[kernel] Add (wip) futex syscalls

Add the syscalls j6_futex_wait and j6_futex_wake. Currently marking this
as WIP as they need more testing.

Added to support futexes:
- vm_area and vm_space support for looking up physical address for a
  virtual address
- libj6 mutex implementation using futex system calls

src/kernel/objects/vm_area.cpp

@@ -86,7 +86,7 @@ vm_area_fixed::resize(size_t size)
 }
 
 bool
-vm_area_fixed::get_page(uintptr_t offset, uintptr_t &phys)
+vm_area_fixed::get_page(uintptr_t offset, uintptr_t &phys, bool alloc)
 {
     if (offset > m_size)
         return false;
@@ -106,11 +106,16 @@ vm_area_untracked::~vm_area_untracked()
 }
 
 bool
-vm_area_untracked::get_page(uintptr_t offset, uintptr_t &phys)
+vm_area_untracked::get_page(uintptr_t offset, uintptr_t &phys, bool alloc)
 {
     if (offset > m_size)
         return false;
 
+    if (!alloc) {
+        phys = 0;
+        return true;
+    }
+
     return frame_allocator::get().allocate(1, &phys);
 }
 
@@ -136,9 +141,12 @@ vm_area_open::~vm_area_open()
 }
 
 bool
-vm_area_open::get_page(uintptr_t offset, uintptr_t &phys)
+vm_area_open::get_page(uintptr_t offset, uintptr_t &phys, bool alloc)
 {
-    return page_tree::find_or_add(m_mapped, offset, phys);
+    if (alloc)
+        return page_tree::find_or_add(m_mapped, offset, phys);
+    else
+        return page_tree::find(m_mapped, offset, phys);
 }
 
 void
@@ -171,7 +179,7 @@ vm_area_guarded::return_section(uintptr_t addr)
 }
 
 bool
-vm_area_guarded::get_page(uintptr_t offset, uintptr_t &phys)
+vm_area_guarded::get_page(uintptr_t offset, uintptr_t &phys, bool alloc)
 {
     if (offset >= m_stacks.end())
         return false;
@@ -181,7 +189,7 @@ vm_area_guarded::get_page(uintptr_t offset, uintptr_t &phys)
     if ((offset >> 12) % m_pages == 0)
         return false;
 
-    return vm_area_open::get_page(offset, phys);
+    return vm_area_open::get_page(offset, phys, alloc);
 }
 
 vm_area_ring::vm_area_ring(size_t size, vm_flags flags) :
@@ -193,11 +201,11 @@ vm_area_ring::vm_area_ring(size_t size, vm_flags flags) :
 vm_area_ring::~vm_area_ring() {}
 
 bool
-vm_area_ring::get_page(uintptr_t offset, uintptr_t &phys)
+vm_area_ring::get_page(uintptr_t offset, uintptr_t &phys, bool alloc)
 {
     if (offset > m_bufsize)
         offset -= m_bufsize;
-    return vm_area_open::get_page(offset, phys);
+    return vm_area_open::get_page(offset, phys, alloc);
 }
 
 } // namespace obj

src/kernel/objects/vm_area.h

@@ -71,8 +71,10 @@ public:
     /// Get the physical page for the given offset
     /// \arg offset The offset into the VMA
     /// \arg phys   [out] Receives the physical page address, if any
+    /// \arg alloc  If true, and this is a valid address with no frame,
+    ///             allocate one if applicable
     /// \returns    True if there should be a page at the given offset
-    virtual bool get_page(uintptr_t offset, uintptr_t &phys) = 0;
+    virtual bool get_page(uintptr_t offset, uintptr_t &phys, bool alloc = true) = 0;
 
 protected:
     /// A VMA is not deleted until both no handles remain AND it's not
@@ -106,7 +108,7 @@ public:
     virtual ~vm_area_fixed();
 
     virtual size_t resize(size_t size) override;
-    virtual bool get_page(uintptr_t offset, uintptr_t &phys) override;
+    virtual bool get_page(uintptr_t offset, uintptr_t &phys, bool alloc = true) override;
 
 private:
     uintptr_t m_start;
@@ -124,7 +126,7 @@ public:
     vm_area_open(size_t size, vm_flags flags);
     virtual ~vm_area_open();
 
-    virtual bool get_page(uintptr_t offset, uintptr_t &phys) override;
+    virtual bool get_page(uintptr_t offset, uintptr_t &phys, bool alloc = true) override;
 
     /// Tell this VMA about an existing mapping that did not originate
     /// from get_page.
@@ -147,7 +149,7 @@ public:
     virtual ~vm_area_untracked();
 
     virtual bool add_to(vm_space *space) override;
-    virtual bool get_page(uintptr_t offset, uintptr_t &phys) override;
+    virtual bool get_page(uintptr_t offset, uintptr_t &phys, bool alloc = true) override;
 };
 
 
@@ -175,7 +177,7 @@ public:
     /// Return a section address to the available pool
     void return_section(uintptr_t addr);
 
-    virtual bool get_page(uintptr_t offset, uintptr_t &phys) override;
+    virtual bool get_page(uintptr_t offset, uintptr_t &phys, bool alloc = true) override;
 
 private:
     size_t m_pages;
@@ -196,7 +198,7 @@ public:
     vm_area_ring(size_t size, vm_flags flags);
     virtual ~vm_area_ring();
 
-    virtual bool get_page(uintptr_t offset, uintptr_t &phys) override;
+    virtual bool get_page(uintptr_t offset, uintptr_t &phys, bool alloc = true) override;
 
 private:
     size_t m_bufsize;