Fix crash when the loader is loaded multiple times

loader/dd_library_loader.c

@@ -23,6 +23,8 @@ static unsigned int php_api_no = 0;
 static const char *runtime_version = "unknown";
 static bool injection_forced = false;
 
+static bool already_done = false;
+
 #if defined(__MUSL__)
 # define OS_PATH "linux-musl/"
 #else
@@ -554,6 +556,7 @@ static int ddloader_load_extension(unsigned int php_api_no, char *module_build_i
     config->module_number = module_entry->module_number;
     config->version = (char *)module_entry->version;
 
+    LOG(INFO, "Extension '%s' loaded", config->ext_name);
     goto ok;
 
 abort_and_unload:
@@ -617,6 +620,11 @@ static int ddloader_api_no_check(int api_no) {
         return SUCCESS;
     }
 
+    if (already_done) {
+        LOG(WARN, "dd_library_loader has been loaded multiple times, aborting");
+        return SUCCESS;
+    }
+
     ddloader_configure();
 
     switch (api_no) {
@@ -687,10 +695,12 @@ static int ddloader_api_no_check(int api_no) {
 
 static int ddloader_build_id_check(const char *build_id) {
     // Guardrail
-    if (!ddloader_libc_check() || !php_api_no) {
+    if (!ddloader_libc_check() || !php_api_no || already_done) {
         return SUCCESS;
     }
 
+    already_done = true;
+
     bool is_zts = (strstr(build_id, "NTS") == NULL);
     bool is_debug = (strstr(build_id, "debug") != NULL);
 

loader/tests/functional/test_load_loader_multiple_times.php

@@ -0,0 +1,11 @@
+<?php
+
+require_once __DIR__."/includes/autoload.php";
+skip_if_php5();
+
+$output = runCLI('-dzend_extension='.getLoaderAbsolutePath().' '.__DIR__.'/fixtures/ddtrace.php', true, ['DD_TRACE_DEBUG=1']);
+
+// PHP warning
+assertContains($output, 'Cannot load dd_library_loader');
+// dd_library_loader warning
+assertContains($output, 'dd_library_loader has been loaded multiple times, aborting');