sched: Implement basic scheduling and signal handling system

Note: this is probably 25% broken, but it works right now as written, so I hope it all works.

- Added a new scheduler header file (scheduler.h) defining task structures, scheduling policies, and signal handling mechanisms.
- Integrated scheduling functions into the syscall interface, including SYS_GETPID, SYS_GETPPID, SYS_EXIT, SYS_SCHED_YIELD, SYS_NICE, SYS_KILL, SYS_SIGACTION, SYS_SIGPROCMASK, SYS_SCHED_GETSCHEDULER, and SYS_SCHED_SETSCHEDULER.
- Updated syscall handler to manage new scheduling-related syscalls and signal actions.

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

src/arch/x86_64/cpu/usermode.c

@@ -5,24 +5,53 @@
 #include "mm/memory.h"
 #include "libk/stdio.h"
 #include "fs/elf.h"
+#include "sched/scheduler.h"
 
 extern uintptr_t g_hhdm_offset;
 
 #define USER_STACK_TOP 0x00007FFFFFFFE000ULL
-#define USER_STACK_PAGES 4
+#define USER_STACK_PAGES 8
 #define USER_STACK_SIZE   (USER_STACK_PAGES * PAGE_SIZE)
 
-#define PTE_PRESENT  (1ULL << 0)
-#define PTE_WRITABLE (1ULL << 1)
-#define PTE_USER     (1ULL << 2)
+
 
 
 
 static uint64_t user_stack_phys_base = 0;
 
-extern struct pagemap *kernel_pagemap;
+//extern struct pagemap *kernel_pagemap;
 
-uintptr_t setup_user_stack(void)
+struct pagemap *create_user_pagemap(void)
+{
+    struct pagemap *pm = kmalloc(sizeof(struct pagemap));
+    if (!pm) {
+        printf("Failed to allocate user pagemap struct!\n");
+        return NULL;
+    }
+
+    spinlock_init(&pm->lock);
+
+    /* Allocate a fresh PML4 (physical page) */
+    pm->top_level = (uint64_t *)((uintptr_t)pmm_allocz(1) + MEM_PHYS_OFFSET);
+    if (!pm->top_level) {
+        printf("Failed to allocate user PML4!\n");
+        kfree(pm);
+        return NULL;
+    }
+
+    /* Copy kernel higher-half mappings (kernel + HHDM) */
+    for (size_t i = 256; i < 512; i++) {
+        pm->top_level[i] = kernel_pagemap->top_level[i];
+    }
+
+    /* Lower half remains zero (user address space) */
+    printf("[usermode] user pagemap created (PML4 phys = 0x%lx)\n",
+           (uint64_t)pm->top_level - MEM_PHYS_OFFSET);
+
+    return pm;
+}
+
+uintptr_t setup_user_stack(struct pagemap *pagemap)
 {
     user_stack_phys_base = (uint64_t)pmm_alloc(USER_STACK_PAGES);
 
@@ -37,7 +66,7 @@ uintptr_t setup_user_stack(void)
         uintptr_t virt = stack_bottom + i * PAGE_SIZE;
         uintptr_t phys = user_stack_phys_base + i * PAGE_SIZE;
 
-        if (!vmm_map_page(kernel_pagemap,
+        if (!vmm_map_page(pagemap,
                           virt,
                           phys,
                           PAGE_READ | PAGE_WRITE | PAGE_USER,
@@ -47,19 +76,13 @@ uintptr_t setup_user_stack(void)
             for (;;);
         }
 
-        // zero physical page through HHDM
-        //memset((void *)(phys + g_hhdm_offset), 0, PAGE_SIZE);
     }
 
     uintptr_t rsp = USER_STACK_TOP;
-
     rsp &= ~0xFULL;
-
     return rsp;
 }
 
-
-// usermode.c
 __attribute__((naked))
 void enter_user_mode(uint64_t rip, uint64_t rsp)
 {
@@ -98,21 +121,27 @@ void enter_user_mode(uint64_t rip, uint64_t rsp)
 
 void start_userspace(void)
 {
-    void *entry = NULL;
 
-    if (!ELF_Read("init.elf", &entry)) {
+    struct pagemap *user_pagemap = create_user_pagemap();
+    if (!user_pagemap) {
+        printf("Failed to create user pagemap\n");
+        for (;;);
+    }
+
+    void *elf_entry = NULL;
+    if (!ELF_Read("init.elf", &elf_entry, user_pagemap)) {
         printf("Failed to load init.elf\n");
         for(;;);
     }
 
-    if (!entry) {
+    if (!elf_entry) {
         printf("ELF has no entry point\n");
         for(;;);
     }
 
-    uintptr_t rsp = setup_user_stack();
+    uintptr_t user_rsp = setup_user_stack(user_pagemap);
 
-    printf("Entering usermode RIP=%p RSP=%p\n", entry, (void*)rsp);
+    printf("Entering usermode RIP=%p RSP=%p\n", elf_entry, (void*)user_rsp);
 
-    enter_user_mode((uint64_t)entry, (rsp & ~0xFULL));
+    sched_create_user_task("init", (uint64_t)elf_entry, user_rsp, user_pagemap);
 }

src/arch/x86_64/sys/pit.c

@@ -6,6 +6,7 @@
 #include "e9.h"
 #include "limine.h"
 #include "apic.h"
+#include "sched/scheduler.h"
 
 __attribute__((used, section(".limine_requests")))
 volatile struct limine_date_at_boot_request boot_request = {
@@ -39,7 +40,7 @@ void PIT_IRQ_Handler(Registers* regs)
         lapic_eoi();
     }
     
-    // You can add scheduler / time logic here later
+    sched_tick();
 }
 
 /* ========================= */