feat(prof): use a trampoline for FLF functions to intercept timings

profiling/Cargo.toml

@@ -22,6 +22,7 @@ cfg-if = { version = "1.0" }
 cpu-time = { version = "1.0" }
 chrono = { version = "0.4" }
 crossbeam-channel = { version = "0.5", default-features = false, features = ["std"] }
+dynasmrt = "2.0"
 http = { version = "1.4" }
 libdd-alloc = {  git = "https://github.com/DataDog/libdatadog", tag = "v29.0.0" }
 libdd-profiling = {  git = "https://github.com/DataDog/libdatadog", tag = "v29.0.0" }

profiling/build.rs

@@ -36,6 +36,7 @@ fn main() {
     let post_startup_cb = cfg_post_startup_cb(vernum);
     let preload = cfg_preload(vernum);
     let fibers = cfg_fibers(vernum);
+    let frameless = cfg_frameless(vernum);
     let run_time_cache = cfg_run_time_cache(vernum);
     let trigger_time_sample = cfg_trigger_time_sample();
     let zend_error_observer = cfg_zend_error_observer(vernum);
@@ -47,6 +48,7 @@ fn main() {
         preload,
         run_time_cache,
         fibers,
+        frameless,
         trigger_time_sample,
         zend_error_observer,
     );
@@ -103,6 +105,7 @@ fn build_zend_php_ffis(
     preload: bool,
     run_time_cache: bool,
     fibers: bool,
+    frameless: bool,
     trigger_time_sample: bool,
     zend_error_observer: bool,
 ) {
@@ -143,6 +146,7 @@ fn build_zend_php_ffis(
     let post_startup_cb = if post_startup_cb { "1" } else { "0" };
     let preload = if preload { "1" } else { "0" };
     let fibers = if fibers { "1" } else { "0" };
+    let frameless = if frameless { "1" } else { "0" };
     let run_time_cache = if run_time_cache { "1" } else { "0" };
     let trigger_time_sample = if trigger_time_sample { "1" } else { "0" };
     let zend_error_observer = if zend_error_observer { "1" } else { "0" };
@@ -159,6 +163,7 @@ fn build_zend_php_ffis(
         .define("CFG_POST_STARTUP_CB", post_startup_cb)
         .define("CFG_PRELOAD", preload)
         .define("CFG_FIBERS", fibers)
+        .define("CFG_FRAMELESS", frameless)
         .define("CFG_RUN_TIME_CACHE", run_time_cache)
         .define("CFG_STACK_WALKING_TESTS", stack_walking_tests)
         .define("CFG_TRIGGER_TIME_SAMPLE", trigger_time_sample)
@@ -373,6 +378,16 @@ fn cfg_fibers(vernum: u64) -> bool {
     }
 }
 
+fn cfg_frameless(vernum: u64) -> bool {
+    println!("cargo::rustc-check-cfg=cfg(php_frameless)");
+    if vernum >= 80400 {
+        println!("cargo:rustc-cfg=php_frameless");
+        true
+    } else {
+        false
+    }
+}
+
 fn cfg_php_feature_flags(vernum: u64) {
     println!("cargo::rustc-check-cfg=cfg(php_gc_status, php_zend_compile_string_has_position, php_gc_status_extended, php_frameless, php_opcache_restart_hook, php_zend_mm_set_custom_handlers_ex)");
 
@@ -386,7 +401,6 @@ fn cfg_php_feature_flags(vernum: u64) {
         println!("cargo:rustc-cfg=php_gc_status_extended");
     }
     if vernum >= 80400 {
-        println!("cargo:rustc-cfg=php_frameless");
         println!("cargo:rustc-cfg=php_opcache_restart_hook");
         println!("cargo:rustc-cfg=php_zend_mm_set_custom_handlers_ex");
     }

profiling/src/php_ffi.c

@@ -121,6 +121,10 @@ bool ddog_php_prof_is_post_startup(void) {
 static post_startup_cb_result (*orig_post_startup_cb)(void) = NULL;
 
 static post_startup_cb_result ddog_php_prof_post_startup_cb(void) {
+#if CFG_FRAMELESS
+    ddog_php_prof_post_startup(); // before preload+JIT (which may hardcode the flf handlers)
+#endif
+
     if (orig_post_startup_cb) {
         post_startup_cb_result (*cb)(void) = orig_post_startup_cb;
 
@@ -552,9 +556,6 @@ void ddog_php_test_free_fake_zend_function(zend_function *func) {
     free(func);
 }
 
-// Stub for zend_flf_functions (PHP 8.4+ frameless calls) to allow tests to link
-// without the real PHP runtime. The test doesn't exercise frameless code paths.
-__attribute__((weak)) zend_function **zend_flf_functions;
 #endif // CFG_STACK_WALKING_TESTS || CFG_TEST
 
 void *opcache_handle = NULL;

profiling/src/php_ffi.h

@@ -153,6 +153,10 @@ void ddog_php_prof_zend_mm_set_custom_handlers(zend_mm_heap *heap,
 
 zend_execute_data* ddog_php_prof_get_current_execute_data();
 
+#if CFG_FRAMELESS
+void ddog_php_prof_post_startup();
+#endif
+
 #if CFG_FIBERS
 zend_fiber* ddog_php_prof_get_active_fiber();
 zend_fiber* ddog_php_prof_get_active_fiber_test();