Load a very simple ELF and launch it in usermode

arch/x86_64/src/idt.rs

@@ -60,6 +60,7 @@ pub unsafe fn init() {
 
     // Set syscall function
     IDT[0x80].set_func(syscall::syscall);
+    IDT[0x80].set_flags(IDT_PRESENT | IDT_RING_3 | IDT_INTERRUPT);
 
     dtables::lidt(&IDTR);
 }

arch/x86_64/src/interrupt/syscall.rs

@@ -1,22 +1,29 @@
 #[naked]
 pub unsafe extern fn syscall() {
-    extern {
-        fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize) -> usize;
+    #[inline(never)]
+    unsafe fn inner() {
+        extern {
+            fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize) -> usize;
+        }
+
+        let mut a;
+        {
+            let b;
+            let c;
+            let d;
+            let e;
+            let f;
+            asm!("xchg bx, bx" : "={rax}"(a), "={rbx}"(b), "={rcx}"(c), "={rdx}"(d), "={rsi}"(e), "={rdi}"(f)
+                : : : "intel", "volatile");
+
+            a = syscall(a, b, c, d, e, f);
+        }
+
+        asm!("xchg bx, bx" : : "{rax}"(a) : : "intel", "volatile");
     }
 
-    let a;
-    let b;
-    let c;
-    let d;
-    let e;
-    let f;
-    asm!("" : "={rax}"(a), "={rbx}"(b), "={rcx}"(c), "={rdx}"(d), "={rsi}"(e), "={rdi}"(f)
-        : : : "intel", "volatile");
+    inner();
 
-    let a = syscall(a, b, c, d, e, f);
-
-    asm!("" : : "{rax}"(a) : : "intel", "volatile");
-
-    // Pop scratch registers, error code, and return
+    // Interrupt return
     asm!("iretq" : : : : "intel", "volatile");
 }

arch/x86_64/src/lib.rs

@@ -17,7 +17,7 @@ extern crate hole_list_allocator as allocator;
 extern crate bitflags;
 extern crate ransid;
 extern crate spin;
-extern crate x86;
+pub extern crate x86;
 
 /// Print to console
 #[macro_export]

arch/x86_64/src/paging/mapper.rs

@@ -46,6 +46,15 @@ impl Mapper {
         self.map_to(page, frame, flags)
     }
 
+    /// Update flags for a page
+    pub fn remap(&mut self, page: Page, flags: EntryFlags) {
+        let mut p3 = self.p4_mut().next_table_mut(page.p4_index()).expect("failed to remap: no p3");
+        let mut p2 = p3.next_table_mut(page.p3_index()).expect("failed to remap: no p2");
+        let mut p1 = p2.next_table_mut(page.p2_index()).expect("failed to remap: no p1");
+        let frame = p1[page.p1_index()].pointed_frame().expect("failed to remap: not mapped");
+        p1[page.p1_index()].set(frame, flags | entry::PRESENT);
+    }
+
     /// Identity map a frame
     pub fn identity_map(&mut self, frame: Frame, flags: EntryFlags) {
         let page = Page::containing_address(VirtualAddress::new(frame.start_address().get()));

arch/x86_64/src/paging/table.rs

@@ -66,7 +66,7 @@ impl<L> Table<L> where L: HierarchicalLevel {
             assert!(!self[index].flags().contains(HUGE_PAGE),
                     "mapping code does not support huge pages");
             let frame = allocate_frame().expect("no frames available");
-            self[index].set(frame, PRESENT | WRITABLE);
+            self[index].set(frame, PRESENT | WRITABLE | USER_ACCESSIBLE /* Allow users to go down the page table, implement permissions at the page level */);
             self.next_table_mut(index).unwrap().zero();
         }
         self.next_table_mut(index).unwrap()

arch/x86_64/src/start.rs

@@ -137,28 +137,6 @@ pub unsafe extern fn kstart() -> ! {
     kmain();
 }
 
-unsafe fn usermode(ip: usize, sp: usize) {
-    // Test usermode
-    asm!("xchg bx, bx
-        mov rax, 0x2B
-        mov ds, ax
-        mov es, ax
-        mov fs, ax
-        mov gs, ax
-
-        push rax
-        push rbx
-        pushfq
-        mov rax, 0x23
-        push rax
-        push rcx
-        iretq"
-        :
-        : "{rbx}"(sp), "{rcx}"(ip)
-        : "rax", "rbx", "rcx", "sp"
-        : "intel", "volatile");
-}
-
 /// Entry to rust for an AP
 pub unsafe extern fn kstart_ap(stack_start: usize, stack_end: usize) -> ! {
     {
@@ -223,3 +201,25 @@ pub unsafe extern fn kstart_ap(stack_start: usize, stack_end: usize) -> ! {
 
     kmain_ap(ap_number);
 }
+
+pub unsafe fn usermode(ip: usize, sp: usize) {
+    // Test usermode
+    asm!("xchg bx, bx
+        mov rax, 0x2B
+        mov ds, ax
+        mov es, ax
+        mov fs, ax
+        mov gs, ax
+
+        push rax
+        push rbx
+        pushfq
+        mov rax, 0x23
+        push rax
+        push rcx
+        iretq"
+        :
+        : "{rbx}"(sp), "{rcx}"(ip)
+        : "rax", "rbx", "rcx", "sp"
+        : "intel", "volatile");
+}