From af635957efca0dfcd79e7c297a69db36e4971e98 Mon Sep 17 00:00:00 2001
From: Karen Arutyunov <karen@codesynthesis.com>
Date: Tue, 28 May 2019 12:09:42 +0300
Subject: Print backtrace to stderr when terminating due to unhandled exception

---
 build2/b.cxx         | 24 +++++++++++++++++++++---
 build2/buildfile     |  7 +++++++
 build2/scheduler.cxx |  6 ++++++
 build2/scheduler.hxx |  2 +-
 4 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/build2/b.cxx b/build2/b.cxx
index 882b469..022df9d 100644
--- a/build2/b.cxx
+++ b/build2/b.cxx
@@ -13,12 +13,14 @@
 #endif
 
 #include <sstream>
-#include <cstring>     // strcmp(), strchr()
+#include <cstring>   // strcmp(), strchr()
 #include <typeinfo>
-#include <iostream>    // cout
+#include <iostream>  // cout
+#include <exception> // set_terminate(), terminate_handler
 
 #include <libbutl/pager.mxx>
-#include <libbutl/fdstream.mxx> // stderr_fd(), fdterm()
+#include <libbutl/fdstream.mxx>  // stderr_fd(), fdterm()
+#include <libbutl/backtrace.mxx> // backtrace()
 
 #include <build2/types.hxx>
 #include <build2/utility.hxx>
@@ -131,9 +133,25 @@ namespace build2
   }
 }
 
+// Print backtrace if terminating due to an unhandled exception. Note that
+// custom_terminate is non-static and not a lambda to reduce the noise.
+//
+static terminate_handler default_terminate;
+
+void
+custom_terminate ()
+{
+  *diag_stream << backtrace ();
+
+  if (default_terminate != nullptr)
+    default_terminate ();
+}
+
 int build2::
 main (int argc, char* argv[])
 {
+  default_terminate = set_terminate (custom_terminate);
+
   tracer trace ("main");
 
   int r (0);
diff --git a/build2/buildfile b/build2/buildfile
index bf3f10b..ba8f25c 100644
--- a/build2/buildfile
+++ b/build2/buildfile
@@ -51,7 +51,14 @@ if ($cxx.target == $build.host)
 }
 
 if ($cxx.target.class != "windows")
+{
+  # Make sure backtrace includes function names.
+  #
+  if ($cxx.target.class == 'linux')
+    cxx.loptions += -rdynamic
+
   cxx.libs += -lpthread
+}
 else
 {
   # Adjust stack size (affects all threads).
diff --git a/build2/scheduler.cxx b/build2/scheduler.cxx
index 790f2f6..ad3a640 100644
--- a/build2/scheduler.cxx
+++ b/build2/scheduler.cxx
@@ -588,6 +588,12 @@ namespace build2
     // inherit the main thread's stack size (since the first helper is always
     // created by the main thread).
     //
+    // Note also the interaction with our backtrace functionality: in order to
+    // get the complete stack trace we let unhandled exceptions escape the
+    // thread function expecting the runtime to still call std::terminate. In
+    // particular, having a noexcept function anywhere on the exception's path
+    // causes the stack trace to be truncated, at least on Linux.
+    //
 #if defined(__linux__) || defined(__FreeBSD__) || defined(__APPLE__)
 
 #ifndef BUILD2_DEFAULT_STACK_SIZE
diff --git a/build2/scheduler.hxx b/build2/scheduler.hxx
index cd3693b..3aa1dc5 100644
--- a/build2/scheduler.hxx
+++ b/build2/scheduler.hxx
@@ -370,7 +370,7 @@ namespace build2
 
       template <size_t... i>
       void
-      thunk (std::index_sequence<i...>) noexcept
+      thunk (std::index_sequence<i...>)
       {
         move (func) (std::get<i> (move (args))...);
       }
-- 
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