WIP: Support clone in userspace

Everything seems to work for the most part, but now there are tons of
daemons which rely on syscall::clone, which is now implemented in relibc
:(

src/context/arch/x86_64.rs

@@ -35,7 +35,7 @@ pub struct Context {
     /// Base pointer
     rbp: usize,
     /// Stack pointer
-    rsp: usize,
+    pub(crate) rsp: usize,
     /// FSBASE.
     ///
     /// NOTE: Same fsgsbase behavior as with gsbase.

src/context/context.rs

@@ -12,7 +12,7 @@ use core::{
 };
 use spin::RwLock;
 
-use crate::arch::{interrupt::InterruptStack, paging::PAGE_SIZE};
+use crate::arch::{interrupt::InterruptStack, paging::{PAGE_SIZE, RmmA, RmmArch}};
 use crate::common::unique::Unique;
 use crate::context::arch;
 use crate::context::file::{FileDescriptor, FileDescription};
@@ -250,6 +250,11 @@ pub struct Context {
     /// else than SIG_DFL, otherwise signals will not be delivered. Userspace is responsible for
     /// setting this.
     pub sigstack: Option<usize>,
+    /// An even hackier way to pass the return entry point and stack pointer to new contexts while
+    /// implementing clone. Before a context has returned to userspace, its IntRegisters cannot be
+    /// set since there is no interrupt stack (unless the kernel stack is copied, but that is in my
+    /// opinion hackier and less efficient than this (and UB to do in Rust)).
+    pub clone_entry: Option<[usize; 2]>,
 }
 
 // Necessary because GlobalAlloc::dealloc requires the layout to be the same, and therefore Box
@@ -352,6 +357,7 @@ impl Context {
             regs: None,
             ptrace_stop: false,
             sigstack: None,
+            clone_entry: None,
         };
         this.set_addr_space(new_addrspace()?.1);
         Ok(this)
@@ -528,8 +534,14 @@ impl Context {
         self.addr_space.as_ref().ok_or(Error::new(ESRCH))
     }
     pub fn set_addr_space(&mut self, addr_space: Arc<RwLock<AddrSpace>>) {
-        assert!(!self.running);
-        self.arch.set_page_utable(addr_space.read().frame.utable.start_address().data());
+        let physaddr = addr_space.read().frame.utable.start_address();
+        if self.running {
+            unsafe {
+                RmmA::set_table(physaddr);
+            }
+        }
+
+        self.arch.set_page_utable(physaddr.data());
         self.addr_space = Some(addr_space);
     }
 }

src/context/memory.rs

@@ -77,8 +77,7 @@ impl AddrSpace {
         // TODO: Abstract away this.
         let (mut inactive, mut active);
 
-        // TODO: aarch64
-        let mut this_mapper = if self.frame.utable.start_address().data() == unsafe { x86::controlregs::cr3() } as usize {
+        let mut this_mapper = if self.is_current() {
             active = unsafe { ActivePageTable::new(rmm::TableKind::User) };
             active.mapper()
         } else {
@@ -95,8 +94,8 @@ impl AddrSpace {
 
             for page in new_grant.pages() {
                 // FIXME: ENOMEM is wrong here, it cannot fail.
-                let current_frame = this_mapper.translate_page(page).ok_or(Error::new(ENOMEM))?.start_address().data() as *const u8;
-                let new_frame = new_mapper.mapper().translate_page(page).ok_or(Error::new(ENOMEM))?.start_address().data() as *mut u8;
+                let current_frame = unsafe { RmmA::phys_to_virt(this_mapper.translate_page(page).ok_or(Error::new(ENOMEM))?.start_address()) }.data() as *const u8;
+                let new_frame = unsafe { RmmA::phys_to_virt(new_mapper.mapper().translate_page(page).ok_or(Error::new(ENOMEM))?.start_address()) }.data() as *mut u8;
 
                 // TODO: Replace this with CoW
                 unsafe {
@@ -115,6 +114,9 @@ impl AddrSpace {
             id,
         })
     }
+    pub fn is_current(&self) -> bool {
+        self.frame.utable.start_address() == unsafe { RmmA::table() }
+    }
 }
 
 #[derive(Debug)]