print backtrace in assert logging with libunwind

From: Stefan Bühler <stbuehler@web.de>

git-svn-id: svn://svn.lighttpd.net/lighttpd/branches/lighttpd-1.4.x@2974 152afb58-edef-0310-8abb-c4023f1b3aa9

NEWS

@@ -14,6 +14,7 @@ NEWS
   * fixed typo in example config found by openSUSE user (boo# 907709)
   * [network] fix compile break in calculation of sockaddr_un size if SUN_LEN is not defined (fixes #2609)
   * [connections] fix bug in connection state handling
+  * print backtrace in assert logging with libunwind
 
 - 1.4.35 - 2014-03-12
   * [network/ssl] fix build error if TLSEXT is disabled

configure.ac

@@ -285,6 +285,17 @@ if test "$WITH_VALGRIND" != "no"; then
  AC_CHECK_HEADERS([valgrind/valgrind.h])
 fi
 
+dnl Checking for libunwind
+AC_MSG_CHECKING(for libunwind)
+AC_ARG_WITH(libunwind,
+    AC_HELP_STRING([--with-libunwind],[Include libunwind support for backtraces on assert failures]),
+    [WITH_LIBUNWIND=$withval],[WITH_LIBUNWIND=no])
+
+if test "$WITH_LIBUNWIND" != "no"; then
+  PKG_CHECK_MODULES(LIBUNWIND, libunwind)
+  AC_DEFINE(HAVE_LIBUNWIND, 1, [Have libunwind support])
+fi
+
 dnl Check for openssl
 AC_MSG_CHECKING(for OpenSSL)
 AC_ARG_WITH(openssl,

src/CMakeLists.txt

@@ -29,6 +29,7 @@ OPTION(WITH_FAM "fam/gamin for reducing number of stat() calls [default: off]")
 OPTION(WITH_GDBM "gdbm storage for mod_trigger_b4_dl [default: off]")
 OPTION(WITH_MEMCACHE "memcached storage for mod_trigger_b4_dl [default: off]")
 OPTION(WITH_LIBEV "libev support for fdevent handlers [default: off]")
+OPTION(WITH_LIBUNWIND "with libunwind to print backtraces in asserts [default: off]")
 
 IF(CMAKE_COMPILER_IS_GNUCC)
 	OPTION(BUILD_EXTRA_WARNINGS "extra warnings")
@@ -54,6 +55,11 @@ IF(WITH_LIBEV)
   SET(HAVE_LIBEV 1 FORCE)
 ENDIF(WITH_LIBEV)
 
+IF(WITH_LIBUNWIND)
+  pkg_check_modules(LIBUNWIND REQUIRED libunwind)
+  SET(HAVE_LIBUNWIND 1 FORCE)
+ENDIF()
+
 IF(WITH_WEBDAV_PROPS)
   SET(WITH_XML 1)
   SET(WITH_SQLITE3 1)
@@ -610,6 +616,11 @@ IF(WITH_LIBEV)
   ADD_TARGET_PROPERTIES(lighttpd COMPILE_FLAGS ${LIBEV_CFLAGS})
 ENDIF(WITH_LIBEV)
 
+IF(WITH_LIBUNWIND)
+  TARGET_LINK_LIBRARIES(lighttpd ${LIBUNWIND_LDFLAGS})
+  ADD_TARGET_PROPERTIES(lighttpd COMPILE_FLAGS ${LIBUNWIND_CFLAGS})
+ENDIF()
+
 IF(NOT WIN32)
 INSTALL(TARGETS ${L_INSTALL_TARGETS}
 	RUNTIME DESTINATION ${SBINDIR}

src/Makefile.am

@@ -1,4 +1,4 @@
-AM_CFLAGS = $(FAM_CFLAGS)
+AM_CFLAGS = $(FAM_CFLAGS) $(LIBUNWIND_CFLAGS)
 
 noinst_PROGRAMS=proc_open lemon # simple-fcgi #graphic evalo bench ajp ssl error_test adserver gen-license
 sbin_PROGRAMS=lighttpd lighttpd-angel
@@ -284,11 +284,12 @@ hdr = server.h buffer.h network.h log.h keyvalue.h \
 DEFS= @DEFS@ -DHAVE_VERSION_H -DLIBRARY_DIR="\"$(libdir)\"" -DSBIN_DIR="\"$(sbindir)\""
 
 lighttpd_SOURCES = $(src)
-lighttpd_LDADD = $(PCRE_LIB) $(DL_LIB) $(SENDFILE_LIB) $(ATTR_LIB) $(common_libadd) $(SSL_LIB) $(FAM_LIBS) $(LIBEV_LIBS)
+lighttpd_LDADD = $(PCRE_LIB) $(DL_LIB) $(SENDFILE_LIB) $(ATTR_LIB) $(common_libadd) $(SSL_LIB) $(FAM_LIBS) $(LIBEV_LIBS) $(LIBUNWIND_LIBS)
 lighttpd_LDFLAGS = -export-dynamic
 lighttpd_CCPFLAGS = $(FAM_CFLAGS) $(LIBEV_CFLAGS)
 
 proc_open_SOURCES = proc_open.c buffer.c
+proc_open_LDADD = $(LIBUNWIND_LIBS)
 proc_open_CPPFLAGS= -DDEBUG_PROC_OPEN
 
 #gen_license_SOURCES = license.c md5.c buffer.c gen_license.c

src/buffer.c

@@ -1059,9 +1059,80 @@ int buffer_to_upper(buffer *b) {
 	return 0;
 }
 
+#ifdef HAVE_LIBUNWIND
+# define UNW_LOCAL_ONLY
+# include <libunwind.h>
+
+void print_backtrace(FILE *file) {
+	unw_cursor_t cursor;
+	unw_context_t context;
+	int ret;
+	unsigned int frame = 0;
+
+	if (0 != (ret = unw_getcontext(&context))) goto error;
+	if (0 != (ret = unw_init_local(&cursor, &context))) goto error;
+
+	fprintf(file, "Backtrace:\n");
+
+	while (0 < (ret = unw_step(&cursor))) {
+		unw_word_t proc_ip = 0;
+		unw_proc_info_t procinfo;
+		char procname[256];
+		unw_word_t proc_offset = 0;
+
+		if (0 != (ret = unw_get_reg(&cursor, UNW_REG_IP, &proc_ip))) goto error;
+
+		if (0 == proc_ip) {
+			/* without an IP the other functions are useless; unw_get_proc_name would return UNW_EUNSPEC */
+			++frame;
+			fprintf(file, "%u: (nil)\n", frame);
+			continue;
+		}
+
+		if (0 != (ret = unw_get_proc_info(&cursor, &procinfo))) goto error;
+
+		if (0 != (ret = unw_get_proc_name(&cursor, procname, sizeof(procname), &proc_offset))) {
+			switch (-ret) {
+			case UNW_ENOMEM:
+				memset(procname + sizeof(procname) - 4, '.', 3);
+				procname[sizeof(procname) - 1] = '\0';
+				break;
+			case UNW_ENOINFO:
+				procname[0] = '?';
+				procname[1] = '\0';
+				proc_offset = 0;
+				break;
+			default:
+				snprintf(procname, sizeof(procname), "?? (unw_get_proc_name error %d)", -ret);
+				break;
+			}
+		}
+
+		++frame;
+		fprintf(file, "%u: %s (+0x%x) [%p]\n",
+			frame,
+			procname,
+			(unsigned int) proc_offset,
+			(void*)(uintptr_t)proc_ip);
+	}
+
+	if (0 != ret) goto error;
+
+	return;
+
+error:
+	fprintf(file, "Error while generating backtrace: unwind error %i\n", (int) -ret);
+}
+#else
+void print_backtrace(FILE *file) {
+	UNUSED(file);
+}
+#endif
+
 void log_failed_assert(const char *filename, unsigned int line, const char *msg) {
 	/* can't use buffer here; could lead to recursive assertions */
 	fprintf(stderr, "%s.%d: %s\n", filename, line, msg);
+	print_backtrace(stderr);
 	fflush(stderr);
 	abort();
 }

src/buffer.h

@@ -9,6 +9,7 @@
 
 #include <stdlib.h>
 #include <sys/types.h>
+#include <stdio.h>
 
 typedef struct {
 	char *ptr;
@@ -128,6 +129,7 @@ int light_isalnum(int c);
 
 #define UNUSED(x) ( (void)(x) )
 
+void print_backtrace(FILE *file);
 void log_failed_assert(const char *filename, unsigned int line, const char *msg) LI_NORETURN;
 #define force_assert(x) do { if (!(x)) log_failed_assert(__FILE__, __LINE__, "assertion failed: " #x); } while(0)
 #define SEGFAULT() log_failed_assert(__FILE__, __LINE__, "aborted");

src/config.h.cmake

@@ -158,4 +158,7 @@
 /* libev */
 #cmakedefine HAVE_LIBEV
 
+/* libunwind */
+#cmakedefine HAVE_LIBUNWIND
+
 #cmakedefine LIGHTTPD_STATIC