[tor-commits] [tor/master] Make backtrace handler handle signals correctly.
nickm at torproject.org
nickm at torproject.org
Mon Nov 18 16:04:37 UTC 2013
commit d631ddfb59eca910d1faf45a711da630bab7c89a
Author: Nick Mathewson <nickm at torproject.org>
Date: Fri Jul 26 13:22:56 2013 +0200
Make backtrace handler handle signals correctly.
This meant moving a fair bit of code around, and writing a signal
cleanup function. Still pretty nice from what I can tell, though.
---
src/common/backtrace.c | 125 +++++++++++++++++++++++++++++++++++++++++-------
src/common/backtrace.h | 2 +-
src/common/util.c | 4 +-
3 files changed, 111 insertions(+), 20 deletions(-)
diff --git a/src/common/backtrace.c b/src/common/backtrace.c
index 2c49146..9c69e4f 100644
--- a/src/common/backtrace.c
+++ b/src/common/backtrace.c
@@ -7,6 +7,8 @@
#include "util.h"
#include "torlog.h"
+#define __USE_GNU
+
#ifdef HAVE_EXECINFO_H
#include <execinfo.h>
#endif
@@ -16,6 +18,15 @@
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
+#ifdef HAVE_SIGNAL_H
+#include <signal.h>
+#endif
+#ifdef HAVE_UCONTEXT_H
+#include <ucontext.h>
+#endif
+#ifdef HAVE_SYS_UCONTEXT_H
+#include <sys/ucontext.h>
+#endif
#if defined(HAVE_EXECINFO_H) && defined(HAVE_BACKTRACE) && \
defined(HAVE_BACKTRACE_SYMBOLS_FD) && defined(HAVE_SIGACTION)
@@ -26,53 +37,135 @@
#define NO_BACKTRACE_IMPL
#endif
+/** Version of Tor to report in backtrace messages. */
static char *bt_version = NULL;
#ifdef USE_BACKTRACE
+/** Largest stack depth to try to dump. */
#define MAX_DEPTH 256
+/** Static allocation of stack to dump. This is static so we avoid stack
+ * pressure. */
static void *cb_buf[MAX_DEPTH];
-/**DOCDOC*/
+/** Change a stacktrace in <b>stack</b> of depth <b>depth</b> so that it will
+ * log the correct function from which a signal was received with context
+ * <b>ctx</b>. (When we get a signal, the current function will not have
+ * called any other function, and will therefore have not pushed its address
+ * onto the stack. Fortunately, we usually have the program counter in the
+ * ucontext_t structure.
+ */
+static void
+clean_backtrace(void **stack, int depth, const ucontext_t *ctx)
+{
+#ifdef PC_FROM_UCONTEXT
+#if defined(__linux__)
+ const int n = 1;
+#elif defined(__darwin__) || defined(__APPLE__) || defined(__OpenBSD__) \
+ || defined(__FreeBSD__)
+ const int n = 2;
+#else
+ const int n = 1;
+#endif
+ if (depth <= n)
+ return;
+
+ stack[n] = (void*) ctx->PC_FROM_UCONTEXT;
+#else
+ (void) depth;
+ (void) ctx;
+#endif
+}
+
+/** Log a message <b>msg</b> at <b>severity</b> in <b>domain</b>, and follow
+ * that with a backtrace log. */
void
-dump_backtrace(const char *msg)
+log_backtrace(int severity, int domain, const char *msg)
{
- int depth;
- const int *fds;
- int n_fds;
+ int depth = backtrace(cb_buf, MAX_DEPTH);
+ char **symbols = backtrace_symbols(cb_buf, depth);
int i;
+ tor_log(severity, domain, "%s. Stack trace:", msg);
+ if (!symbols) {
+ tor_log(severity, domain, " Unable to generate backtrace.");
+ return;
+ }
+ for (i=0; i < depth; ++i) {
+ tor_log(severity, domain, " %s", symbols[i]);
+ }
+ free(symbols);
+}
- if (!msg) msg = "unspecified crash";
+static void crash_handler(int sig, siginfo_t *si, void *ctx_)
+ __attribute__((noreturn));
+
+/** Signal handler: write a crash message with a stack trace, and die. */
+static void
+crash_handler(int sig, siginfo_t *si, void *ctx_)
+{
+ char buf[40];
+ int depth;
+ ucontext_t *ctx = (ucontext_t *) ctx_;
+ int n_fds, i;
+ const int *fds = NULL;
+
+ (void) si;
depth = backtrace(cb_buf, MAX_DEPTH);
+ /* Clean up the top stack frame so we get the real function
+ * name for the most recently failing function. */
+ clean_backtrace(cb_buf, depth, ctx);
+
+ format_dec_number_sigsafe((unsigned)sig, buf, sizeof(buf));
- tor_log_err_sigsafe(bt_version, " died: ", msg, "\n",
+ tor_log_err_sigsafe(bt_version, " died: Caught signal ", buf, "\n",
NULL);
+
n_fds = tor_log_get_sigsafe_err_fds(&fds);
for (i=0; i < n_fds; ++i)
backtrace_symbols_fd(cb_buf, depth, fds[i]);
+
+ abort();
}
-/**DOCDOC*/
+/** Install signal handlers as needed so that when we crash, we produce a
+ * useful stack trace. Return 0 on success, -1 on failure. */
static int
install_bt_handler(void)
{
- /*XXXX add signal handlers */
/*XXXX make this idempotent */
- return 0;
+ int trap_signals[] = { SIGSEGV, SIGILL, SIGFPE, SIGBUS, SIGSYS,
+ SIGIO, -1 };
+ int i, rv=0;
+
+ struct sigaction sa;
+ memset(&sa, 0, sizeof(sa));
+ sa.sa_sigaction = crash_handler;
+ sa.sa_flags = SA_SIGINFO;
+ sigfillset(&sa.sa_mask);
+
+ for (i = 0; trap_signals[i] >= 0; ++i) {
+ if (sigaction(trap_signals[i], &sa, NULL) == -1) {
+ log_warn(LD_BUG, "Sigaction failed: %s", strerror(errno));
+ rv = -1;
+ }
+ }
+ return rv;
}
-/**DOCDOC*/
+
+/** Uninstall crash handlers. */
static void
remove_bt_handler(void)
{
+ /*XXXX writeme*/
}
#endif
#ifdef NO_BACKTRACE_IMPL
-/**DOCDOC*/
+/**DOCDOC */
void
-dump_backtrace(const char *msg)
+log_backtrace(int severity, int domain, const char *msg)
{
- tor_log_err_sigsafe(bt_version, " died: ", msg, "\n", NULL);
+ tor_log(severity, domain, "%s. (Stack trace not available)", msg);
}
/**DOCDOC*/
@@ -95,8 +188,8 @@ configure_backtrace_handler(const char *tor_version)
{
tor_free(bt_version);
if (!tor_version)
- tor_version = "Tor";
- bt_version = tor_strdup(tor_version);
+ tor_version = "";
+ tor_asprintf(&bt_version, "Tor %s", tor_version);
return install_bt_handler();
}
diff --git a/src/common/backtrace.h b/src/common/backtrace.h
index 7d7c10a..765436f 100644
--- a/src/common/backtrace.h
+++ b/src/common/backtrace.h
@@ -4,7 +4,7 @@
#ifndef TOR_BACKTRACE_H
#define TOR_BACKTRACE_H
-void dump_backtrace(const char *msg);
+void log_backtrace(int severity, int domain, const char *msg);
int configure_backtrace_handler(const char *tor_version);
void clean_up_backtrace_handler(void);
diff --git a/src/common/util.c b/src/common/util.c
index 0b65437..bbb6044 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -108,9 +108,7 @@ tor_assertion_failed_(const char *fname, unsigned int line,
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);
+ log_backtrace(LOG_ERR, LD_BUG, buf);
}
/* =====
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