LibJS: Don't crash when dumping a backtrace

Previously, we would crash when attempting to log a backtrace with the `--log-all-js-exceptions` option enabled. A crash would occur if the program counter value for the current frame was larger than the current executable bytecode size, or if a source mapping couldn't be found for the current program counter value.
tcl3 · Jul 24, 2024 · 0670da0 · 0670da0
1 parent 40f9c9f
commit 0670da0
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Showing 3 changed files with 13 additions and 6 deletions.
diff --git a/Userland/Libraries/LibJS/Bytecode/Executable.cpp b/Userland/Libraries/LibJS/Bytecode/Executable.cpp
@@ -98,15 +98,15 @@ Optional<Executable::ExceptionHandlers const&> Executable::exception_handlers_fo
     return {};
 }
 
-UnrealizedSourceRange Executable::source_range_at(size_t offset) const
+Optional<UnrealizedSourceRange> Executable::source_range_at(size_t offset) const
 {
     if (offset >= bytecode.size())
-        return {};
+        return OptionalNone {};
     auto it = InstructionStreamIterator(bytecode.span().slice(offset), this);
     VERIFY(!it.at_end());
     auto mapping = source_map.get(offset);
     if (!mapping.has_value())
-        return {};
+        return OptionalNone {};
     return UnrealizedSourceRange {
         .source_code = source_code,
         .start_offset = mapping->source_start_offset,

diff --git a/Userland/Libraries/LibJS/Bytecode/Executable.h b/Userland/Libraries/LibJS/Bytecode/Executable.h
@@ -100,7 +100,7 @@ class Executable final : public Cell {
 
     [[nodiscard]] Optional<ExceptionHandlers const&> exception_handlers_for_offset(size_t offset) const;
 
-    [[nodiscard]] UnrealizedSourceRange source_range_at(size_t offset) const;
+    [[nodiscard]] Optional<UnrealizedSourceRange> source_range_at(size_t offset) const;
 
     void dump() const;
 

diff --git a/Userland/Libraries/LibJS/Runtime/VM.cpp b/Userland/Libraries/LibJS/Runtime/VM.cpp
@@ -444,8 +444,15 @@ void VM::dump_backtrace() const
     for (ssize_t i = m_execution_context_stack.size() - 1; i >= 0; --i) {
         auto& frame = m_execution_context_stack[i];
         if (frame->executable && frame->program_counter.has_value()) {
-            auto source_range = frame->executable->source_range_at(frame->program_counter.value()).realize();
-            dbgln("-> {} @ {}:{},{}", frame->function_name ? frame->function_name->utf8_string() : ""_string, source_range.filename(), source_range.start.line, source_range.start.column);
+            auto unrealized_source_range = frame->executable->source_range_at(frame->program_counter.value());
+            if (unrealized_source_range.has_value()) {
+                auto source_range = unrealized_source_range->realize();
+                dbgln("-> {} @ {}:{},{}", frame->function_name ? frame->function_name->utf8_string() : ""_string, source_range.filename(), source_range.start.line, source_range.start.column);
+                continue;
+            }
+        }
+        if (frame->executable) {
+            dbgln("-> {} @ {}", frame->function_name ? frame->function_name->utf8_string() : ""_string, frame->executable->source_code->filename());
         } else {
             dbgln("-> {}", frame->function_name ? frame->function_name->utf8_string() : ""_string);
         }