From 736a4c2fb742b92527ccb0e502829567fc55fad1 Mon Sep 17 00:00:00 2001
From: Robin Sommer <robin@corelight.com>
Date: Thu, 19 Oct 2023 17:23:21 +0200
Subject: [PATCH] Disable capturing backtraces with HILTI exceptions in
 non-debug builds.

They can be expensive to capture, and aren't used anywhere by default
unless explicitly requested.

Closes #1565.
---
 hilti/runtime/include/exception.h      | 7 ++++++-
 hilti/runtime/src/configuration.cc     | 5 +++++
 hilti/runtime/src/exception.cc         | 2 ++
 hilti/toolchain/src/compiler/driver.cc | 2 ++
 4 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/hilti/runtime/include/exception.h b/hilti/runtime/include/exception.h
index 433e82a3b..08b06a256 100644
--- a/hilti/runtime/include/exception.h
+++ b/hilti/runtime/include/exception.h
@@ -49,11 +49,13 @@ class Exception : public std::runtime_error {
     /** Returns the location associated with the exception. */
     auto location() const { return _location; }
 
+#ifndef NDEBUG
     /**
      * Returns a stack backtrace captured at the time the exception was
      * thrown.
      */
     auto backtrace() const { return _backtrace.backtrace(); }
+#endif
 
 protected:
     enum Internal {};
@@ -66,7 +68,10 @@ class Exception : public std::runtime_error {
 
     std::string _description;
     std::string _location;
-    Backtrace _backtrace;
+
+#ifndef NDEBUG
+    Backtrace _backtrace; // capturing the backtrace can be pretty expensive, so limit to debug builds
+#endif
 };
 
 inline std::ostream& operator<<(std::ostream& stream, const Exception& e) { return stream << e.what(); }
diff --git a/hilti/runtime/src/configuration.cc b/hilti/runtime/src/configuration.cc
index 9633cb4eb..2abc400c6 100644
--- a/hilti/runtime/src/configuration.cc
+++ b/hilti/runtime/src/configuration.cc
@@ -24,5 +24,10 @@ void configuration::set(Configuration cfg) {
     if ( isInitialized() )
         hilti::rt::fatalError("attempt to change configuration after library has already been initialized");
 
+#ifndef NDEBUG
+    if ( cfg.show_backtraces )
+        hilti::rt::warning("printing of exception backtraces enabled, but not supported in release builds");
+#endif
+
     *detail::__configuration = std::move(cfg);
 }
diff --git a/hilti/runtime/src/exception.cc b/hilti/runtime/src/exception.cc
index 1a30eee0f..e1efa9c51 100644
--- a/hilti/runtime/src/exception.cc
+++ b/hilti/runtime/src/exception.cc
@@ -41,6 +41,7 @@ HILTI_EXCEPTION_IMPL(StackSizeExceeded)
 static void printException(const std::string& msg, const Exception& e, std::ostream& out) {
     out << "[libhilti] " << msg << " " << demangle(typeid(e).name()) << ": " << e.what() << std::endl;
 
+#ifndef NDEBUG
     if ( ! configuration::get().show_backtraces )
         return;
 
@@ -52,6 +53,7 @@ static void printException(const std::string& msg, const Exception& e, std::ostr
 
     for ( const auto& s : *bt )
         out << "[libhilti]    " << s << "\n";
+#endif
 }
 
 Exception::Exception(Internal, const char* type, const std::string& what, std::string_view desc,
diff --git a/hilti/toolchain/src/compiler/driver.cc b/hilti/toolchain/src/compiler/driver.cc
index 2c95a5792..44448610d 100644
--- a/hilti/toolchain/src/compiler/driver.cc
+++ b/hilti/toolchain/src/compiler/driver.cc
@@ -1167,6 +1167,7 @@ Result<Nothing> Driver::jitUnits() {
 void Driver::printHiltiException(const hilti::rt::Exception& e) {
     std::cerr << fmt("uncaught exception %s: %s", util::demangle(typeid(e).name()), e.what()) << std::endl;
 
+#ifndef NDEBUG
     if ( _driver_options.show_backtraces ) {
         if ( auto bt = e.backtrace(); ! bt->empty() ) {
             std::cerr << "backtrace:\n";
@@ -1175,6 +1176,7 @@ void Driver::printHiltiException(const hilti::rt::Exception& e) {
                 std::cerr << "  " << s << "\n";
         }
     }
+#endif
 }
 
 Result<Nothing> Driver::initRuntime() {