#
# This patch adds an automatic backtrace to internal errors in
# libtorrent/rtorrent, on systems that support backtrace().
#
# After applying the patch, you must run autogen.sh for both
# libtorrent and rtorrent.
#
# To make it useful, you must configure libtorrent and rtorrent
# with "-rdynamic" in the LDFLAGS. Unless you have other LDFLAGS
# you need to use, configure both like this:
#	./configure LDFLAGS=-rdynamic
# Of course add any other options you need in addition.
#
# After configuring each, check for the following line:
#	"checking for execinfo.h... yes".
# Also, config.h should have "#define USE_EXECINFO 1"
#
# If it does not, your system probably doesn't support backtrace()
# and so this patch will be useless.
#
# =================================================================
Index: rtorrent/src/main.cc
===================================================================
--- rtorrent/src/main.cc	(revision 1105)
+++ rtorrent/src/main.cc	(working copy)
@@ -324,6 +324,19 @@
     control->core()->download_list()->session_save();
     control->cleanup();
 
+#ifdef USE_EXECINFO
+  } catch (torrent::internal_error& e) {
+    control->cleanup_exception();
+
+    std::cout << "rtorrent: " << e.what() << std::endl;
+    char** stackStrings = backtrace_symbols(e.get_stack(), e.stack_size());
+
+    for (int i = 0; i < e.stack_size(); ++i)
+      std::cout << i << ' ' << stackStrings[i] << std::endl;
+
+    return -1;
+#endif
+
   } catch (std::exception& e) {
     control->cleanup_exception();
 
Index: libtorrent/scripts/common.m4
===================================================================
--- libtorrent/scripts/common.m4	(revision 1105)
+++ libtorrent/scripts/common.m4	(working copy)
@@ -184,7 +184,7 @@
 AC_DEFUN([TORRENT_CHECK_EXECINFO], [
   AC_MSG_CHECKING(for execinfo.h)
 
-  AC_RUN_IFELSE(
+  AC_LINK_IFELSE(
     [[#include <execinfo.h>
       int main() { backtrace((void**)0, 0); backtrace_symbols((char**)0, 0); return 0;}
     ]],
Index: libtorrent/src/torrent/exceptions.cc
===================================================================
--- libtorrent/src/torrent/exceptions.cc	(revision 1105)
+++ libtorrent/src/torrent/exceptions.cc	(working copy)
@@ -39,6 +39,10 @@
 #include <cerrno>
 #include <cstring>
 
+#ifdef USE_EXECINFO
+#include <execinfo.h>
+#endif
+
 #include "exceptions.h"
 
 namespace torrent {
@@ -47,9 +51,22 @@
 // exceptions. This allows us to create breakpoints at throws. This is
 // limited to rarely thrown exceptions.
 
-internal_error::internal_error(const char* msg) : m_msg(msg) {
+internal_error::internal_error(const char* msg) :
+  m_msg(msg),
+  m_stackSize(0) {
+
+#ifdef USE_EXECINFO
+  m_stackSize = backtrace(m_stackPtrs, 20);
+#endif
 }
-internal_error::internal_error(const std::string& msg) : m_msg(msg) {
+
+internal_error::internal_error(const std::string& msg) :
+  m_msg(msg),
+  m_stackSize(0) {
+
+#ifdef USE_EXECINFO
+  m_stackSize = backtrace(m_stackPtrs, 20);
+#endif
 }
 
 communication_error::communication_error(const char* msg) : m_msg(msg) {}
Index: libtorrent/src/torrent/exceptions.h
===================================================================
--- libtorrent/src/torrent/exceptions.h	(revision 1105)
+++ libtorrent/src/torrent/exceptions.h	(working copy)
@@ -66,8 +66,15 @@
 
   virtual const char* what() const throw() { return m_msg.c_str(); }
 
+  typedef void* stack_t[20];
+
+  int                 stack_size()         { return m_stackSize; }
+  stack_t&            get_stack()          { return m_stackPtrs; }
+
 private:
   std::string m_msg;
+  int         m_stackSize;
+  stack_t     m_stackPtrs;
 };
 
 // For some reason we couldn't talk with a protocol/tracker, migth be a
Index: libtorrent/configure.ac
===================================================================
--- libtorrent/configure.ac	(revision 1105)
+++ libtorrent/configure.ac	(working copy)
@@ -81,6 +81,7 @@
 	          CXXFLAGS="$CXXFLAGS $STUFF_CFLAGS";
 		  LIBS="$LIBS $STUFF_LIBS")
 
+TORRENT_CHECK_EXECINFO()
 TORRENT_CHECK_MADVISE()
 TORRENT_MINCORE()
 TORRENT_OTFD()