From 2114741766f1c13f40d86d1c845627e033a837d0 Mon Sep 17 00:00:00 2001
From: Lucia Ceionia <lucia@noreply.ceionius.com>
Date: Thu, 2 Feb 2023 18:15:14 -0600
Subject: [PATCH] Might? have fixed one race condition bug. Still crashing for
 unknown reasons on my laptop rarely

---
 fault.nasm    | 21 +++++++++++++++++++--
 kernel.c      | 26 ++++++++++++++++++--------
 usermode.nasm |  3 +++
 3 files changed, 40 insertions(+), 10 deletions(-)

diff --git a/fault.nasm b/fault.nasm
index 4f580ce..ee8fd84 100644
--- a/fault.nasm
+++ b/fault.nasm
@@ -6,8 +6,8 @@ _fault_coda:
 xchg bx,bx
 mov ax, 0x10
 mov es, ax
-; move to TOP OF kernel stack
-mov ebp, 0x400000
+; move to 'safe' location
+mov ebp, 0x318000
 mov esp, ebp
 call error_environment
 .hlt:
@@ -17,13 +17,30 @@ jmp .hlt
 extern gpf_handler_v86
 global gpfHandler
 gpfHandler:
+cli ; make sure we're in a 'friendly' env
 push eax
 push ebx
+push ecx
+; save old ds
 mov bx, ds
 mov ax, 0x10
 mov ds, ax
 mov word [_gpf_old_ds], bx
+; relocate stack so other interrupts don't fuck us over
+; not sure if this is necessary, it doesn't seem to fix our race conditions...
+mov ebx, esp
+sub esp, 0x1000
+xor ecx, ecx
+.l:
+mov eax, [ebx]
+mov [esp+ecx], eax
+add ebx, 4
+add ecx, 4
+cmp ebx, 0x320000 ; tss esp0
+jl .l
+pop ecx
 pop ebx
+sti ; we shouldn't crash now?
 mov eax, dword [esp+16] ; EFLAGS
 and eax, 1 << 17 ; VM flag
 test eax, eax
diff --git a/kernel.c b/kernel.c
index b884222..5e3f6d1 100644
--- a/kernel.c
+++ b/kernel.c
@@ -112,7 +112,7 @@ void error_environment() {
     for (int i = 0; i < 80*50; i++)
         vga_text[i] = error_screen[i];
     uint8_t key;
-    for (key = get_key(); key != 'e' && key != 'E'; key = get_key());
+    while (key = get_key(), key != 'e' && key != 'E');
     v86_entry = i386LinearToFp(v86TransFlag);
     enter_v86(0x8000, 0xFF00, FP_SEG(v86_entry), FP_OFF(v86_entry), &regs);
 }
@@ -311,12 +311,22 @@ void start() {
     kbd_wait();
 
     vga_text = &((uint16_t*)0xB8000)[80*16];
-    vga_text += printStr("Press ` for a flagrant system error... ", vga_text);
-    while ((key = get_key()) != '`') {
-        *vga_text = (*vga_text & 0xFF00) | key;
-        vga_text++;
-    }
-    // flagrant system error
-    *((uint8_t*)0x1000000) = 0;
+    vga_text += printStr("Press E for a flagrant system error. Press C to continue... ", vga_text);
+    for (char l = 1;l;) { switch (key = get_key()) {
+        case 'e':
+        case 'E':
+            // flagrant system error
+            *((uint8_t*)0x1000000) = 0;
+            break;
+        case 'c':
+        case 'C':
+            // continue
+            l = 0;
+            break;
+        default:
+            *vga_text = (*vga_text & 0xFF00) | key;
+            vga_text++;
+            break;
+    }}
 }
 
diff --git a/usermode.nasm b/usermode.nasm
index 00a6b64..72316c3 100644
--- a/usermode.nasm
+++ b/usermode.nasm
@@ -26,6 +26,9 @@ inc al
 cmp eax, 200
 jl .loop
 mov eax, 0xA0000
+;mov ecx, 1000000000
+;.dbg:
+;loop .dbg
 int 0x30 ; Exit
 mov edx, 0x105000 ; somewhere in kernel mem
 mov edx, [edx] ; should page fault