user program (still many #PF)

src/sched/process.c

@@ -4,6 +4,8 @@
  * @license GPL-3.0-only
  */
 
+#include "mem/paging.h"
+#include "mem/vmm.h"
 #include <stddef.h>
 #include <sched/process.h>
 #include <mem/kheap.h>
@@ -13,6 +15,7 @@
 #include <config.h>
 #include <io/serial/serial.h>
 #include <io/term/flanterm.h>
+#include <mem/utils.h>
 
 extern struct flanterm_context* ft_ctx;
 
@@ -196,4 +199,59 @@ void process_exit()
     for (;;) {
         asm("hlt");
     }
+}
+
+/*
+ * process_jump_to_user - Jump to userland
+ * @stack_top: Address of the top of the user stack
+ * @user_code: Address of the first instruction of user code
+ */
+void process_jump_to_user(uintptr_t stack_top, uintptr_t user_code)
+{
+    // 0x20 | 3 = 0x23 (user data segment | 3)
+    // 0x18 | 3 = 0x1B (user code segment | 3)
+    asm volatile(" \
+        push $0x23 \n\
+        push %0 \n\
+        push $0x202 \n\
+        push $0x1B \n\
+        push %1 \n\
+        iretq \n\
+        " :: "r"(stack_top), "r"(user_code));
+}
+
+// Kernel stack used for interrupts from userland process.
+// Should be set in TSS.RSP0 when switching to userland process.
+uint8_t interrupt_stack[0x8000];
+
+extern struct tss tss;
+
+/*
+ * process_create_user - Create a new user process
+ * @file: pointer to Limine file structure
+ *
+ * This function takes a loaded Limine executable
+ * module, and maps its code, a user stack, sets the
+ * TSS RSP0 for interrupts, and finally jumps to the
+ * user code.
+ */
+void process_create_user(struct limine_file* file)
+{
+    void* exec_addr = file->address;
+    uint64_t exec_size = file->size;
+
+    uint64_t* user_pml4 = vmm_create_address_space();
+    uintptr_t stack_top = vmm_alloc_user_stack(user_pml4);
+    uint64_t code = vmm_alloc_user_code(user_pml4, exec_addr, exec_size);
+    
+    // Could be kalloc_stack()ed PER PROCESS when we grow that
+    tss.rsp0 = (uint64_t)(interrupt_stack + sizeof(interrupt_stack));
+
+    // Load user_pml4 into cr3 along here??
+    load_cr3(VIRT_TO_PHYS((uint64_t)user_pml4));
+
+    // Copy code into user pages
+    memcpy((uint64_t*)code, exec_addr, exec_size);
+
+    process_jump_to_user(stack_top, code);
 }