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Update scheduler.c

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old scheduler might not work on x86 IA-32 32 bit
This commit is contained in:
Gregory Kenneth Bowne
2025-11-19 08:41:03 -08:00
committed by GitHub
parent cdf5676085
commit 77400d8f5a
1 changed files with 47 additions and 13 deletions
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60
kernel/scheduler.c
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@@ -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();
}