feat(kernel): implement ELF64 loader, user space paging, and Ring 3 jump via iretq

2026-09-02 16:49:04 +03:00
parent 9cffb01889
commit 6cbd13b4aa
6 changed files with 281 additions and 25 deletions
@@ -0,0 +1,64 @@
+/* opencoreC - Ring 3 User Mode Transition (IRETQ) */
+.global enter_user_mode
+.extern set_kernel_stack
+
+.section .text
+/*
+ * void enter_user_mode(uint64_t entry_rip, uint64_t user_rsp, uint64_t pml4_paddr, uint64_t kernel_stack_top);
+ * RDI = entry_rip
+ * RSI = user_rsp
+ * RDX = pml4_paddr
+ * RCX = kernel_stack_top
+ */
+enter_user_mode:
+    /* 1. Save kernel stack in TSS (RSP0) for future interrupts/syscalls */
+    push rdi
+    push rsi
+    push rdx
+    mov rdi, rcx
+    call set_kernel_stack
+    pop rdx
+    pop rsi
+    pop rdi
+
+    /* 2. Switch to User Address Space (PML4) */
+    mov cr3, rdx
+
+    /* 3. Build IRETQ Stack Frame:
+     * [RSP + 32] = SS     (User Data: 0x18 | 3 = 0x1B)
+     * [RSP + 24] = RSP    (User Stack Pointer)
+     * [RSP + 16] = RFLAGS (Interrupt Flag Enabled: 0x202)
+     * [RSP + 8]  = CS     (User Code: 0x20 | 3 = 0x23)
+     * [RSP + 0]  = RIP    (User Entry Point)
+     */
+    mov ax, 0x1B
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+
+    push 0x1B          /* User SS */
+    push rsi           /* User RSP */
+    push 0x0202        /* RFLAGS (IF enabled) */
+    push 0x23          /* User CS */
+    push rdi           /* User RIP */
+
+    /* 4. Clear general-purpose registers */
+    xor rax, rax
+    xor rbx, rbx
+    xor rcx, rcx
+    xor rdx, rdx
+    xor rsi, rsi
+    xor rdi, rdi
+    xor rbp, rbp
+    xor r8,  r8
+    xor r9,  r9
+    xor r10, r10
+    xor r11, r11
+    xor r12, r12
+    xor r13, r13
+    xor r14, r14
+    xor r15, r15
+
+    /* 5. Jump to Ring 3 */
+    iretq