Add a hack to the fatal signal handlers to invoke gdb and get a full stack

trace on crash.  This won't fix anything, but by activating this mode

in the testsuite, we can get more detail on the alpha and sparc FTBFSes.

Index: monotone-1.0/src/unix/main.cc

===================================================================

--- monotone-1.0.orig/src/unix/main.cc	2009-04-12 13:39:49.000000000 -0700

+++ monotone-1.0/src/unix/main.cc	2009-04-12 13:42:56.000000000 -0700

@@ -36,12 +36,21 @@

 #include "../base.hh"

 #include <signal.h>

-#include <time.h>

+#include <stdlib.h>

 #include <string.h>

 #include <sys/resource.h>

 #include <unistd.h>

+#include <time.h>

+

+#if __GLIBC__ >= 3 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 1)

+# define HAVE_BACKTRACE

+# include <execinfo.h>

+#endif

 static char const * argv0;

+#ifdef HAVE_BACKTRACE

+static bool backtrace_on_crash = false;

+#endif

 // a convenient wrapper

 inline void

@@ -75,6 +84,18 @@

   write_str_to_stderr("do not send a core dump, but if you have one, "

                       "\nplease preserve it in case we ask you for "

                       "information from it.\n");

+#ifdef HAVE_BACKTRACE

+  if (backtrace_on_crash)

+    {

+      void *tracebuf[20];

+      int frames = backtrace(tracebuf, 20);

+      if (frames)

+        {

+          write_str_to_stderr("stack trace:\n");

+          backtrace_symbols_fd(tracebuf, frames, 2);

+        }

+    }

+#endif

   raise(signo);

   // The signal has been reset to the default handler by SA_RESETHAND

@@ -129,6 +150,12 @@

   argv0 = argv[0];

+#ifdef HAVE_BACKTRACE

+  char *ev = getenv("MTN_STACKTRACE_ON_CRASH");

+  if (ev && ev[0])

+    backtrace_on_crash = true;

+#endif

+

   bug_signal_action.sa_flags   = SA_RESETHAND;

   bug_signal_action.sa_handler = &bug_signal;

   sigemptyset(&bug_signal_action.sa_mask);