From 6f6a2dc3198fcdd0deef5871ed9ede86f9c4eb9c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=B6nke=20Holz?= <sholz8530@gmail.com>
Date: Thu, 4 Jan 2024 02:03:08 +0100
Subject: [PATCH] HackStudio: Correctly handle invalid addresses during
 backtrace creation

This fixes a bug where we previously would hang if we couldn't find a
library containing the current program counter.
---
 .../HackStudio/Debugger/BacktraceModel.cpp    | 30 +++++++++++--------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/Userland/DevTools/HackStudio/Debugger/BacktraceModel.cpp b/Userland/DevTools/HackStudio/Debugger/BacktraceModel.cpp
index e03fa63624..71f17bbb06 100644
--- a/Userland/DevTools/HackStudio/Debugger/BacktraceModel.cpp
+++ b/Userland/DevTools/HackStudio/Debugger/BacktraceModel.cpp
@@ -39,22 +39,26 @@ Vector<BacktraceModel::FrameInfo> BacktraceModel::create_backtrace(Debug::Proces
     size_t frame_index = 0;
     do {
         auto lib = inspector.library_at(current_program_counter);
-        if (!lib)
-            continue;
 
-        // After the first frame, current_instruction holds the return address from the function call.
-        // We need to go back to the 'call' instruction to get accurate source position information.
-        if (frame_index > 0)
-            --current_program_counter;
-        ByteString name = lib->debug_info->elf().symbolicate(current_program_counter - lib->base_address);
-        if (name.is_empty()) {
-            dbgln("BacktraceModel: couldn't find containing function for address: {:p} (library={})", current_program_counter, lib->name);
-            name = "<missing>";
+        if (lib) {
+            // After the first frame, current_instruction holds the return address from the function call.
+            // We need to go back to the 'call' instruction to get accurate source position information.
+            if (frame_index > 0)
+                --current_program_counter;
+            ByteString name = lib->debug_info->elf().symbolicate(current_program_counter - lib->base_address);
+            if (name.is_empty()) {
+                dbgln("BacktraceModel: couldn't find containing function for address: {:p} (library={})", current_program_counter, lib->name);
+                name = "<missing>";
+            }
+
+            auto source_position = lib->debug_info->get_source_position(current_program_counter - lib->base_address);
+
+            frames.append({ name, current_program_counter, current_frame_pointer, source_position });
+        } else {
+            dbgln("BacktraceModel: couldn't find containing library for address: {:p}", current_program_counter);
+            frames.append({ "<missing>", current_program_counter, current_frame_pointer, {} });
         }
 
-        auto source_position = lib->debug_info->get_source_position(current_program_counter - lib->base_address);
-
-        frames.append({ name, current_program_counter, current_frame_pointer, source_position });
         auto frame_info = Debug::StackFrameUtils::get_info(inspector, current_frame_pointer);
         VERIFY(frame_info.has_value());
         current_program_counter = frame_info.value().return_address;