rfc: error_backtraces_v2

This commit adds an INI setting, 'fatal_error_backtraces', which users
can enable or disable to control whether or not PHP produces backtraces
for fatal errors.

It defaults to enabled, meaning that any non-recoverable error will now
have a backtrace associated with it. For example, a script timeout will
now look like:

  Fatal error: Maximum execution time of 1 second exceeded in example.php on line 23
  Stack trace:
  #0 example.php(23): usleep(10000)
  php#1 example.php(24): recurse()
  php#2 example.php(24): recurse()
  ...

It respects the `zend.exception_ignore_args` INI setting and the
SensitiveParameter attributes, so users can ensure that sensitive
arguments do not end up in the backtrace.

Zend/tests/fatal_error_backtraces_001.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Fatal error backtrace
+--FILE--
+<?php
+
+ini_set('fatal_error_backtraces', true);
+
+$argv[1] = "stdClass";
+
+include __DIR__ . '/new_oom.inc';
+
+?>
+--EXPECTF--
+Fatal error: Allowed memory size of %d bytes exhausted at %s:%d (tried to allocate %d bytes) in %snew_oom.inc on line %d
+Stack trace:
+#0 %snew_oom.inc(%d): ReflectionClass->newInstanceWithoutConstructor()
+#1 %sfatal_error_backtraces_001.php(%d): include('%s')
+#2 {main}

Zend/tests/fatal_error_backtraces_002.phpt

@@ -0,0 +1,23 @@
+--TEST--
+Fatal error backtrace w/ sensitive parameters
+--FILE--
+<?php
+
+ini_set('fatal_error_backtraces', true);
+
+function oom(#[\SensitiveParameter] $unused) {
+    $argv[1] = "stdClass";
+
+    include __DIR__ . '/new_oom.inc';
+}
+
+oom("foo");
+
+?>
+--EXPECTF--
+Fatal error: Allowed memory size of %d bytes exhausted at %s:%d (tried to allocate %d bytes) in %snew_oom.inc on line %d
+Stack trace:
+#0 %snew_oom.inc(%d): ReflectionClass->newInstanceWithoutConstructor()
+#1 %sfatal_error_backtraces_002.php(%d): include(%s)
+#2 %sfatal_error_backtraces_002.php(%d): oom(Object(SensitiveParameterValue))
+#3 {main}

Zend/tests/fatal_error_backtraces_003.phpt

@@ -0,0 +1,24 @@
+--TEST--
+Fatal error backtrace w/ zend.exception_ignore_args
+--FILE--
+<?php
+
+ini_set('fatal_error_backtraces', true);
+ini_set('zend.exception_ignore_args', true);
+
+function oom($unused) {
+    $argv[1] = "stdClass";
+
+    include __DIR__ . '/new_oom.inc';
+}
+
+oom("foo");
+
+?>
+--EXPECTF--
+Fatal error: Allowed memory size of %d bytes exhausted at %s:%d (tried to allocate %d bytes) in %snew_oom.inc on line %d
+Stack trace:
+#0 %snew_oom.inc(%d): ReflectionClass->newInstanceWithoutConstructor()
+#1 %sfatal_error_backtraces_003.php(%d): include(%s)
+#2 %sfatal_error_backtraces_003.php(%d): oom()
+#3 {main}

Zend/zend.c

@@ -119,6 +119,13 @@ static ZEND_INI_MH(OnUpdateErrorReporting) /* {{{ */
 }
 /* }}} */
 
+static ZEND_INI_MH(OnUpdateFatalErrorBacktraces)
+{
+	EG(fatal_error_backtraces) = zend_ini_parse_bool(new_value);
+
+	return SUCCESS;
+}
+
 static ZEND_INI_MH(OnUpdateGCEnabled) /* {{{ */
 {
 	bool val;
@@ -260,6 +267,7 @@ static ZEND_INI_MH(OnUpdateFiberStackSize) /* {{{ */
 
 ZEND_INI_BEGIN()
 	ZEND_INI_ENTRY("error_reporting",				NULL,		ZEND_INI_ALL,		OnUpdateErrorReporting)
+	ZEND_INI_ENTRY("fatal_error_backtraces",			"1",		ZEND_INI_ALL,		OnUpdateFatalErrorBacktraces)
 	STD_ZEND_INI_ENTRY("zend.assertions",				"1",    ZEND_INI_ALL,       OnUpdateAssertions,           assertions,   zend_executor_globals,  executor_globals)
 	ZEND_INI_ENTRY3_EX("zend.enable_gc",				"1",	ZEND_INI_ALL,		OnUpdateGCEnabled, NULL, NULL, NULL, zend_gc_enabled_displayer_cb)
 	STD_ZEND_INI_BOOLEAN("zend.multibyte", "0", ZEND_INI_PERDIR, OnUpdateBool, multibyte,      zend_compiler_globals, compiler_globals)
@@ -811,6 +819,7 @@ static void executor_globals_ctor(zend_executor_globals *executor_globals) /* {{
 	executor_globals->in_autoload = NULL;
 	executor_globals->current_execute_data = NULL;
 	executor_globals->current_module = NULL;
+	ZVAL_UNDEF(&executor_globals->error_backtrace);
 	executor_globals->exit_status = 0;
 #if XPFPA_HAVE_CW
 	executor_globals->saved_fpu_cw = 0;
@@ -1048,6 +1057,7 @@ void zend_startup(zend_utility_functions *utility_functions) /* {{{ */
 	CG(map_ptr_size) = 0;
 	CG(map_ptr_last) = 0;
 #endif /* ZTS */
+
 	EG(error_reporting) = E_ALL & ~E_NOTICE;
 
 	zend_interned_strings_init();
@@ -1463,6 +1473,9 @@ ZEND_API ZEND_COLD void zend_error_zstr_at(
 		EG(errors)[EG(num_errors)-1] = info;
 	}
 
+	// Always clear the last backtrace.
+	zval_ptr_dtor(&EG(error_backtrace));
+
 	/* Report about uncaught exception in case of fatal errors */
 	if (EG(exception)) {
 		zend_execute_data *ex;
@@ -1484,6 +1497,8 @@ ZEND_API ZEND_COLD void zend_error_zstr_at(
 				ex->opline = opline;
 			}
 		}
+	} else if (EG(fatal_error_backtraces) && (type & E_FATAL_ERRORS)) {
+		zend_fetch_debug_backtrace(&EG(error_backtrace), 0, EG(exception_ignore_args) ? DEBUG_BACKTRACE_IGNORE_ARGS : 0, 0);
 	}
 
 	zend_observer_error_notify(type, error_filename, error_lineno, message);

Zend/zend_execute_API.c

@@ -307,6 +307,9 @@ ZEND_API void zend_shutdown_executor_values(bool fast_shutdown)
 			} ZEND_HASH_MAP_FOREACH_END_DEL();
 		}
 
+		zval_ptr_dtor(&EG(error_backtrace));
+		ZVAL_UNDEF(&EG(error_backtrace));
+
 		/* Release static properties and static variables prior to the final GC run,
 		 * as they may hold GC roots. */
 		ZEND_HASH_MAP_REVERSE_FOREACH_VAL(EG(function_table), zv) {

Zend/zend_globals.h

@@ -181,7 +181,11 @@ struct _zend_executor_globals {
 
 	JMP_BUF *bailout;
 
-	int error_reporting;
+	int  error_reporting;
+
+	int  fatal_error_backtraces;
+	zval error_backtrace;
+
 	int exit_status;
 
 	HashTable *function_table;	/* function symbol table */

ext/standard/basic_functions.c

@@ -1436,6 +1436,11 @@ PHP_FUNCTION(error_get_last)
 
 		ZVAL_LONG(&tmp, PG(last_error_lineno));
 		zend_hash_update(Z_ARR_P(return_value), ZSTR_KNOWN(ZEND_STR_LINE), &tmp);
+
+		if (!Z_ISUNDEF(EG(error_backtrace))) {
+			ZVAL_COPY(&tmp, &EG(error_backtrace));
+			zend_hash_update(Z_ARR_P(return_value), ZSTR_KNOWN(ZEND_STR_TRACE), &tmp);
+		}
 	}
 }
 /* }}} */
@@ -1457,6 +1462,9 @@ PHP_FUNCTION(error_clear_last)
 			PG(last_error_file) = NULL;
 		}
 	}
+
+	zval_ptr_dtor(&EG(error_backtrace));
+	ZVAL_UNDEF(&EG(error_backtrace));
 }
 /* }}} */
 

ext/standard/tests/general_functions/error_get_last.phpt

@@ -15,7 +15,18 @@ $a = $b;
 
 var_dump(error_get_last());
 
-echo "Done\n";
+function trigger_fatal_error_with_stacktrace() {
+    ini_set('fatal_error_backtraces', true);
+
+    eval("class Foo {}; class Foo {}");
+}
+
+register_shutdown_function(function() {
+    var_dump(error_get_last());
+    echo "Done\n";
+});
+
+trigger_fatal_error_with_stacktrace();
 ?>
 --EXPECTF--
 NULL
@@ -33,4 +44,44 @@ array(4) {
   ["line"]=>
   int(11)
 }
+
+Fatal error: Cannot redeclare class Foo (previously declared in /Users/enorris/workspace/php-src/ext/standard/tests/general_functions/error_get_last.php(18) : eval()'d code:1) in /Users/enorris/workspace/php-src/ext/standard/tests/general_functions/error_get_last.php(18) : eval()'d code on line 1
+Stack trace:
+#0 %serror_get_last.php(%d): eval()
+#1 %serror_get_last.php(%d): trigger_fatal_error_with_stacktrace()
+#2 {main}
+array(5) {
+  ["type"]=>
+  int(64)
+  ["message"]=>
+  string(%d) "Cannot redeclare class Foo %s"
+  ["file"]=>
+  string(%d) "%serror_get_last.php(%d) : eval()'d code"
+  ["line"]=>
+  int(%d)
+  ["trace"]=>
+  array(2) {
+    [0]=>
+    array(3) {
+      ["file"]=>
+      string(%d) "%serror_get_last.php"
+      ["line"]=>
+      int(%d)
+      ["function"]=>
+      string(%d) "eval"
+    }
+    [1]=>
+    array(4) {
+      ["file"]=>
+      string(%d) "%serror_get_last.php"
+      ["line"]=>
+      int(%d)
+      ["function"]=>
+      string(%d) "trigger_fatal_error_with_stacktrace"
+      ["args"]=>
+      array(0) {
+      }
+    }
+  }
+}
 Done

main/main.c

@@ -1282,6 +1282,7 @@ static ZEND_COLD void php_error_cb(int orig_type, zend_string *error_filename, c
 {
 	bool display;
 	int type = orig_type & E_ALL;
+	zend_string *backtrace = ZSTR_EMPTY_ALLOC();
 
 	/* check for repeated errors to be ignored */
 	if (PG(ignore_repeated_errors) && PG(last_error_message)) {
@@ -1321,6 +1322,10 @@ static ZEND_COLD void php_error_cb(int orig_type, zend_string *error_filename, c
 		}
 	}
 
+	if (!Z_ISUNDEF(EG(error_backtrace))) {
+		backtrace = zend_trace_to_string(Z_ARRVAL(EG(error_backtrace)), /* include_main */ true);
+	}
+
 	/* store the error if it has changed */
 	if (display) {
 		clear_last_error();
@@ -1389,14 +1394,14 @@ static ZEND_COLD void php_error_cb(int orig_type, zend_string *error_filename, c
 				syslog(LOG_ALERT, "PHP %s: %s (%s)", error_type_str, ZSTR_VAL(message), GetCommandLine());
 			}
 #endif
-			spprintf(&log_buffer, 0, "PHP %s:  %s in %s on line %" PRIu32, error_type_str, ZSTR_VAL(message), ZSTR_VAL(error_filename), error_lineno);
+			spprintf(&log_buffer, 0, "PHP %s:  %s in %s on line %" PRIu32 "%s%s", error_type_str, ZSTR_VAL(message), ZSTR_VAL(error_filename), error_lineno, ZSTR_LEN(backtrace) ? "\nStack trace:\n" : "", ZSTR_VAL(backtrace));
 			php_log_err_with_severity(log_buffer, syslog_type_int);
 			efree(log_buffer);
 		}
 
 		if (PG(display_errors) && ((module_initialized && !PG(during_request_startup)) || (PG(display_startup_errors)))) {
 			if (PG(xmlrpc_errors)) {
-				php_printf("<?xml version=\"1.0\"?><methodResponse><fault><value><struct><member><name>faultCode</name><value><int>" ZEND_LONG_FMT "</int></value></member><member><name>faultString</name><value><string>%s:%s in %s on line %" PRIu32 "</string></value></member></struct></value></fault></methodResponse>", PG(xmlrpc_error_number), error_type_str, ZSTR_VAL(message), ZSTR_VAL(error_filename), error_lineno);
+				php_printf("<?xml version=\"1.0\"?><methodResponse><fault><value><struct><member><name>faultCode</name><value><int>" ZEND_LONG_FMT "</int></value></member><member><name>faultString</name><value><string>%s:%s in %s on line %" PRIu32 "%s%s</string></value></member></struct></value></fault></methodResponse>", PG(xmlrpc_error_number), error_type_str, ZSTR_VAL(message), ZSTR_VAL(error_filename), error_lineno, ZSTR_LEN(backtrace) ? "\nStack trace:\n" : "", ZSTR_VAL(backtrace));
 			} else {
 				char *prepend_string = INI_STR("error_prepend_string");
 				char *append_string = INI_STR("error_append_string");
@@ -1407,7 +1412,7 @@ static ZEND_COLD void php_error_cb(int orig_type, zend_string *error_filename, c
 						php_printf("%s<br />\n<b>%s</b>:  %s in <b>%s</b> on line <b>%" PRIu32 "</b><br />\n%s", STR_PRINT(prepend_string), error_type_str, ZSTR_VAL(buf), ZSTR_VAL(error_filename), error_lineno, STR_PRINT(append_string));
 						zend_string_free(buf);
 					} else {
-						php_printf_unchecked("%s<br />\n<b>%s</b>:  %S in <b>%s</b> on line <b>%" PRIu32 "</b><br />\n%s", STR_PRINT(prepend_string), error_type_str, message, ZSTR_VAL(error_filename), error_lineno, STR_PRINT(append_string));
+						php_printf_unchecked("%s<br />\n<b>%s</b>:  %S in <b>%s</b> on line <b>%" PRIu32 "</b><br />%s%s\n%s", STR_PRINT(prepend_string), error_type_str, message, ZSTR_VAL(error_filename), error_lineno, ZSTR_LEN(backtrace) ? "\nStack trace:\n" : "", ZSTR_VAL(backtrace), STR_PRINT(append_string));
 					}
 				} else {
 					/* Write CLI/CGI errors to stderr if display_errors = "stderr" */
@@ -1416,18 +1421,20 @@ static ZEND_COLD void php_error_cb(int orig_type, zend_string *error_filename, c
 					) {
 						fprintf(stderr, "%s: ", error_type_str);
 						fwrite(ZSTR_VAL(message), sizeof(char), ZSTR_LEN(message), stderr);
-						fprintf(stderr, " in %s on line %" PRIu32 "\n", ZSTR_VAL(error_filename), error_lineno);
+						fprintf(stderr, " in %s on line %" PRIu32 "%s%s\n", ZSTR_VAL(error_filename), error_lineno, ZSTR_LEN(backtrace) ? "\nStack trace:\n" : "", ZSTR_VAL(backtrace));
 #ifdef PHP_WIN32
 						fflush(stderr);
 #endif
 					} else {
-						php_printf_unchecked("%s\n%s: %S in %s on line %" PRIu32 "\n%s", STR_PRINT(prepend_string), error_type_str, message, ZSTR_VAL(error_filename), error_lineno, STR_PRINT(append_string));
+						php_printf_unchecked("%s\n%s: %S in %s on line %" PRIu32 "%s%s\n%s", STR_PRINT(prepend_string), error_type_str, message, ZSTR_VAL(error_filename), error_lineno, ZSTR_LEN(backtrace) ? "\nStack trace:\n" : "", ZSTR_VAL(backtrace), STR_PRINT(append_string));
 					}
 				}
 			}
 		}
 	}
 
+	zend_string_release(backtrace);
+
 	/* Bail out if we can't recover */
 	switch (type) {
 		case E_CORE_ERROR:

run-tests.php

@@ -272,6 +272,7 @@ function main(): void
         'disable_functions=',
         'output_buffering=Off',
         'error_reporting=' . E_ALL,
+        'fatal_error_backtraces=Off',
         'display_errors=1',
         'display_startup_errors=1',
         'log_errors=0',