[libc] Implement sbrk to allow malloc() to work

Userspace can now allocte via malloc. This is slightly janky because it
relies on a single static handle in the library code.

src/drivers/nulldrv/main.cpp

@@ -61,27 +61,17 @@ main(int argc, const char **argv)
 
 	_syscall_system_log("main thread starting");
 
-	uintptr_t base = 0xcc0000000;
-	j6_handle_t vma = j6_handle_invalid;
-	j6_status_t result = _syscall_vma_create_map(&vma, 0x100000, base, 1);
-	if (result != j6_status_ok)
-		return result;
-
-	size_t size = 0x800000;
-	result = _syscall_vma_resize(vma, &size);
-	if (result != j6_status_ok)
-		return result;
-
-	if (size == 0x800000)
-		_syscall_system_log("main thread resized memory area");
+	void *base = malloc(0x1000);
+	if (!base)
+		return 1;
 
 	uint64_t *vma_ptr = reinterpret_cast<uint64_t*>(base);
 	for (int i = 0; i < 300; ++i)
-		vma_ptr[i * 512] = uint64_t(i);
+		vma_ptr[i] = uint64_t(i);
 
 	_syscall_system_log("main thread wrote to memory area");
 
-	result = _syscall_endpoint_create(&endp);
+	j6_status_t result = _syscall_endpoint_create(&endp);
 	if (result != j6_status_ok)
 		return result;
 
@@ -94,7 +84,7 @@ main(int argc, const char **argv)
 	_syscall_system_log("main thread created sub thread");
 
 	char message[] = "MAIN THREAD SUCCESSFULLY CALLED SENDRECV IF THIS IS LOWERCASE";
-	size = sizeof(message);
+	size_t size = sizeof(message);
 	result = _syscall_endpoint_sendrecv(endp, &size, (void*)message);
 	if (result != j6_status_ok)
 		return result;

src/kernel/vm_space.cpp

@@ -71,6 +71,7 @@ vm_space::add(uintptr_t base, vm_area *area)
 	//TODO: check for collisions
 	m_areas.sorted_insert({base, area});
 	area->mapper().add(this);
+	area->handle_retain();
 	return true;
 }
 
@@ -81,6 +82,7 @@ vm_space::remove(vm_area *area)
 		if (a.area == area) {
 			m_areas.remove(a);
 			area->mapper().remove(this);
+			area->handle_release();
 			return true;
 		}
 	}

src/libraries/libc/include/j6libc/syscalls.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <j6/types.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif

src/libraries/libc/j6libc/sbrk.c

@@ -1,4 +1,39 @@
 #include <stdint.h>
-void *sbrk(intptr_t) __attribute__ ((weak));
+#include <j6/errors.h>
+#include <j6libc/syscalls.h>
+//void *sbrk(intptr_t) __attribute__ ((weak));
 
-void *sbrk(intptr_t i) { return 0; }
+static j6_handle_t __core_handle = 0;
+static intptr_t __core_size = 0;
+
+static const uintptr_t __core_base = 0x1c0000000;
+
+static const void *error_val = (void*)-1;
+
+void *sbrk(intptr_t i)
+{
+	if (i == 0)
+		return (void*)__core_base;
+
+	if (__core_size == 0) {
+		if (i < 0)
+			return (void*)-1;
+
+		j6_status_t result = _syscall_vma_create_map(&__core_handle, i, __core_base, 1);
+		if (result != j6_status_ok)
+			return (void*)-1;
+
+		__core_size = i;
+		return (void*)__core_base;
+	}
+
+	size_t new_size = __core_size + i;
+	j6_status_t result = _syscall_vma_resize(__core_handle, &new_size);
+	if (result != j6_status_ok)
+		return (void*)-1;
+
+	uintptr_t prev = __core_base + __core_size;
+	__core_size += i;
+
+	return (void*)prev;
+}