From 9e00d833996fe78d6f0d46d74358950fcec496c7 Mon Sep 17 00:00:00 2001
From: foxostro <foxostro@gmail.com>
Date: Tue, 19 Mar 2019 22:17:18 -0700
Subject: [PATCH] PanicKernel prints a backtrace using _Unwind_Backtrace().

---
 Kernel/src/platform/i386/panic.cpp | 31 ++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/Kernel/src/platform/i386/panic.cpp b/Kernel/src/platform/i386/panic.cpp
index 8e621fd..fff7454 100644
--- a/Kernel/src/platform/i386/panic.cpp
+++ b/Kernel/src/platform/i386/panic.cpp
@@ -4,11 +4,13 @@
 #include <common/text_terminal.hpp>
 #include <halt.h>
 #include <interrupt_asm.h>
-#include <backtrace.hpp> // for enumerate_stack_frames()
+#include <unwind.h> // for _Unwind_* symbols
 
 #include <cstdio>
 #include <cstdarg>
 
+static _Unwind_Reason_Code trace(struct _Unwind_Context* context, void* param);
+
 class PanicKernel : private KernelPolicy {
 public:
     virtual ~PanicKernel() = default;
@@ -17,7 +19,7 @@ class PanicKernel : private KernelPolicy {
      : message_(message),
        terminal_(display_)
     {
-        hardware_interrupt_controller_.init(/*panic=*/ true);
+        // hardware_interrupt_controller_.init(/*panic=*/ true);
     }
 
     __attribute__((noreturn)) void run() noexcept
@@ -39,14 +41,22 @@ class PanicKernel : private KernelPolicy {
     void backtrace()
     {
         puts("Back Trace:\n");
-        enumerate_stack_frames([&](uintptr_t instruction_pointer){
+        _Unwind_Backtrace(::trace, reinterpret_cast<void*>(this));
+        puts("End Back Trace\n");
+    }
+
+    _Unwind_Reason_Code trace(struct _Unwind_Context* context)
+    {
+        void* ip = reinterpret_cast<void*>(_Unwind_GetIP(context));
+        if (ip) {
             char buffer[32] = {0};
-            snprintf(buffer, sizeof(buffer),
-                     "[%p]\n",
-                     reinterpret_cast<void*>(instruction_pointer));
+            snprintf(buffer, sizeof(buffer), "[%p]\n",
+                    reinterpret_cast<void*>(ip));
             puts(buffer);
-        });
-        puts("End Back Trace\n");
+            return _URC_NO_REASON;
+        } else {
+            return _URC_END_OF_STACK;
+        }
     }
 
     __attribute__((noreturn)) void interrupt() noexcept
@@ -65,6 +75,11 @@ class PanicKernel : private KernelPolicy {
     LoggerTextOutputStream logger_;
 };
 
+static _Unwind_Reason_Code trace(struct _Unwind_Context* context, void* param)
+{
+    return reinterpret_cast<PanicKernel*>(param)->trace(context);
+}
+
 static PanicKernel* g_panic_kernel;
 
 // Prints a message to the screen and halts forever.