Setup kernel stack; but process is failing

src/sched/process.c

@@ -11,10 +11,13 @@
 #include "string/string.h"
 #include "mem/gdt/gdt.h"
 #include "config.h"
+#include "io/serial/serial.h"
 
 struct process_t* processes_list;
 struct process_t* current_process;
 
+extern uint64_t *kernel_pml4;
+
 size_t next_free_pid = 0;
 
 void process_init()
@@ -52,14 +55,22 @@ struct process_t* process_create(char* name, void(*function)(void*), void* arg)
     proc->pid = next_free_pid++;
     proc->status = READY;
 
+    uint64_t* stack_top = (uint64_t*)kalloc_stack();
+    // push return address to the stack so when "ret" hits we jmp to exit instead of idk what
+    // stack grows DOWNWARDS!!
+    *(--stack_top) = (uint64_t)process_exit;
+
     proc->context = ctx;
     proc->context->iret_ss = KERNEL_DATA_SEGMENT; // process will live in kernel mode
-    proc->context->iret_rsp = (uint64_t)kalloc_stack();
+    proc->context->iret_rsp = (uint64_t)stack_top;
     proc->context->iret_flags = 0x202; //bit 2 and 9 set (Interrupt Flag)
     proc->context->iret_cs = KERNEL_CODE_SEGMENT;
     proc->context->iret_rip = (uint64_t)function; // beginning of executable code
     proc->context->rdi = (uint64_t)arg; // 1st arg is in rdi (as per x64 calling convention)
-    proc->context->rbp = 0;
+    proc->context->rbp = 0; 
+
+    // Kernel PML4 as it already maps code/stack (when switching to userland we'll have to change that)
+    proc->root_page_table = kernel_pml4;
 
     proc->next = 0;
 
@@ -126,4 +137,38 @@ struct process_t* process_get_next(struct process_t* process)
 {
     if (!process) return NULL;
     return process->next;
+}
+
+// (from gdt) This will switch tasks ONLY in ring 0
+// KERNEL CS = 0x08
+// KERNEL SS = 0x10
+__attribute__((naked, noreturn))
+void process_switch(uint64_t stack_addr, uint64_t code_addr)
+{
+    asm volatile(" \
+        push $0x10 \n\
+        push %0 \n\
+        push $0x202 \n\
+        push $0x08 \n\
+        push %1 \n\
+        iretq \n\
+        " :: "r"(stack_addr), "r"(code_addr));
+}
+
+
+// Will be used to clean up resources (if any, when we implement it)
+// Just mark as DEAD then idle. Scheduler will delete process at next timer interrupt % quantum.
+void process_exit()
+{
+    CLEAR_INTERRUPTS;
+    if (current_process)
+    {
+        current_process->status = DEAD;
+    }
+    SET_INTERRUPTS;
+    
+    for (;;)
+    {
+        asm("hlt");
+    }
 }

src/sched/process.h

@@ -9,6 +9,7 @@
 
 #include <stddef.h>
 #include "config.h"
+#include <stdint.h>
 
 typedef enum 
 {
@@ -33,6 +34,8 @@ struct process_t* process_create(char* name, void(*function)(void*), void* arg);
 void process_add(struct process_t** processes_list, struct process_t* process);
 void process_delete(struct process_t** processes_list, struct process_t* process);
 struct process_t* process_get_next(struct process_t* process);
+void process_switch(uint64_t stack_addr, uint64_t code_addr);
+void process_exit();
 
 void process_display_list(struct process_t* processes_list);
 

src/sched/scheduler.c

@@ -6,6 +6,8 @@
 
 #include "kernel.h"
 #include "process.h"
+#include "mem/paging/paging.h"
+#include <stdint.h>
 
 extern struct process_t* processes_list;
 extern struct process_t* current_process;
@@ -18,7 +20,7 @@ void scheduler_init()
 
 struct cpu_status_t* scheduler_schedule(struct cpu_status_t* context)
 {
-    current_process->context = context;
+    //current_process->context = context;
     current_process->status = READY;
 
     for (;;) {
@@ -41,6 +43,13 @@ struct cpu_status_t* scheduler_schedule(struct cpu_status_t* context)
         }
     }
     
-    DEBUG("current_process={pid=%u name='%s'}", current_process->pid, current_process->name);
+
+    // Current_process gets wrong context?? (iret_rip points to other stuff than process function; like putpixel() for example)
+    DEBUG("current_process={pid=%u, name='%s', root_page_table[virt]=%p}", current_process->pid, current_process->name, current_process->root_page_table);
+
+    load_cr3(VIRT_TO_PHYS((uint64_t)current_process->root_page_table));
+    DEBUG("loaded process pml4 into cr3");
+    /* process_switch(current_process->context->rbp, current_process->context->iret_rip);
+    DEBUG("switched to process rip!"); */
     return current_process->context;
 }

src/sched/scheduler.h

@@ -7,7 +7,7 @@
 #ifndef SCHEDULER_H
 #define SCHEDULER_H
 
-void scheduler_schedule();
+struct cpu_status_t* scheduler_schedule(struct cpu_status_t* context);
 void scheduler_init();
 
 #endif