Fix compatilibity with PHP 5

Previous build could be loaded with php:5.6 docker image and I believe on centos 7 also.
But on ubuntu:22.04, there were issues like "undefined symbol: __zend_malloc".

This PR fixes this.

loader/compat_php.c

@@ -9,9 +9,11 @@
 #define PHP_70_71_72_IS_STR_INTERNED (1 << 1)
 
 ZEND_API zval *ZEND_FASTCALL zend_hash_set_bucket_key(HashTable *ht, Bucket *b, zend_string *key) __attribute__((weak));
-
 ZEND_API zval *ZEND_FASTCALL zend_hash_update(HashTable *ht, zend_string *key, zval *pData) __attribute__((weak));
 ZEND_API zval *ZEND_FASTCALL _zend_hash_update(HashTable *ht, zend_string *key, zval *pData) __attribute__((weak));
+ZEND_API zend_result ZEND_FASTCALL zend_hash_str_del(HashTable *ht, const char *str, size_t len) __attribute__((weak));
+ZEND_API zval* ZEND_FASTCALL zend_hash_str_find(const HashTable *ht, const char *key, size_t len) __attribute__((weak));
+ZEND_API void * __zend_malloc(size_t len) __attribute__((weak));
 
 static bool ddloader_zstr_is_interned(int php_api_no, zend_string *key) {
     if (php_api_no <= 20170718) {  // PHP 7.0 - 7.2
@@ -66,6 +68,29 @@ void ddloader_zend_string_release(int php_api_no, zend_string *s) {
     zend_string_release(s);
 }
 
+void *ddloader_zend_hash_str_find_ptr(int php_api_no, const HashTable *ht, const char *str, size_t len) {
+    UNUSED(php_api_no);
+    zval *zv;
+
+    if (!zend_hash_str_find) {
+        return NULL;
+    }
+
+    zv = zend_hash_str_find(ht, str, len);
+    if (zv) {
+        return Z_PTR_P(zv);
+    } else {
+        return NULL;
+    }
+}
+
+void ddloader_zend_hash_str_del(int php_api_no, HashTable *ht, const char *str, size_t len) {
+    UNUSED(php_api_no);
+    if (zend_hash_str_del) {
+        zend_hash_str_del(ht, str, len);
+    }
+}
+
 // This is an adaptation of zend_hash_set_bucket_key which is only available only starting from PHP 7.4
 // to be compatible with PHP 7.0+
 zval *ddloader_zend_hash_set_bucket_key(int php_api_no, HashTable *ht, Bucket *b, zend_string *key) {

loader/compat_php.h

@@ -7,6 +7,8 @@ zend_string *ddloader_zend_string_alloc(int php_api_no, size_t len, int persiste
 zend_string *ddloader_zend_string_init(int php_api_no, const char *str, size_t len, bool persistent);
 void ddloader_zend_string_release(int php_api_no, zend_string *s);
 zval *ddloader_zend_hash_set_bucket_key(int php_api_no, HashTable *ht, Bucket *b, zend_string *key);
+void *ddloader_zend_hash_str_find_ptr(int php_api_no, const HashTable *ht, const char *str, size_t len);
+void ddloader_zend_hash_str_del(int php_api_no, HashTable *ht, const char *str, size_t len);
 void ddloader_replace_zend_error_cb(int php_api_no);
 void ddloader_restore_zend_error_cb();
 zval *ddloader_zend_hash_update(HashTable *ht, zend_string *key, zval *pData);

loader/dd_library_loader.c

@@ -64,7 +64,7 @@ static char *ddtrace_pre_load_hook(void) {
 }
 
 static bool ddloader_is_ext_loaded(const char *name) {
-    return zend_hash_str_find_ptr(&module_registry, name, strlen(name))
+    return ddloader_zend_hash_str_find_ptr(php_api_no, &module_registry, name, strlen(name))
         || zend_get_extension(name)
     ;
 }
@@ -390,14 +390,14 @@ static bool ddloader_check_deps(const zend_module_dep *deps) {
 }
 
 static void ddloader_unregister_module(const char *name) {
-    zend_module_entry *injected = zend_hash_str_find_ptr(&module_registry, name, strlen(name));
+    zend_module_entry *injected = ddloader_zend_hash_str_find_ptr(php_api_no, &module_registry, name, strlen(name));
     if (!injected) {
         return;
     }
 
     // Set the MSHUTDOWN function to NULL to avoid it being called by zend_hash_str_del
     injected->module_shutdown_func = NULL;
-    zend_hash_str_del(&module_registry, name, strlen(name));
+    ddloader_zend_hash_str_del(php_api_no, &module_registry, name, strlen(name));
 }
 
 static PHP_MINIT_FUNCTION(ddloader_injected_extension_minit) {
@@ -414,7 +414,7 @@ static PHP_MINIT_FUNCTION(ddloader_injected_extension_minit) {
         return SUCCESS;
     }
 
-    zend_module_entry *module = zend_hash_str_find_ptr(&module_registry, config->ext_name, strlen(config->ext_name));
+    zend_module_entry *module = ddloader_zend_hash_str_find_ptr(php_api_no, &module_registry, config->ext_name, strlen(config->ext_name));
     if (module) {
         LOG(INFO, "Extension '%s' is already loaded, unregister the injected extension", config->ext_name);
         ddloader_unregister_module(config->tmp_name);
@@ -446,7 +446,7 @@ static PHP_MINIT_FUNCTION(ddloader_injected_extension_minit) {
     ddloader_zend_hash_set_bucket_key(php_api_no, &module_registry, bucket, new_name);
     ddloader_zend_string_release(php_api_no, new_name);
 
-    module = zend_hash_str_find_ptr(&module_registry, config->ext_name, strlen(config->ext_name));
+    module = ddloader_zend_hash_str_find_ptr(php_api_no, &module_registry, config->ext_name, strlen(config->ext_name));
     if (!module) {
         TELEMETRY(REASON_ERROR, "Extension '%s' not found after renaming. Something wrong happened", config->ext_name);
         return SUCCESS;