DDTRACE_G(active_stack) = to_stack;
+    ddtrace_update_otel_thread_context();
 }
 
 static void dd_observe_fiber_init(zend_fiber_context *context) {