From 9afa80b45d36471c02df455ba87dd4df277c768f Mon Sep 17 00:00:00 2001
From: fwsGonzo <fwsgonzo@hotmail.com>
Date: Mon, 11 Sep 2017 03:18:46 -0700
Subject: [PATCH] kernel: Add custom double fault handler to avoid triple fault

---
 src/arch/x86_64/arch_start.asm |  2 +-
 src/arch/x86_64/ist.cpp        |  4 ++--
 src/kernel/syscalls.cpp        | 39 +++++++++++++++++++++++++---------
 src/platform/x86_pc/idt.cpp    | 15 +++++++++++--
 4 files changed, 45 insertions(+), 15 deletions(-)

diff --git a/src/arch/x86_64/arch_start.asm b/src/arch/x86_64/arch_start.asm
index 055b96087e..cec61dfd91 100644
--- a/src/arch/x86_64/arch_start.asm
+++ b/src/arch/x86_64/arch_start.asm
@@ -24,7 +24,7 @@ extern __multiboot_addr
 %define P4_TAB             0x1000
 %define P3_TAB             0x2000 ;; - 0x5fff
 %define P2_TAB           0x100000
-%define STACK_LOCATION   0x9fff00
+%define STACK_LOCATION   0x9ffff0
 
 [BITS 32]
 __arch_start:
diff --git a/src/arch/x86_64/ist.cpp b/src/arch/x86_64/ist.cpp
index 4d03924bff..a5d5e7f690 100644
--- a/src/arch/x86_64/ist.cpp
+++ b/src/arch/x86_64/ist.cpp
@@ -11,7 +11,7 @@ extern gdtr64 __gdt64_base_pointer;
 
 #define INTR_SIZE  4096
 #define NMI_SIZE  20480
-#define DFI_SIZE  20480
+#define DFI_SIZE   4096
 
 namespace x86
 {
@@ -19,7 +19,7 @@ namespace x86
   {
     char* intr; // 4kb
     char* nmi;  // 20kb
-    char* dfi;  // 20kb
+    char* dfi;  // 4kb
 
     AMD64_TSS tss;
   };
diff --git a/src/kernel/syscalls.cpp b/src/kernel/syscalls.cpp
index 4fb8f57aab..a37e987f99 100644
--- a/src/kernel/syscalls.cpp
+++ b/src/kernel/syscalls.cpp
@@ -151,6 +151,9 @@ void OS::on_panic(on_panic_func func)
   panic_handler = std::move(func);
 }
 
+extern "C" __attribute__((noreturn)) void panic_epilogue(const char*);
+
+
 /**
  * panic:
  * Display reason for kernel panic
@@ -193,21 +196,37 @@ asm("panic_begin:");
   fflush(stderr);
   SMP::global_unlock();
 
-  // call custom on panic handler (if present)
-  if (panic_handler) panic_handler(why);
+  panic_epilogue(why);
+}
 
-#if defined(ARCH_x86)
+extern "C"
+void double_fault(const char* why)
+{
   SMP::global_lock();
-  // Signal End-Of-Transmission
-  kprint("\x04");
+  fprintf(stderr, "\n%s\nCPU: %d, Reason: %s\n",
+          panic_signature, SMP::cpu_id(), why);
   SMP::global_unlock();
 
-  // .. if we return from the panic handler, go to permanent sleep
-  while (1) asm("cli; hlt");
+  panic_epilogue(why);
+}
+
+void panic_epilogue(const char* why)
+{
+  // call custom on panic handler (if present)
+  if (panic_handler) panic_handler(why);
+
+  #if defined(ARCH_x86)
+    SMP::global_lock();
+    // Signal End-Of-Transmission
+    kprint("\x04");
+    SMP::global_unlock();
+
+    // .. if we return from the panic handler, go to permanent sleep
+    while (1) asm("cli; hlt");
+  #else
+    #warning "panic() handler not implemented for selected arch"
+  #endif
   __builtin_unreachable();
-#else
-  #warning "panic() handler not implemented for selected arch"
-#endif
 }
 
 // Shutdown the machine when one of the exit functions are called
diff --git a/src/platform/x86_pc/idt.cpp b/src/platform/x86_pc/idt.cpp
index 61f617d69c..c7468105b2 100644
--- a/src/platform/x86_pc/idt.cpp
+++ b/src/platform/x86_pc/idt.cpp
@@ -259,6 +259,8 @@ static void cpu_dump_regs(uintptr_t* regs)
   fprintf(stderr, "\n");
 }
 
+extern "C" void double_fault(const char*);
+
 extern "C"
 __attribute__((noreturn, optnone))
 void __cpu_exception(uintptr_t* regs, int error, uint32_t code)
@@ -270,8 +272,17 @@ void __cpu_exception(uintptr_t* regs, int error, uint32_t code)
           exception_names[error], error, (void*) regs[RIP_REG], code);
   cpu_dump_regs(regs);
   SMP::global_unlock();
-  // call panic, which will decide what to do next
+  // error message:
   char buffer[64];
   snprintf(buffer, sizeof(buffer), "%s (%d)", exception_names[error], error);
-  panic(buffer);
+  // normal CPU exception
+  if (error != 0x8) {
+    // call panic, which will decide what to do next
+    panic(buffer);
+  }
+  else {
+    // handle double faults differently
+    double_fault(buffer);
+  }
+  __builtin_unreachable();
 }