From 77400d8f5a309e4ec7d2a5dd9c2b787177075f44 Mon Sep 17 00:00:00 2001
From: Gregory Bowne <gbowne144@gmail.com>
Date: Wed, 19 Nov 2025 08:41:03 -0800
Subject: [PATCH] Update scheduler.c

old scheduler might not work on x86 IA-32 32 bit
---
 kernel/scheduler.c | 60 ++++++++++++++++++++++++++++++++++++----------
 1 file changed, 47 insertions(+), 13 deletions(-)

diff --git a/kernel/scheduler.c b/kernel/scheduler.c
index cdb8812..8514c3c 100644
--- a/kernel/scheduler.c
+++ b/kernel/scheduler.c
@@ -1,7 +1,12 @@
 #include "scheduler.h"
 #include <stddef.h>
 
+// Defined in context_switch.s
+extern void ctx_switch(uint32_t **old_sp_ptr, uint32_t *new_sp);
+
 static task_t tasks[MAX_TASKS];
+
+// Stack memory area. Note: x86 Stacks grow DOWN from high to low addresses.
 static uint32_t task_stacks[MAX_TASKS][STACK_SIZE / sizeof(uint32_t)];
 
 static int task_count = 0;
@@ -9,7 +14,6 @@ static task_t *task_list = NULL;
 static task_t *current_task = NULL;
 
 void scheduler_init() {
-    // Initialize task list, etc.
     task_list = NULL;
     current_task = NULL;
     task_count = 0;
@@ -20,16 +24,42 @@ void scheduler_add_task(void (*entry)(void)) {
 
     task_t *new_task = &tasks[task_count];
     new_task->id = task_count;
-    new_task->entry = entry;
 
-    // Simulate a stack pointer pointing to the "top" of the stack
-    new_task->stack_ptr = &task_stacks[task_count][STACK_SIZE / sizeof(uint32_t) - 1];
+    // 1. Calculate the top of the stack (High Address)
+    // We point to the very end of the array.
+    uint32_t *sp = &task_stacks[task_count][STACK_SIZE / sizeof(uint32_t)];
 
+    // 2. "Forge" the stack frame to look like ctx_switch saved it.
+    // We push values onto the stack by decrementing the pointer and writing.
+
+    // --- Return Address (EIP) ---
+    sp--; 
+    *sp = (uint32_t)entry; // When ctx_switch does 'ret', it pops this and jumps to 'entry'
+
+    // --- EFLAGS ---
+    sp--;
+    *sp = 0x00000202; // Reserved bit set, Interrupts Enabled (IF=1). Important!
+
+    // --- General Purpose Registers (PUSHA/POPA layout) ---
+    // Order: EAX, ECX, EDX, EBX, ESP, EBP, ESI, EDI
+    // We initialize them to 0 or meaningful values.
+    sp--; *sp = 0; // EAX
+    sp--; *sp = 0; // ECX
+    sp--; *sp = 0; // EDX
+    sp--; *sp = 0; // EBX
+    sp--; *sp = 0; // ESP (Ignored by POPA)
+    sp--; *sp = 0; // EBP
+    sp--; *sp = 0; // ESI
+    sp--; *sp = 0; // EDI
+
+    // Save this final stack location to the TCB
+    new_task->stack_ptr = sp;
     new_task->next = NULL;
 
-    // Add to task list
+    // 3. Add to linked list
     if (task_list == NULL) {
         task_list = new_task;
+        current_task = new_task; // Make sure we have a current task to start
     } else {
         task_t *tail = task_list;
         while (tail->next) {
@@ -42,21 +72,25 @@ void scheduler_add_task(void (*entry)(void)) {
 }
 
 void scheduler_schedule() {
-    // Very basic round-robin switch
-    if (current_task && current_task->next) {
+    if (!current_task) return;
+
+    task_t *prev = current_task;
+    
+    // Round-robin logic
+    if (current_task->next) {
         current_task = current_task->next;
     } else {
-        current_task = task_list; // Loop back
+        current_task = task_list;
     }
 
-    // Call context switch or simulate yielding to current_task
-    // In real system: context_switch_to(current_task)
-    if (current_task && current_task->entry) {
-        current_task->entry();  // Simulate switching by calling
+    // Perform the ACTUAL context switch
+    // We pass the address of the previous task's stack pointer storage
+    // and the value of the new task's stack pointer.
+    if (prev != current_task) {
+        ctx_switch(&prev->stack_ptr, current_task->stack_ptr);
     }
 }
 
 void scheduler_yield() {
-    // Stub: manually call schedule for cooperative multitasking
     scheduler_schedule();
 }