UserspaceEmulator: Use the base address of instructions in backtraces

Instead of using SoftCPU::eip() which points at the *next* instruction
most of the time, stash away a "base EIP" so we can use it when making
backtraces. This makes the correct line number show up! :^)

2 files changed, 8 insertions, 6 deletions

diff --git a/DevTools/UserspaceEmulator/Emulator.cpp b/DevTools/UserspaceEmulator/Emulator.cpp
index b07aa15e1a..1a2aaee0a7 100644
--- a/DevTools/UserspaceEmulator/Emulator.cpp
+++ b/DevTools/UserspaceEmulator/Emulator.cpp
@@ -167,14 +167,12 @@ int Emulator::exec()
     bool trace = false;
 
     while (!m_shutdown) {
-        u32 base_eip = 0;
-        if (trace)
-            base_eip = m_cpu.eip();
+        m_cpu.save_base_eip();
 
         auto insn = X86::Instruction::from_stream(m_cpu, true, true);
 
         if (trace)
-            out() << (const void*)base_eip << "  \033[33;1m" << insn.to_string(base_eip, &symbol_provider) << "\033[0m";
+            out() << (const void*)m_cpu.base_eip() << "  \033[33;1m" << insn.to_string(m_cpu.base_eip(), &symbol_provider) << "\033[0m";
 
         (m_cpu.*insn.handler())(insn);
 
@@ -190,13 +188,13 @@ int Emulator::exec()
 
 bool Emulator::is_in_malloc_or_free() const
 {
-    return (m_cpu.eip() >= m_malloc_symbol_start && m_cpu.eip() < m_malloc_symbol_end) || (m_cpu.eip() >= m_free_symbol_start && m_cpu.eip() < m_free_symbol_end);
+    return (m_cpu.base_eip() >= m_malloc_symbol_start && m_cpu.base_eip() < m_malloc_symbol_end) || (m_cpu.base_eip() >= m_free_symbol_start && m_cpu.base_eip() < m_free_symbol_end);
 }
 
 Vector<FlatPtr> Emulator::raw_backtrace()
 {
     Vector<FlatPtr> backtrace;
-    backtrace.append(m_cpu.eip());
+    backtrace.append(m_cpu.base_eip());
 
     // FIXME: Maybe do something if the backtrace has uninitialized data in the frame chain.
 
diff --git a/DevTools/UserspaceEmulator/SoftCPU.h b/DevTools/UserspaceEmulator/SoftCPU.h
index 925a8d46b2..e954873edf 100644
--- a/DevTools/UserspaceEmulator/SoftCPU.h
+++ b/DevTools/UserspaceEmulator/SoftCPU.h
@@ -56,6 +56,9 @@ public:
     explicit SoftCPU(Emulator&);
     void dump() const;
 
+    u32 base_eip() const { return m_base_eip; }
+    void save_base_eip() { m_base_eip = m_eip; }
+
     u32 eip() const { return m_eip; }
     void set_eip(u32 eip)
     {
@@ -981,6 +984,7 @@ private:
     bool m_flags_tainted { false };
 
     u32 m_eip { 0 };
+    u32 m_base_eip { 0 };
 
     const u8* m_cached_code_ptr { nullptr };
     const u8* m_cached_code_end { nullptr };