[kernel] Spit out vm_area types

The vm_space allow() functionality was a bit janky; using VMAs for all
regions would be a lot cleaner. To that end, this change:

- Adds a "static array" ctor to kutil::vector for setting the kernel
  address space's VMA list. This way a kernel heap VMA can be created
  without the heap already existing.
- Splits vm_area into different subclasses depending on desired behavior
- Splits out the concept of vm_mapper which maps vm_areas to vm_spaces,
  so that some kinds of VMA can be inherently single-space
- Implements VMA resizing so that userspace can grow allocations.
- Obsolete page_table_indices is removed

Also, the following bugs were fixed:

- kutil::map iterators on empty maps no longer break
- memory::page_count was doing page-align, not page-count

See: Github bug #242
See: [frobozz blog post](https://jsix.dev/posts/frobozz/)

Tags:

src/libraries/kutil/include/kutil/map.h

@@ -105,16 +105,19 @@ public:
 	}
 
 	iterator begin() {
+		if (!m_count) return iterator {0};
 		iterator it {m_nodes - 1, m_nodes + m_capacity};
 		return ++it;
 	}
 
 	const iterator begin() const {
+		if (!m_count) return iterator {0};
 		iterator it {m_nodes - 1, m_nodes + m_capacity};
 		return ++it;
 	}
 
 	const iterator end() const {
+		if (!m_count) return iterator {0};
 		return iterator(m_nodes + m_capacity);
 	}
 

src/libraries/kutil/include/kutil/vector.h

@@ -45,7 +45,7 @@ public:
 	}
 
 	/// Move constructor. Takes ownership of the other's array.
-	vector(vector&& other) :
+	vector(vector &&other) :
 		m_size(other.m_size),
 		m_capacity(other.m_capacity),
 		m_elements(other.m_elements)
@@ -55,6 +55,15 @@ public:
 		other.m_elements = nullptr;
 	}
 
+	/// Static array constructor. Starts the vector off with the given
+	/// static storage.
+	vector(T *data, size_t size, size_t capacity) :
+		m_size(size),
+		m_capacity(capacity),
+		m_elements(&data[0])
+	{
+	}
+
 	/// Destructor. Destroys any remaining items in the array.
 	~vector()
 	{

src/libraries/libc/arch/x86_64/syscalls.s

@@ -4,7 +4,11 @@
 		push rbp
 		mov rbp, rsp
 
-		; address of args should already be in rdi, etc
+		; args should already be in rdi, etc, but rcx will
+		; get stomped, so shift args out one spot from rcx
+		mov r9, r8
+		mov r8, rcx
+
 		mov rax, %2
 		syscall
 		; result is now already in rax, so just return
@@ -17,5 +21,7 @@
 %define SYSCALL(n, name, a) SYSCALL name, n
 %define SYSCALL(n, name, a, b) SYSCALL name, n
 %define SYSCALL(n, name, a, b, c) SYSCALL name, n
+%define SYSCALL(n, name, a, b, c, d) SYSCALL name, n
+%define SYSCALL(n, name, a, b, c, d, e) SYSCALL name, n
 
 %include "syscalls.inc"