implemented user mode

kernel.c

@@ -4,6 +4,7 @@
 extern char __bss[], __bss_end[], __stack_top[];
 extern char __free_ram[], __free_ram_end[];
 extern char __kernel_base[];
+extern char _binary_shell_bin_start[], _binary_shell_bin_size[];
 
 struct process procs[PROCS_MAX];
 struct process *current_proc;
@@ -190,7 +191,19 @@ __attribute__((naked)) void switch_context(uint32_t *prev_sp,
     );
 }
 
-struct process *create_process(uint32_t pc) {
+__attribute__((naked)) void user_entry(void) {
+    __asm__ __volatile__(
+        "csrw sepc, %[sepc]         \n"
+        "csrw sstatus, %[sstatus]   \n"
+        "sret                       \n"
+        :
+        : [sepc] "r" (USER_BASE),
+          [sstatus] "r" (SSTATUS_SPIE)
+    );
+}
+
+
+struct process *create_process(const void *image, size_t image_size) {
     // Find an unused proccess control structure
     struct process *proc = NULL;
     int i;
@@ -218,7 +231,7 @@ struct process *create_process(uint32_t pc) {
     *--sp = 0;                    // s2
     *--sp = 0;                    // s1
     *--sp = 0;                    // s0
-    *--sp = (uint32_t) pc;        // ra
+    *--sp = (uint32_t) user_entry;        // ra (changed)
     
     // Map kernel pages
     uint32_t *page_table = (uint32_t *) alloc_pages(1);
@@ -226,6 +239,20 @@ struct process *create_process(uint32_t pc) {
         map_page(page_table, paddr, paddr, PAGE_R | PAGE_W | PAGE_X);
     }
 
+    // Map user pages
+    for (uint32_t off = 0; off < image_size; off += PAGE_SIZE) {
+        paddr_t page = alloc_pages(1);
+
+        // Case where data to be copied is smaller than the page size
+        size_t remaining = image_size - off;
+        size_t copy_size = PAGE_SIZE <= remaining ? PAGE_SIZE : remaining;
+    
+        // Fill and map the page
+        memcpy((void *) page, image + off, copy_size);
+        map_page(page_table, USER_BASE + off, page,
+                 PAGE_U | PAGE_R | PAGE_W | PAGE_X);
+    }
+
     // Initialize fields
     proc->pid = i + 1;
     proc->state = PROC_RUNNABLE;
@@ -304,7 +331,7 @@ void kernel_main(void) {
 
     WRITE_CSR(stvec, (uint32_t) kernel_entry);
 
-    idle_proc = create_process((uint32_t) NULL);
+    idle_proc = create_process(NULL, 0);
     idle_proc->pid = 0; // idle
     current_proc = idle_proc;
 
@@ -313,8 +340,11 @@ void kernel_main(void) {
     // printf("alloc_pages test paddr0=%x\n", paddr0);
     // printf("alloc_pages test paddr1=%x\n", paddr1);
 
-    proc_a = create_process((uint32_t) proc_a_entry);
-    proc_b = create_process((uint32_t) proc_b_entry);
+    // proc_a = create_process((uint32_t) proc_a_entry);
+    // proc_b = create_process((uint32_t) proc_b_entry);
+
+    // NEW
+    create_process(_binary_shell_bin_start, (size_t) _binary_shell_bin_size);
 
     yield();
     PANIC("Switched to idle process");

kernel.h

@@ -10,6 +10,8 @@
 #define PAGE_W (1 << 2) // Writable
 #define PAGE_X (1 << 3) // Executable
 #define PAGE_U (1 << 4) // User (accessible in user mode)
+#define USER_BASE 0x1000000
+#define SSTATUS_SPIE (1 << 5)
 
 struct process {
     int pid;                    // ID of a process

shell.c

@@ -1,5 +1,17 @@
 #include "user.h"
 
 void main(void) {
+    // *((volatile int *) 0x80200000) = 0x1234;
+    // printf("      ___           ___           ___           ___           ___       ___           ___     \\n");
+    // printf("     /\\  \\         /\\__\\         /\\  \\         /\\  \\         /\\__\\     /\\  \\         /\\  \\    \\n");
+    // printf("    /::\\  \\       /::|  |       /::\\  \\       /::\\  \\       /:/  /    /::\\  \\       /::\\  \\   \\n");
+    // printf("   /:/\\:\\  \\     /:|:|  |      /:/\\:\\  \\     /:/\\:\\  \\     /:/  /    /:/\\:\\  \\     /:/\\ \\  \\  \\n");
+    // printf("  /::\\~\\:\\  \\   /:/|:|__|__   /:/  \\:\\  \\   /::\\~\\:\\  \\   /:/  /    /:/  \\:\\  \\   _\\:\\~\\ \\  \\ \\n");
+    // printf(" /:/\\:\\ \\:\\__\\ /:/ |::::\\__\\ /:/__/ \\:\\__\\ /:/\\:\\ \\:\\__\\ /:/__/    /:/__/ \\:\\__\\ /\\ \\:\\ \\ \\__\\\\n");
+    // printf(" \\/__\\:\\/:/  / \\/__/~~/:/  / \\:\\  \\ /:/  / \\:\\~\\:\\ \\/__/ \\:\\  \\    \\:\\  \\ /:/  / \\:\\ \\:\\ \\/__/\\n");
+    // printf("      \\::/  /        /:/  /   \\:\\  /:/  /   \\:\\ \\:\\__\\    \\:\\  \\    \\:\\  /:/  /   \\:\\ \\:\\__\\  \\n");
+    // printf("      /:/  /        /:/  /     \\:\\/:/  /     \\:\\ \\/__/     \\:\\  \\    \\:\\/:/  /     \\:\\/:/  /  \\n");
+    // printf("     /:/  /        /:/  /       \\::/  /       \\:\\__\\        \\:\\__\\    \\::/  /       \\::/  /   \\n");
+    // printf("     \\/__/         \\/__/         \\/__/         \\/__/         \\/__/     \\/__/         \\/__/    \\n");
     for (;;);
 }

user.ld

@@ -1,7 +1,7 @@
 ENTRY(start)
 
 SECTIONS {
-    . = 0x10000000;
+    . = 0x1000000;
 
     /* machine code */
     .text :{