Basic backtrace ability

On platforms with the backtrace/backtrace_symbols_fd interface, Tor
can now dump stack traces on assertion failure.  By default, I log
them to DataDir/stack_dump and to stderr.

4 files changed, 177 insertions, 0 deletions

diff --git a/src/common/backtrace.c b/src/common/backtrace.c
new file mode 100644
index 000000000..d3f59b2c7
--- /dev/null
+++ b/src/common/backtrace.c
@@ -0,0 +1,157 @@
+/* Copyright (c) 2013, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#include "orconfig.h"
+#include "backtrace.h"
+#include "compat.h"
+#include "util.h"
+
+#ifdef HAVE_EXECINFO_H
+#include <execinfo.h>
+#endif
+#ifdef HAVE_FCNTL_H
+#include <fcntl.h>
+#endif
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
+#if defined(HAVE_EXECINFO_H) && defined(HAVE_BACKTRACE) && \
+  defined(HAVE_BACKTRACE_SYMBOLS_FD) && defined(HAVE_SIGACTION)
+#define USE_BACKTRACE
+#endif
+
+#if !defined(USE_BACKTRACE)
+#define NO_BACKTRACE_IMPL
+#endif
+
+static char *bt_filename = NULL;
+static char *bt_version = NULL;
+
+#ifndef NO_BACKTRACE_IMPL
+/**DOCDOC*/
+static int
+open_bt_target(void)
+{
+  int fd = -1;
+  if (bt_filename)
+    fd = open(bt_filename, O_WRONLY|O_CREAT|O_APPEND, 0700);
+  return fd;
+}
+#endif
+
+/**DOCDOC*/
+static void
+bt_write(int fd, const char *s, ssize_t n)
+{
+  int r;
+  if (n < 0) n = strlen(s);
+
+  r = write(STDERR_FILENO, s, n);
+  if (fd >= 0)
+    r = write(fd, s, n);
+  (void)r; 
+}
+
+#ifdef USE_BACKTRACE
+#define MAX_DEPTH 256
+static void *cb_buf[MAX_DEPTH];
+
+/**DOCDOC*/
+void
+dump_backtrace(const char *msg)
+{
+  char timebuf[32];
+  time_t t = time(NULL);
+  int timebuf_len;
+  int depth;
+  int fd;
+  if (!msg) msg = "unspecified crash";
+
+  depth = backtrace(cb_buf, MAX_DEPTH);
+
+  t /= 900; t *= 900; /* Round to the previous 15 minutes */
+  timebuf[0] = '\0';
+  timebuf_len = format_dec_number_sigsafe(t, timebuf, sizeof(timebuf));
+
+  fd = open_bt_target();
+  bt_write(fd, "========================================"
+               "====================================\n", -1);
+  bt_write(fd, bt_version, -1);
+  bt_write(fd, " died around T=", -1);
+  bt_write(fd, timebuf, timebuf_len);
+  bt_write(fd, ": ", 2);
+  bt_write(fd, msg, -1);
+  bt_write(fd, "\n", 1);
+  backtrace_symbols_fd(cb_buf, depth, STDERR_FILENO);
+  if (fd >= 0)
+    backtrace_symbols_fd(cb_buf, depth, fd);
+
+  close(fd);
+}
+
+/**DOCDOC*/
+static int
+install_bt_handler(void)
+{
+  /*XXXX add signal handlers */
+  /*XXXX make this idempotent */
+  return 0;
+}
+/**DOCDOC*/
+static void
+remove_bt_handler(void)
+{
+}
+#endif
+
+#ifdef NO_BACKTRACE_IMPL
+/**DOCDOC*/
+void
+dump_backtrace(const char *msg)
+{
+  bt_write(-1, bt_version, -1);
+  bt_write(-1, " died: ", -1);
+  bt_write(-1, msg, -1);
+  bt_write(-1, "\n", -1);
+}
+
+/**DOCDOC*/
+static int
+install_bt_handler(void)
+{
+  return 0;
+}
+
+/**DOCDOC*/
+static void
+remove_bt_handler(void)
+{
+}
+#endif
+
+/**DOCDOC*/
+int
+configure_backtrace_handler(const char *filename, const char *tor_version)
+{
+  tor_free(bt_filename);
+  if (filename)
+    bt_filename = tor_strdup(filename);
+  tor_free(bt_version);
+  if (!tor_version)
+    tor_version = "Tor";
+  bt_version = tor_strdup(tor_version);
+
+  return install_bt_handler();
+}
+
+/**DOCDOC*/
+void
+clean_up_backtrace_handler(void)
+{
+  remove_bt_handler();
+
+  tor_free(bt_filename);
+  tor_free(bt_version);
+}
+
diff --git a/src/common/backtrace.h b/src/common/backtrace.h
new file mode 100644
index 000000000..bb2396080
--- /dev/null
+++ b/src/common/backtrace.h
@@ -0,0 +1,12 @@
+/* Copyright (c) 2013, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#ifndef TOR_BACKTRACE_H
+#define TOR_BACKTRACE_H
+
+void dump_backtrace(const char *msg);
+int configure_backtrace_handler(const char *filename, const char *tor_version);
+void clean_up_backtrace_handler(void);
+
+#endif
+
diff --git a/src/common/include.am b/src/common/include.am
index 032befd20..814786b77 100644
--- a/src/common/include.am
+++ b/src/common/include.am
@@ -50,6 +50,7 @@ endif
 
 LIBOR_A_SOURCES = \
   src/common/address.c					\
+  src/common/backtrace.c				\
   src/common/compat.c					\
   src/common/container.c				\
   src/common/di_ops.c					\
@@ -90,6 +91,7 @@ src_common_libor_event_testing_a_CFLAGS = $(AM_CFLAGS) $(TEST_CFLAGS)
 
 COMMONHEADERS = \
   src/common/address.h				\
+  src/common/backtrace.h			\
   src/common/aes.h				\
   src/common/ciphers.inc			\
   src/common/compat.h				\
diff --git a/src/common/util.c b/src/common/util.c
index 814eb1379..0b65437b0 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -24,6 +24,7 @@
 #include "torint.h"
 #include "container.h"
 #include "address.h"
+#include "backtrace.h"
 
 #ifdef _WIN32
 #include <io.h>
@@ -101,8 +102,13 @@ void
 tor_assertion_failed_(const char *fname, unsigned int line,
                       const char *func, const char *expr)
 {
+  char buf[256];
   log_err(LD_BUG, "%s:%u: %s: Assertion %s failed; aborting.",
           fname, line, func, expr);
+  tor_snprintf(buf, sizeof(buf),
+               "Assertion %s failed in %s at %s:%u",
+               expr, func, fname, line);
+  dump_backtrace(buf);
   fprintf(stderr,"%s:%u: %s: Assertion %s failed; aborting.\n",
           fname, line, func, expr);
 }