Merge pull request #5 from redox-os/clone

Clone

arch/x86_64/src/acpi/mod.rs

@@ -43,6 +43,13 @@ pub fn init_sdt(sdt: &'static Sdt, active_table: &mut ActivePageTable) {
             println!("    XAPIC {}: {:>08X}", me, local_apic.address);
         }
 
+        let trampoline_frame = Frame::containing_address(PhysicalAddress::new(TRAMPOLINE));
+        let trampoline_page = Page::containing_address(VirtualAddress::new(TRAMPOLINE));
+
+        // Map trampoline
+        active_table.map_to(trampoline_page, trampoline_frame, entry::PRESENT | entry::WRITABLE);
+        active_table.flush(trampoline_page);
+
         for madt_entry in madt.iter() {
             println!("      {:?}", madt_entry);
             match madt_entry {
@@ -50,13 +57,6 @@ pub fn init_sdt(sdt: &'static Sdt, active_table: &mut ActivePageTable) {
                     println!("        This is my local APIC");
                 } else {
                     if ap_local_apic.flags & 1 == 1 {
-                        // Map trampoline
-                        {
-                            if active_table.translate_page(Page::containing_address(VirtualAddress::new(TRAMPOLINE))).is_none() {
-                                active_table.identity_map(Frame::containing_address(PhysicalAddress::new(TRAMPOLINE)), entry::PRESENT | entry::WRITABLE);
-                            }
-                        }
-
                         // Allocate a stack
                         // TODO: Allocate contiguous
                         let stack_start = allocate_frame().expect("no more frames in acpi stack_start").start_address().get();
@@ -128,6 +128,10 @@ pub fn init_sdt(sdt: &'static Sdt, active_table: &mut ActivePageTable) {
                 _ => ()
             }
         }
+
+        // Unmap trampoline
+        active_table.unmap(trampoline_page);
+        active_table.flush(trampoline_page);
     } else {
         println!(": Unknown");
     }
@@ -138,28 +142,43 @@ pub unsafe fn init(active_table: &mut ActivePageTable) -> Option<Acpi> {
     let start_addr = 0xE0000;
     let end_addr = 0xFFFFF;
 
-    // Map all of the ACPI table space
+    // Map all of the ACPI RSDP space
     {
         let start_frame = Frame::containing_address(PhysicalAddress::new(start_addr));
         let end_frame = Frame::containing_address(PhysicalAddress::new(end_addr));
         for frame in Frame::range_inclusive(start_frame, end_frame) {
-            if active_table.translate_page(Page::containing_address(VirtualAddress::new(frame.start_address().get()))).is_none() {
+            let page = Page::containing_address(VirtualAddress::new(frame.start_address().get()));
-                active_table.identity_map(frame, entry::PRESENT | entry::NO_EXECUTE);
+            active_table.map_to(page, frame, entry::PRESENT | entry::NO_EXECUTE);
-            }
+            active_table.flush(page);
         }
     }
 
     // Search for RSDP
     if let Some(rsdp) = RSDP::search(start_addr, end_addr) {
-        let get_sdt = |sdt_address: usize, active_table: &mut ActivePageTable| -> &'static Sdt {
+        let get_sdt = |sdt_address: usize, active_table: &mut ActivePageTable| -> (&'static Sdt, bool) {
-            if active_table.translate_page(Page::containing_address(VirtualAddress::new(sdt_address))).is_none() {
+            let mapped = if active_table.translate_page(Page::containing_address(VirtualAddress::new(sdt_address))).is_none() {
                 let sdt_frame = Frame::containing_address(PhysicalAddress::new(sdt_address));
-                active_table.identity_map(sdt_frame, entry::PRESENT | entry::NO_EXECUTE);
+                let sdt_page = Page::containing_address(VirtualAddress::new(sdt_address));
-            }
+                active_table.map_to(sdt_page, sdt_frame, entry::PRESENT | entry::NO_EXECUTE);
-            &*(sdt_address as *const Sdt)
+                active_table.flush(sdt_page);
+                true
+            } else {
+                false
+            };
+            (&*(sdt_address as *const Sdt), mapped)
         };
 
-        let rxsdt = get_sdt(rsdp.sdt_address(), active_table);
+        let drop_sdt = |sdt: &'static Sdt, mapped: bool, active_table: &mut ActivePageTable| {
+            let sdt_address = sdt as *const Sdt as usize;
+            drop(sdt);
+            if mapped {
+                let sdt_page = Page::containing_address(VirtualAddress::new(sdt_address));
+                active_table.unmap(sdt_page);
+                active_table.flush(sdt_page);
+            }
+        };
+
+        let (rxsdt, rxmapped) = get_sdt(rsdp.sdt_address(), active_table);
 
         for &c in rxsdt.signature.iter() {
             print!("{}", c as char);
@@ -167,21 +186,36 @@ pub unsafe fn init(active_table: &mut ActivePageTable) -> Option<Acpi> {
         println!(":");
         if let Some(rsdt) = Rsdt::new(rxsdt) {
             for sdt_address in rsdt.iter() {
-                let sdt = get_sdt(sdt_address, active_table);
+                let (sdt, mapped) = get_sdt(sdt_address, active_table);
                 init_sdt(sdt, active_table);
+                drop_sdt(sdt, mapped, active_table);
             }
         } else if let Some(xsdt) = Xsdt::new(rxsdt) {
             for sdt_address in xsdt.iter() {
-                let sdt = get_sdt(sdt_address, active_table);
+                let (sdt, mapped) = get_sdt(sdt_address, active_table);
                 init_sdt(sdt, active_table);
+                drop_sdt(sdt, mapped, active_table);
             }
         } else {
             println!("UNKNOWN RSDT OR XSDT SIGNATURE");
         }
+
+        drop_sdt(rxsdt, rxmapped, active_table);
     } else {
         println!("NO RSDP FOUND");
     }
 
+    // Unmap all of the ACPI RSDP space
+    {
+        let start_frame = Frame::containing_address(PhysicalAddress::new(start_addr));
+        let end_frame = Frame::containing_address(PhysicalAddress::new(end_addr));
+        for frame in Frame::range_inclusive(start_frame, end_frame) {
+            let page = Page::containing_address(VirtualAddress::new(frame.start_address().get()));
+            active_table.unmap(page);
+            active_table.flush(page);
+        }
+    }
+
     None
 }
 

arch/x86_64/src/context.rs

@@ -6,7 +6,7 @@ use core::sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, Ordering};
 /// This must be done, as no locks can be held on the stack during switch
 pub static CONTEXT_SWITCH_LOCK: AtomicBool = ATOMIC_BOOL_INIT;
 
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 pub struct Context {
     /// Page table pointer
     cr3: usize,

arch/x86_64/src/device/display.rs

@@ -3,7 +3,7 @@ use ransid::{Console, Event};
 use spin::Mutex;
 
 use memory::Frame;
-use paging::{ActivePageTable, PhysicalAddress, entry};
+use paging::{ActivePageTable, Page, PhysicalAddress, VirtualAddress, entry};
 
 #[cfg(target_arch = "x86_64")]
 #[allow(unused_assignments)]
@@ -95,14 +95,15 @@ pub unsafe fn init(active_table: &mut ActivePageTable) {
     if mode_info.physbaseptr > 0 {
         let width = mode_info.xresolution as usize;
         let height = mode_info.yresolution as usize;
-        let onscreen = mode_info.physbaseptr as usize;
+        let onscreen = mode_info.physbaseptr as usize + ::KERNEL_OFFSET;
         let size = width * height;
 
         {
-            let start_frame = Frame::containing_address(PhysicalAddress::new(onscreen));
+            let start_page = Page::containing_address(VirtualAddress::new(onscreen));
-            let end_frame = Frame::containing_address(PhysicalAddress::new(onscreen + size * 4 - 1));
+            let end_page = Page::containing_address(VirtualAddress::new(onscreen + size * 4 - 1));
-            for frame in Frame::range_inclusive(start_frame, end_frame) {
+            for page in Page::range_inclusive(start_page, end_page) {
-                active_table.identity_map(frame, /*actually sets PAT for write combining*/ entry::HUGE_PAGE | entry::PRESENT | entry::WRITABLE | entry::NO_EXECUTE);
+                let frame = Frame::containing_address(PhysicalAddress::new(page.start_address().get() - ::KERNEL_OFFSET));
+                active_table.map_to(page, frame, /*actually sets PAT for write combining*/ entry::HUGE_PAGE | entry::PRESENT | entry::WRITABLE | entry::NO_EXECUTE);
             }
         }
 
@@ -117,26 +118,8 @@ pub unsafe fn init(active_table: &mut ActivePageTable) {
         ));
         *CONSOLE.lock() = Some(Console::new(width/8, height/16));
     }
-}
 
-pub unsafe fn init_ap(active_table: &mut ActivePageTable) {
+    active_table.unmap(Page::containing_address(VirtualAddress::new(0x5200)));
-    active_table.identity_map(Frame::containing_address(PhysicalAddress::new(0x5200)), entry::PRESENT | entry::NO_EXECUTE);
-
-    let mode_info = &*(0x5200 as *const VBEModeInfo);
-    if mode_info.physbaseptr > 0 {
-        let width = mode_info.xresolution as usize;
-        let height = mode_info.yresolution as usize;
-        let start = mode_info.physbaseptr as usize;
-        let size = width * height;
-
-        {
-            let start_frame = Frame::containing_address(PhysicalAddress::new(start));
-            let end_frame = Frame::containing_address(PhysicalAddress::new(start + size * 4 - 1));
-            for frame in Frame::range_inclusive(start_frame, end_frame) {
-                active_table.identity_map(frame, /*actually sets PAT for write combining*/ entry::HUGE_PAGE | entry::PRESENT | entry::WRITABLE | entry::NO_EXECUTE);
-            }
-        }
-    }
 }
 
 /// A display

arch/x86_64/src/device/mod.rs

@@ -9,7 +9,3 @@ pub unsafe fn init(active_table: &mut ActivePageTable){
     display::init(active_table);
     ps2::init();
 }
-
-pub unsafe fn init_ap(active_table: &mut ActivePageTable) {
-    display::init_ap(active_table);
-}

arch/x86_64/src/interrupt/syscall.rs

@@ -3,7 +3,7 @@ pub unsafe extern fn syscall() {
     #[inline(never)]
     unsafe fn inner() {
         extern {
-            fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize) -> usize;
+            fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize, stack: usize) -> usize;
         }
 
         let mut a;
@@ -13,10 +13,11 @@ pub unsafe extern fn syscall() {
             let d;
             let e;
             let f;
-            asm!("" : "={rax}"(a), "={rbx}"(b), "={rcx}"(c), "={rdx}"(d), "={rsi}"(e), "={rdi}"(f)
+            let stack;
+            asm!("" : "={rax}"(a), "={rbx}"(b), "={rcx}"(c), "={rdx}"(d), "={rsi}"(e), "={rdi}"(f), "={rbp}"(stack)
                 : : : "intel", "volatile");
 
-            a = syscall(a, b, c, d, e, f);
+            a = syscall(a, b, c, d, e, f, stack);
         }
 
         asm!("" : : "{rax}"(a) : : "intel", "volatile");
@@ -36,3 +37,10 @@ pub unsafe extern fn syscall() {
         iretq"
         : : : : "intel", "volatile");
 }
+
+#[naked]
+pub unsafe extern fn clone_ret() -> usize {
+    asm!("pop rbp"
+        : : : : "intel", "volatile");
+        0
+}

arch/x86_64/src/lib.rs

@@ -22,7 +22,8 @@ pub extern crate x86;
 // Because the memory map is so important to not be aliased, it is defined here, in one place
 // The lower 256 PML4 entries are reserved for userspace
 // Each PML4 entry references up to 512 GB of memory
-// The upper 256 are reserved for the kernel
+// The top (511) PML4 is reserved for recursive mapping
+// The second from the top (510) PML4 is reserved for the kernel
     /// The size of a single PML4
     pub const PML4_SIZE: usize = 0x0000_0080_0000_0000;
 
@@ -33,7 +34,7 @@ pub extern crate x86;
     pub const KERNEL_OFFSET: usize = RECURSIVE_PAGE_OFFSET - PML4_SIZE;
 
     /// Offset to kernel heap
-    pub const KERNEL_HEAP_OFFSET: usize = KERNEL_OFFSET - PML4_SIZE;
+    pub const KERNEL_HEAP_OFFSET: usize = KERNEL_OFFSET + PML4_SIZE/2;
     /// Size of kernel heap
     pub const KERNEL_HEAP_SIZE: usize = 64 * 1024 * 1024; // 64 MB
 
@@ -43,14 +44,26 @@ pub extern crate x86;
     /// Size of kernel percpu variables
     pub const KERNEL_PERCPU_SIZE: usize = 64 * 1024; // 64 KB
 
+    /// Offset to user image
+    pub const USER_OFFSET: usize = 0;
+
     /// Offset to user heap
-    pub const USER_HEAP_OFFSET: usize = PML4_SIZE;
+    pub const USER_HEAP_OFFSET: usize = USER_OFFSET + PML4_SIZE;
 
     /// Offset to user stack
     pub const USER_STACK_OFFSET: usize = USER_HEAP_OFFSET + PML4_SIZE;
     /// Size of user stack
     pub const USER_STACK_SIZE: usize = 1024 * 1024; // 1 MB
 
+    /// Offset to user temporary image (used when cloning)
+    pub const USER_TMP_OFFSET: usize = USER_STACK_OFFSET + PML4_SIZE;
+
+    /// Offset to user temporary heap (used when cloning)
+    pub const USER_TMP_HEAP_OFFSET: usize = USER_TMP_OFFSET + PML4_SIZE;
+
+    /// Offset to user temporary stack (used when cloning)
+    pub const USER_TMP_STACK_OFFSET: usize = USER_TMP_HEAP_OFFSET + PML4_SIZE;
+
 
 /// Print to console
 #[macro_export]
@@ -126,7 +139,14 @@ macro_rules! interrupt_error {
             }
 
             // Push scratch registers
-            asm!("push rax
+            asm!("pop rax
+                pop rbx
+                pop rcx
+                pop rdx
+                pop rsi
+                pop rdi
+                hlt
+                push rax
                 push rcx
                 push rdx
                 push rdi

arch/x86_64/src/linker.ld

@@ -1,8 +1,8 @@
 ENTRY(kstart)
 OUTPUT_FORMAT(elf64-x86-64)
 
-/* KERNEL_OFFSET = 0xffffff0000100000; */
+KERNEL_OFFSET = 0xffffff0000100000;
-KERNEL_OFFSET = 0x100000;
+/* KERNEL_OFFSET = 0x100000; */
 
 SECTIONS {
     . = KERNEL_OFFSET;

arch/x86_64/src/paging/mapper.rs

@@ -63,8 +63,6 @@ impl Mapper {
 
     /// Unmap a page
     pub fn unmap(&mut self, page: Page) {
-        assert!(self.translate(page.start_address()).is_some());
-
         let p1 = self.p4_mut()
                      .next_table_mut(page.p4_index())
                      .and_then(|p3| p3.next_table_mut(page.p3_index()))
@@ -76,6 +74,18 @@ impl Mapper {
         deallocate_frame(frame);
     }
 
+    /// Unmap a page, return frame without free
+    pub fn unmap_return(&mut self, page: Page) -> Frame {
+        let p1 = self.p4_mut()
+                     .next_table_mut(page.p4_index())
+                     .and_then(|p3| p3.next_table_mut(page.p3_index()))
+                     .and_then(|p2| p2.next_table_mut(page.p2_index()))
+                     .expect("mapping code does not support huge pages");
+        let frame = p1[page.p1_index()].pointed_frame().unwrap();
+        p1[page.p1_index()].set_unused();
+        frame
+    }
+
     pub fn translate_page(&self, page: Page) -> Option<Frame> {
         self.p4().next_table(page.p4_index())
             .and_then(|p3| p3.next_table(page.p3_index()))

arch/x86_64/src/paging/mod.rs

@@ -22,6 +22,59 @@ pub const ENTRY_COUNT: usize = 512;
 /// Size of pages
 pub const PAGE_SIZE: usize = 4096;
 
+/// Setup page attribute table
+unsafe fn init_pat() {
+    let uncacheable = 0;
+    let write_combining = 1;
+    let write_through = 4;
+    //let write_protected = 5;
+    let write_back = 6;
+    let uncached = 7;
+
+    let pat0 = write_back;
+    let pat1 = write_through;
+    let pat2 = uncached;
+    let pat3 = uncacheable;
+
+    let pat4 = write_combining;
+    let pat5 = pat1;
+    let pat6 = pat2;
+    let pat7 = pat3;
+
+    msr::wrmsr(msr::IA32_PAT, pat7 << 56 | pat6 << 48 | pat5 << 40 | pat4 << 32
+                            | pat3 << 24 | pat2 << 16 | pat1 << 8 | pat0);
+}
+
+/// Copy tdata, clear tbss, set TCB self pointer
+unsafe fn init_tcb(cpu_id: usize) -> usize {
+    extern {
+        /// The starting byte of the thread data segment
+        static mut __tdata_start: u8;
+        /// The ending byte of the thread data segment
+        static mut __tdata_end: u8;
+        /// The starting byte of the thread BSS segment
+        static mut __tbss_start: u8;
+        /// The ending byte of the thread BSS segment
+        static mut __tbss_end: u8;
+    }
+
+    let tcb_offset;
+    {
+        let size = & __tbss_end as *const _ as usize - & __tdata_start as *const _ as usize;
+        let tbss_offset = & __tbss_start as *const _ as usize - & __tdata_start as *const _ as usize;
+
+        let start = ::KERNEL_PERCPU_OFFSET + ::KERNEL_PERCPU_SIZE * cpu_id;
+        let end = start + size;
+        tcb_offset = end - mem::size_of::<usize>();
+
+        ::externs::memcpy(start as *mut u8, & __tdata_start as *const u8, tbss_offset);
+        ::externs::memset((start + tbss_offset) as *mut u8, 0, size - tbss_offset);
+
+        *(tcb_offset as *mut usize) = end;
+    }
+    tcb_offset
+}
+
 /// Initialize paging
 ///
 /// Returns page table and thread control block offset
@@ -53,6 +106,8 @@ pub unsafe fn init(cpu_id: usize, stack_start: usize, stack_end: usize) -> (Acti
         static mut __bss_end: u8;
     }
 
+    init_pat();
+
     let mut active_table = ActivePageTable::new();
 
     let mut temporary_page = TemporaryPage::new(Page::containing_address(VirtualAddress::new(0x8_0000_0000)));
@@ -78,25 +133,23 @@ pub unsafe fn init(cpu_id: usize, stack_start: usize, stack_end: usize) -> (Acti
                 }
             }
 
-            let mut remap = |start: usize, end: usize, flags: EntryFlags| {
+            let mut remap = |start: usize, end: usize, flags: EntryFlags, offset: usize| {
                 if end > start {
                     let start_frame = Frame::containing_address(PhysicalAddress::new(start));
                     let end_frame = Frame::containing_address(PhysicalAddress::new(end - 1));
                     for frame in Frame::range_inclusive(start_frame, end_frame) {
-                        mapper.identity_map(frame.clone(), flags);
+                        let page = Page::containing_address(VirtualAddress::new(frame.start_address().get() + offset));
-
+                        mapper.map_to(page, frame, flags);
-                        //let page = Page::containing_address(VirtualAddress::new(frame.start_address().get() + ::KERNEL_OFFSET));
-                        //mapper.map_to(page, frame, flags);
                     }
                 }
             };
 
             // Remap stack writable, no execute
-            remap(stack_start, stack_end, PRESENT | NO_EXECUTE | WRITABLE);
+            remap(stack_start, stack_end, PRESENT | NO_EXECUTE | WRITABLE, 0);
 
             // Remap a section with `flags`
             let mut remap_section = |start: &u8, end: &u8, flags: EntryFlags| {
-                remap(start as *const _ as usize, end as *const _ as usize, flags);
+                remap(start as *const _ as usize - ::KERNEL_OFFSET, end as *const _ as usize - ::KERNEL_OFFSET, flags, ::KERNEL_OFFSET);
             };
             // Remap text read-only
             remap_section(& __text_start, & __text_end, PRESENT);
@@ -111,45 +164,71 @@ pub unsafe fn init(cpu_id: usize, stack_start: usize, stack_end: usize) -> (Acti
         }
     });
 
-    let uncacheable = 0;
-    let write_combining = 1;
-    let write_through = 4;
-    //let write_protected = 5;
-    let write_back = 6;
-    let uncached = 7;
-
-    let pat0 = write_back;
-    let pat1 = write_through;
-    let pat2 = uncached;
-    let pat3 = uncacheable;
-
-    let pat4 = write_combining;
-    let pat5 = pat1;
-    let pat6 = pat2;
-    let pat7 = pat3;
-
-    msr::wrmsr(msr::IA32_PAT, pat7 << 56 | pat6 << 48 | pat5 << 40 | pat4 << 32
-                            | pat3 << 24 | pat2 << 16 | pat1 << 8 | pat0);
-
     active_table.switch(new_table);
 
-    // Copy tdata, clear tbss, set TCB self pointer
+    (active_table, init_tcb(cpu_id))
-    let tcb_offset;
+}
+
+pub unsafe fn init_ap(cpu_id: usize, stack_start: usize, stack_end: usize, kernel_table: usize) -> (ActivePageTable, usize) {
+    extern {
+        /// The starting byte of the thread data segment
+        static mut __tdata_start: u8;
+        /// The ending byte of the thread data segment
+        static mut __tdata_end: u8;
+        /// The starting byte of the thread BSS segment
+        static mut __tbss_start: u8;
+        /// The ending byte of the thread BSS segment
+        static mut __tbss_end: u8;
+    }
+
+    init_pat();
+
+    let mut active_table = ActivePageTable::new();
+
+    let mut temporary_page = TemporaryPage::new(Page::containing_address(VirtualAddress::new(0x8_0000_0000)));
+
+    let mut new_table = {
+        let frame = allocate_frame().expect("no more frames in paging::init new_table");
+        InactivePageTable::new(frame, &mut active_table, &mut temporary_page)
+    };
+
+    active_table.with(&mut new_table, &mut temporary_page, |mapper| {
+        // Copy kernel mapping
+        let kernel_frame = Frame::containing_address(PhysicalAddress::new(kernel_table));
+        mapper.p4_mut()[510].set(kernel_frame, entry::PRESENT | entry::WRITABLE);
+
+        // Map tdata and tbss
         {
             let size = & __tbss_end as *const _ as usize - & __tdata_start as *const _ as usize;
-        let tbss_offset = & __tbss_start as *const _ as usize - & __tdata_start as *const _ as usize;
 
             let start = ::KERNEL_PERCPU_OFFSET + ::KERNEL_PERCPU_SIZE * cpu_id;
             let end = start + size;
-        tcb_offset = end - mem::size_of::<usize>();
 
-        ::externs::memcpy(start as *mut u8, & __tdata_start as *const u8, tbss_offset);
+            let start_page = Page::containing_address(VirtualAddress::new(start));
-        ::externs::memset((start + tbss_offset) as *mut u8, 0, size - tbss_offset);
+            let end_page = Page::containing_address(VirtualAddress::new(end - 1));
-
+            for page in Page::range_inclusive(start_page, end_page) {
-        *(tcb_offset as *mut usize) = end;
+                mapper.map(page, PRESENT | NO_EXECUTE | WRITABLE);
+            }
         }
 
-    (active_table, tcb_offset)
+        let mut remap = |start: usize, end: usize, flags: EntryFlags, offset: usize| {
+            if end > start {
+                let start_frame = Frame::containing_address(PhysicalAddress::new(start));
+                let end_frame = Frame::containing_address(PhysicalAddress::new(end - 1));
+                for frame in Frame::range_inclusive(start_frame, end_frame) {
+                    let page = Page::containing_address(VirtualAddress::new(frame.start_address().get() + offset));
+                    mapper.map_to(page, frame, flags);
+                }
+            }
+        };
+
+        // Remap stack writable, no execute
+        remap(stack_start, stack_end, PRESENT | NO_EXECUTE | WRITABLE, 0);
+    });
+
+    active_table.switch(new_table);
+
+    (active_table, init_tcb(cpu_id))
 }
 
 pub struct ActivePageTable {

arch/x86_64/src/start.rs

@@ -28,7 +28,7 @@ static mut TDATA_TEST_NONZERO: usize = 0xFFFFFFFFFFFFFFFF;
 
 pub static AP_READY: AtomicBool = ATOMIC_BOOL_INIT;
 static BSP_READY: AtomicBool = ATOMIC_BOOL_INIT;
-static HEAP_TABLE: AtomicUsize = ATOMIC_USIZE_INIT;
+static KERNEL_TABLE: AtomicUsize = ATOMIC_USIZE_INIT;
 
 extern {
     /// Kernel main function
@@ -65,7 +65,7 @@ pub unsafe extern fn kstart() -> ! {
         }
 
         // Initialize memory management
-        memory::init(0, &__end as *const u8 as usize);
+        memory::init(0, &__end as *const u8 as usize - ::KERNEL_OFFSET);
 
         // TODO: allocate a stack
         let stack_start = 0x00080000;
@@ -93,9 +93,9 @@ pub unsafe extern fn kstart() -> ! {
         // Reset AP variables
         AP_READY.store(false, Ordering::SeqCst);
         BSP_READY.store(false, Ordering::SeqCst);
-        HEAP_TABLE.store(0, Ordering::SeqCst);
+        KERNEL_TABLE.store(0, Ordering::SeqCst);
 
-        // Map heap
+        // Setup kernel heap
         {
             // Map heap pages
             let heap_start_page = Page::containing_address(VirtualAddress::new(::KERNEL_HEAP_OFFSET));
@@ -106,24 +106,26 @@ pub unsafe extern fn kstart() -> ! {
 
             // Init the allocator
             allocator::init(::KERNEL_HEAP_OFFSET, ::KERNEL_HEAP_SIZE);
+        }
 
-            // Send heap page table to APs
+        // Initialize devices
-            let index = heap_start_page.p4_index();
+        device::init(&mut active_table);
+
+        // Send kernel page table to APs
+        {
+            let index = Page::containing_address(VirtualAddress::new(::KERNEL_OFFSET)).p4_index();
 
             let p4 = active_table.p4();
             {
                 let entry = &p4[index];
                 if let Some(frame) = entry.pointed_frame() {
-                    HEAP_TABLE.store(frame.start_address().get(), Ordering::SeqCst);
+                    KERNEL_TABLE.store(frame.start_address().get(), Ordering::SeqCst);
                 } else {
-                    panic!("heap does not have PML4 entry");
+                    panic!("kernel does not have PML4 entry");
                 }
             }
         }
 
-        // Initialize devices
-        device::init(&mut active_table);
-
         // Read ACPI tables, starts APs
         acpi::init(&mut active_table);
 
@@ -139,8 +141,14 @@ pub unsafe extern fn kstart_ap(cpu_id: usize, page_table: usize, stack_start: us
         assert_eq!(BSS_TEST_ZERO, 0);
         assert_eq!(DATA_TEST_NONZERO, 0xFFFFFFFFFFFFFFFF);
 
+        // Retrieve kernel table entry
+        while KERNEL_TABLE.load(Ordering::SeqCst) == 0 {
+            interrupt::pause();
+        }
+        let kernel_table = KERNEL_TABLE.load(Ordering::SeqCst);
+
         // Initialize paging
-        let (mut active_table, tcb_offset) = paging::init(cpu_id, stack_start, stack_end);
+        let (mut active_table, tcb_offset) = paging::init_ap(cpu_id, stack_start, stack_end, kernel_table);
 
         // Set up GDT for AP
         gdt::init(tcb_offset, stack_end);
@@ -158,23 +166,6 @@ pub unsafe extern fn kstart_ap(cpu_id: usize, page_table: usize, stack_start: us
             assert_eq!(TDATA_TEST_NONZERO, 0xFFFFFFFFFFFFFFFE);
         }
 
-        // Copy heap PML4
-        {
-            while HEAP_TABLE.load(Ordering::SeqCst) == 0 {
-                interrupt::pause();
-            }
-            let frame = Frame::containing_address(PhysicalAddress::new(HEAP_TABLE.load(Ordering::SeqCst)));
-
-            let page = Page::containing_address(VirtualAddress::new(::KERNEL_HEAP_OFFSET));
-            let p4 = active_table.p4_mut();
-            let entry = &mut p4[page.p4_index()];
-            assert!(entry.is_unused());
-            entry.set(frame, entry::PRESENT | entry::WRITABLE);
-        }
-
-        // Init devices for AP
-        device::init_ap(&mut active_table);
-
         AP_READY.store(true, Ordering::SeqCst);
     }
 
@@ -201,7 +192,7 @@ pub unsafe fn usermode(ip: usize, sp: usize) -> ! {
         : // No output because it never returns
         :   "{rax}"(gdt::GDT_USER_DATA << 3 | 3), // Stack segment
             "{rbx}"(sp), // Stack pointer
-            "{rcx}"(3 << 12 | 1 << 9), // Flags - Set IOPL and interrupt enable flag
+            "{rcx}"(3 << 12/* | 1 << 9*/), // Flags - Set IOPL and interrupt enable flag
             "{rdx}"(gdt::GDT_USER_CODE << 3 | 3), // Code segment
             "{rsi}"(ip) // IP
         : // No clobers because it never returns

bootloader/x86_64/startup-x86_64.asm

@@ -126,6 +126,7 @@ long_mode:
 
     ;rust init
     mov rax, [kernel_base + 0x18]
+    xchg bx, bx
     jmp rax
 
 long_mode_ap:

bootloader/x86_64/vesa.asm

@@ -115,8 +115,8 @@ vesa:
 .minx dw 640
 .miny dw 480
 .required:
-.requiredx dw 0 ;1024    ;USE THESE WITH CAUTION
+.requiredx dw 1024    ;USE THESE WITH CAUTION
-.requiredy dw 0 ;768
+.requiredy dw 768
 .requiredmode dw 0
 
 .modeok db ": Is this OK?(y/n)",10,13,0

init/src/main.rs

@@ -1,4 +1,4 @@
-use std::{env, thread};
+use std::env;
 use std::fs::File;
 use std::io::{BufRead, BufReader};
 use std::process::Command;
@@ -47,8 +47,4 @@ pub fn main() {
             }
         }
     }
-
-    loop {
-        thread::yield_now();
-    }
 }

kernel/context/file.rs

@@ -1,6 +1,7 @@
 //! File struct
 
 /// A file
+//TODO: Close on exec
 #[derive(Copy, Clone, Debug)]
 pub struct File {
     /// The scheme that this file refers to

kernel/context/memory.rs

@@ -1,6 +1,7 @@
 use arch::externs::memset;
-use arch::paging::{ActivePageTable, Page, PageIter, VirtualAddress};
+use arch::paging::{ActivePageTable, InactivePageTable, Page, PageIter, VirtualAddress};
-use arch::paging::entry::EntryFlags;
+use arch::paging::entry::{self, EntryFlags};
+use arch::paging::temporary_page::TemporaryPage;
 
 #[derive(Debug)]
 pub struct Memory {
@@ -30,13 +31,17 @@ impl Memory {
         self.size
     }
 
+    pub fn flags(&self) -> EntryFlags {
+        self.flags
+    }
+
     pub fn pages(&self) -> PageIter {
         let start_page = Page::containing_address(self.start);
         let end_page = Page::containing_address(VirtualAddress::new(self.start.get() + self.size - 1));
         Page::range_inclusive(start_page, end_page)
     }
 
-    pub fn map(&mut self, flush: bool, clear: bool) {
+    fn map(&mut self, flush: bool, clear: bool) {
         let mut active_table = unsafe { ActivePageTable::new() };
 
         let mut flush_all = false;
@@ -56,12 +61,12 @@ impl Memory {
         }
 
         if clear {
-            assert!(flush);
+            assert!(flush && self.flags.contains(entry::WRITABLE));
             unsafe { memset(self.start_address().get() as *mut u8, 0, self.size); }
         }
     }
 
-    pub fn unmap(&mut self, flush: bool) {
+    fn unmap(&mut self, flush: bool) {
         let mut active_table = unsafe { ActivePageTable::new() };
 
         let mut flush_all = false;
@@ -80,6 +85,34 @@ impl Memory {
         }
     }
 
+    /// A complicated operation to move a piece of memory to a new page table
+    /// It also allows for changing the address at the same time
+    pub fn move_to(&mut self, new_start: VirtualAddress, new_table: &mut InactivePageTable, temporary_page: &mut TemporaryPage, flush: bool) {
+        let mut active_table = unsafe { ActivePageTable::new() };
+
+        let mut flush_all = false;
+
+        for page in self.pages() {
+            let frame = active_table.unmap_return(page);
+
+            active_table.with(new_table, temporary_page, |mapper| {
+                let new_page = Page::containing_address(VirtualAddress::new(page.start_address().get() - self.start.get() + new_start.get()));
+                mapper.map_to(new_page, frame, self.flags);
+            });
+
+            if flush {
+                //active_table.flush(page);
+                flush_all = true;
+            }
+        }
+
+        if flush_all {
+            active_table.flush_all();
+        }
+
+        self.start = new_start;
+    }
+
     pub fn remap(&mut self, new_flags: EntryFlags, flush: bool) {
         let mut active_table = unsafe { ActivePageTable::new() };
 

kernel/context/mod.rs

@@ -141,24 +141,40 @@ pub unsafe fn switch() {
 
     let mut to_ptr = 0 as *mut Context;
 
-    for (_pid, context_lock) in contexts().map.iter() {
+    for (pid, context_lock) in contexts().map.iter() {
+        if *pid > (*from_ptr).id {
             let mut context = context_lock.write();
             if ! context.running && ! context.blocked && ! context.exited {
                 to_ptr = context.deref_mut() as *mut Context;
                 break;
             }
         }
+    }
+
+    if to_ptr as usize == 0 {
+        for (pid, context_lock) in contexts().map.iter() {
+            if *pid < (*from_ptr).id {
+                let mut context = context_lock.write();
+                if ! context.running && ! context.blocked && ! context.exited {
+                    to_ptr = context.deref_mut() as *mut Context;
+                    break;
+                }
+            }
+        }
+    }
 
     if to_ptr as usize == 0 {
         // TODO: Sleep, wait for interrupt
         // Unset global lock if no context found
         arch::context::CONTEXT_SWITCH_LOCK.store(false, Ordering::SeqCst);
-        println!("No to_ptr");
         return;
     }
 
     (&mut *from_ptr).running = false;
     (&mut *to_ptr).running = true;
+    if let Some(ref stack) = (*to_ptr).kstack {
+        arch::gdt::TSS.rsp[0] = (stack.as_ptr() as usize + stack.len() - 256) as u64;
+    }
     CONTEXT_ID.store((&mut *to_ptr).id, Ordering::SeqCst);
 
     (&mut *from_ptr).arch.switch_to(&mut (&mut *to_ptr).arch);

kernel/elf.rs

@@ -55,8 +55,6 @@ impl<'a> Elf<'a> {
 
     /// Test function to run. Remove and replace with proper syscall
     pub fn run(self) -> SysResult<!> {
-        let stack_addr = arch::USER_STACK_OFFSET;
-        let stack_size = arch::USER_STACK_SIZE;
         {
             let contexts = context::contexts();
             let context_lock = contexts.current().ok_or(Error::NoProcess)?;
@@ -105,8 +103,8 @@ impl<'a> Elf<'a> {
 
             // Map stack
             context.stack = Some(context::memory::Memory::new(
-                VirtualAddress::new(stack_addr),
+                VirtualAddress::new(arch::USER_STACK_OFFSET),
-                stack_size,
+                arch::USER_STACK_SIZE,
                 entry::NO_EXECUTE | entry::WRITABLE | entry::USER_ACCESSIBLE,
                 true,
                 true
@@ -114,7 +112,7 @@ impl<'a> Elf<'a> {
         }
 
         // Go to usermode
-        unsafe { usermode(self.entry(), stack_addr + stack_size - 256); }
+        unsafe { usermode(self.entry(), arch::USER_STACK_OFFSET + arch::USER_STACK_SIZE - 256); }
     }
 }
 

kernel/lib.rs

@@ -100,6 +100,8 @@ extern crate bitflags;
 extern crate goblin;
 extern crate spin;
 
+use core::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT, Ordering};
+
 /// Context management
 pub mod context;
 
@@ -117,6 +119,14 @@ pub mod syscall;
 #[cfg(test)]
 pub mod tests;
 
+#[thread_local]
+static CPU_ID: AtomicUsize = ATOMIC_USIZE_INIT;
+
+#[inline(always)]
+pub fn cpu_id() -> usize {
+    CPU_ID.load(Ordering::Relaxed)
+}
+
 pub extern fn userspace_init() {
     assert_eq!(syscall::open(b"debug:", 0), Ok(0));
     assert_eq!(syscall::open(b"debug:", 0), Ok(1));
@@ -129,6 +139,8 @@ pub extern fn userspace_init() {
 
 #[no_mangle]
 pub extern fn kmain() {
+    CPU_ID.store(0, Ordering::SeqCst);
+
     context::init();
 
     let pid = syscall::getpid();
@@ -144,15 +156,19 @@ pub extern fn kmain() {
         }
     }
 
-    unsafe { context::switch(); }
-
     loop {
-        unsafe { interrupt::enable_and_halt(); }
+        unsafe {
+            interrupt::disable();
+            context::switch();
+            interrupt::enable_and_halt();
+        }
     }
 }
 
 #[no_mangle]
 pub extern fn kmain_ap(id: usize) {
+    CPU_ID.store(id, Ordering::SeqCst);
+
     context::init();
 
     let pid = syscall::getpid();

kernel/syscall/mod.rs

@@ -105,7 +105,10 @@ pub fn convert_slice_mut<T>(ptr: *mut T, len: usize) -> Result<&'static mut [T]>
     Ok(unsafe { slice::from_raw_parts_mut(ptr, len) })
 }
 
-pub fn handle(a: usize, b: usize, c: usize, d: usize, e: usize, _f: usize) -> Result<usize> {
+#[no_mangle]
+pub extern fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize, stack: usize) -> usize {
+    #[inline(always)]
+    fn inner(a: usize, b: usize, c: usize, d: usize, e: usize, _f: usize, stack: usize) -> Result<usize> {
         match Call::from(a) {
             Ok(call) => match call {
                 Call::Exit => exit(b),
@@ -118,7 +121,7 @@ pub fn handle(a: usize, b: usize, c: usize, d: usize, e: usize, _f: usize) -> Re
                 Call::Dup => dup(b),
                 Call::Brk => brk(b),
                 Call::Iopl => iopl(b),
-            Call::Clone => clone(b),
+                Call::Clone => clone(b, stack),
                 Call::SchedYield => sched_yield()
             },
             Err(err) => {
@@ -128,9 +131,7 @@ pub fn handle(a: usize, b: usize, c: usize, d: usize, e: usize, _f: usize) -> Re
         }
     }
 
-#[no_mangle]
+    match inner(a, b, c, d, e, f, stack) {
-pub extern fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize) -> usize {
-    match handle(a, b, c, d, e, f) {
         Ok(value) => value,
         Err(value) => (-(value as isize)) as usize
     }

kernel/syscall/process.rs

@@ -1,11 +1,15 @@
 ///! Process syscalls
 
+use core::mem;
 use core::str;
 
 use arch;
-use arch::paging::{VirtualAddress, entry};
+use arch::memory::allocate_frame;
+use arch::paging::{ActivePageTable, InactivePageTable, Page, VirtualAddress, entry};
+use arch::paging::temporary_page::TemporaryPage;
 use context;
 use elf;
+use scheme;
 use syscall::{self, Error, Result};
 
 pub fn brk(address: usize) -> Result<usize> {
@@ -42,9 +46,195 @@ pub fn brk(address: usize) -> Result<usize> {
     }
 }
 
-pub fn clone(flags: usize) -> Result<usize> {
+pub fn clone(flags: usize, stack_base: usize) -> Result<usize> {
-    println!("Clone {:X}", flags);
+    //TODO: Implement flags
-    Ok(0)
+    //TODO: Copy on write?
+    println!("Clone {:X}: {:X}", flags, stack_base);
+
+    let pid;
+    {
+        let arch;
+        let mut kstack_option = None;
+        let mut offset = 0;
+        let mut image = vec![];
+        let mut heap_option = None;
+        let mut stack_option = None;
+        let mut files = vec![];
+
+        // Copy from old process
+        {
+            let contexts = context::contexts();
+            let context_lock = contexts.current().ok_or(Error::NoProcess)?;
+            let context = context_lock.read();
+            arch = context.arch.clone();
+
+            if let Some(ref stack) = context.kstack {
+                offset = stack_base - stack.as_ptr() as usize - mem::size_of::<usize>(); // Add clone ret
+                let mut new_stack = stack.clone();
+                unsafe {
+                    let func_ptr = new_stack.as_mut_ptr().offset(offset as isize);
+                    *(func_ptr as *mut usize) = arch::interrupt::syscall::clone_ret as usize;
+                }
+                kstack_option = Some(new_stack);
+            }
+
+            for memory in context.image.iter() {
+                let mut new_memory = context::memory::Memory::new(
+                    VirtualAddress::new(memory.start_address().get() + arch::USER_TMP_OFFSET),
+                    memory.size(),
+                    entry::PRESENT | entry::NO_EXECUTE | entry::WRITABLE,
+                    true,
+                    false
+                );
+                unsafe {
+                    arch::externs::memcpy(new_memory.start_address().get() as *mut u8,
+                                          memory.start_address().get() as *const u8,
+                                          memory.size());
+                }
+                new_memory.remap(memory.flags(), true);
+                image.push(new_memory);
+            }
+
+            if let Some(ref heap) = context.heap {
+                let mut new_heap = context::memory::Memory::new(
+                    VirtualAddress::new(arch::USER_TMP_HEAP_OFFSET),
+                    heap.size(),
+                    entry::PRESENT | entry::NO_EXECUTE | entry::WRITABLE,
+                    true,
+                    false
+                );
+                unsafe {
+                    arch::externs::memcpy(new_heap.start_address().get() as *mut u8,
+                                          heap.start_address().get() as *const u8,
+                                          heap.size());
+                }
+                new_heap.remap(heap.flags(), true);
+                heap_option = Some(new_heap);
+            }
+
+            if let Some(ref stack) = context.stack {
+                let mut new_stack = context::memory::Memory::new(
+                    VirtualAddress::new(arch::USER_TMP_STACK_OFFSET),
+                    stack.size(),
+                    entry::PRESENT | entry::NO_EXECUTE | entry::WRITABLE,
+                    true,
+                    false
+                );
+                unsafe {
+                    arch::externs::memcpy(new_stack.start_address().get() as *mut u8,
+                                          stack.start_address().get() as *const u8,
+                                          stack.size());
+                }
+                new_stack.remap(stack.flags(), true);
+                stack_option = Some(new_stack);
+            }
+
+            for (fd, file_option) in context.files.iter().enumerate() {
+                if let Some(file) = *file_option {
+                    let result = {
+                        let schemes = scheme::schemes();
+                        let scheme_mutex = schemes.get(file.scheme).ok_or(Error::BadFile)?;
+                        let result = scheme_mutex.lock().dup(file.number);
+                        result
+                    };
+                    match result {
+                        Ok(new_number) => {
+                            files.push(Some(context::file::File { scheme: file.scheme, number: new_number }));
+                        },
+                        Err(err) => {
+                            println!("clone: failed to dup {}: {:?}", fd, err);
+                        }
+                    }
+                } else {
+                    files.push(None);
+                }
+            }
+        }
+
+        // Set up new process
+        {
+            let mut contexts = context::contexts_mut();
+            let context_lock = contexts.new_context()?;
+            let mut context = context_lock.write();
+
+            pid = context.id;
+
+            context.arch = arch;
+
+            let mut active_table = unsafe { ActivePageTable::new() };
+
+            let mut temporary_page = TemporaryPage::new(Page::containing_address(VirtualAddress::new(0x8_0000_0000)));
+
+            let mut new_table = {
+                let frame = allocate_frame().expect("no more frames in syscall::clone new_table");
+                InactivePageTable::new(frame, &mut active_table, &mut temporary_page)
+            };
+
+            // Copy kernel mapping
+            {
+                let kernel_frame = active_table.p4()[510].pointed_frame().expect("kernel table not mapped");
+                active_table.with(&mut new_table, &mut temporary_page, |mapper| {
+                    mapper.p4_mut()[510].set(kernel_frame, entry::PRESENT | entry::WRITABLE);
+                });
+            }
+
+            // Copy percpu mapping
+            {
+                extern {
+                    /// The starting byte of the thread data segment
+                    static mut __tdata_start: u8;
+                    /// The ending byte of the thread BSS segment
+                    static mut __tbss_end: u8;
+                }
+
+                let size = unsafe { & __tbss_end as *const _ as usize - & __tdata_start as *const _ as usize };
+
+                let start = arch::KERNEL_PERCPU_OFFSET + arch::KERNEL_PERCPU_SIZE * ::cpu_id();
+                let end = start + size;
+
+                let start_page = Page::containing_address(VirtualAddress::new(start));
+                let end_page = Page::containing_address(VirtualAddress::new(end - 1));
+                for page in Page::range_inclusive(start_page, end_page) {
+                    let frame = active_table.translate_page(page).expect("kernel percpu not mapped");
+                    active_table.with(&mut new_table, &mut temporary_page, |mapper| {
+                        mapper.map_to(page, frame, entry::PRESENT | entry::NO_EXECUTE | entry::WRITABLE);
+                    });
+                }
+            }
+
+
+            if let Some(stack) = kstack_option.take() {
+                context.arch.set_stack(stack.as_ptr() as usize + offset);
+                context.kstack = Some(stack);
+            }
+
+            for memory in image.iter_mut() {
+                let start = VirtualAddress::new(memory.start_address().get() - arch::USER_TMP_OFFSET + arch::USER_OFFSET);
+                memory.move_to(start, &mut new_table, &mut temporary_page, true);
+            }
+            context.image = image;
+
+            if let Some(mut heap) = heap_option.take() {
+                heap.move_to(VirtualAddress::new(arch::USER_HEAP_OFFSET), &mut new_table, &mut temporary_page, true);
+                context.heap = Some(heap);
+            }
+
+            if let Some(mut stack) = stack_option.take() {
+                stack.move_to(VirtualAddress::new(arch::USER_STACK_OFFSET), &mut new_table, &mut temporary_page, true);
+                context.stack = Some(stack);
+            }
+
+            context.files = files;
+
+            context.arch.set_page_table(unsafe { new_table.address() });
+
+            context.blocked = false;
+        }
+    }
+
+    unsafe { context::switch(); }
+
+    Ok(pid)
 }
 
 pub fn exit(status: usize) -> ! {
@@ -85,7 +275,9 @@ pub fn exec(path: &[u8], _args: &[[usize; 2]]) -> Result<usize> {
     let _ = syscall::close(file);
 
     match elf::Elf::from(&data) {
-        Ok(elf) => elf.run().and(Ok(0)),
+        Ok(elf) => {
+            elf.run().and(Ok(0))
+        },
         Err(err) => {
             println!("failed to execute {}: {}", unsafe { str::from_utf8_unchecked(path) }, err);
             Err(Error::NoExec)

syscall/src/lib.rs

@@ -110,7 +110,7 @@ pub fn chdir(path: &str) -> Result<usize> {
 }
 
 pub unsafe fn clone(flags: usize) -> Result<usize> {
-    syscall1(SYS_CLONE, flags)
+    syscall1_clobber(SYS_CLONE, flags)
 }
 
 pub fn close(fd: usize) -> Result<usize> {

syscall/src/x86.rs

@@ -20,6 +20,17 @@ pub unsafe fn syscall1(mut a: usize, b: usize) -> Result<usize> {
     Error::demux(a)
 }
 
+// Clobbers all registers - special for clone
+pub unsafe fn syscall1_clobber(mut a: usize, b: usize) -> Result<usize> {
+    asm!("int 0x80"
+        : "={eax}"(a)
+        : "{eax}"(a), "{ebx}"(b)
+        : "memory", "ebx", "ecx", "edx", "esi", "edi"
+        : "intel", "volatile");
+
+    Error::demux(a)
+}
+
 pub unsafe fn syscall2(mut a: usize, b: usize, c: usize) -> Result<usize> {
     asm!("int 0x80"
         : "={eax}"(a)

syscall/src/x86_64.rs

@@ -20,6 +20,17 @@ pub unsafe fn syscall1(mut a: usize, b: usize) -> Result<usize> {
     Error::demux(a)
 }
 
+// Clobbers all registers - special for clone
+pub unsafe fn syscall1_clobber(mut a: usize, b: usize) -> Result<usize> {
+    asm!("int 0x80"
+        : "={rax}"(a)
+        : "{rax}"(a), "{rbx}"(b)
+        : "memory", "rbx", "rcx", "rdx", "rsi", "rdi", "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
+        : "intel", "volatile");
+
+    Error::demux(a)
+}
+
 pub unsafe fn syscall2(mut a: usize, b: usize, c: usize) -> Result<usize> {
     asm!("int 0x80"
         : "={rax}"(a)