build: add a "user" arch to allow the kernel to run as a program on the host machine

arch/user/init.c

@@ -0,0 +1,68 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <socks/init.h>
+#include <socks/memblock.h>
+#include <socks/vm.h>
+#include <socks/object.h>
+#include <socks/printk.h>
+#include <arch/stdcon.h>
+#include <sys/mman.h>
+
+#define PMEM_SIZE 0x2000000
+
+extern void kernel_init(uintptr_t arg);
+
+static void *pmem = NULL;
+
+static void early_vm_init(void)
+{
+	pmem = mmap(NULL, PMEM_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (pmem == MAP_FAILED) {
+		fprintf(stderr, "arch: cannot map physical memory buffer.");
+		abort();
+	}
+	
+	uintptr_t alloc_start = (uintptr_t)pmem + VM_PAGE_SIZE;
+	uintptr_t alloc_end = alloc_start + PMEM_SIZE;
+
+	memblock_init(alloc_start, alloc_end, (uintptr_t)pmem);
+	printk("memblock: allocating from [0x%llx-0x%llx]", alloc_start, alloc_end);
+}
+
+uintptr_t __pagemap_base(void)
+{
+	return (uintptr_t)pmem;
+}
+
+uintptr_t __pagemap_limit(void)
+{
+	return (uintptr_t)pmem + PMEM_SIZE - 1;
+}
+
+int ml_init(uintptr_t arg)
+{
+	stdcon_init();
+	print_kernel_banner();
+	early_vm_init();
+
+	memblock_add(0, PMEM_SIZE);
+
+	vm_zone_descriptor_t vm_zones[] = {
+		{ .zd_id = VM_ZONE_DMA, .zd_node = 0, .zd_name = "dma", .zd_base = 0x00, .zd_limit = 0xffffff },
+		{ .zd_id = VM_ZONE_NORMAL, .zd_node = 0, .zd_name = "normal", .zd_base = 0x1000000, .zd_limit = UINTPTR_MAX },
+	};
+
+	vm_bootstrap(vm_zones, sizeof vm_zones / sizeof vm_zones[0]);
+
+	object_bootstrap();
+	return 0;
+}
+
+int main(int argc, const char **argv)
+{
+	kernel_init(0);
+
+	munmap(pmem, PMEM_SIZE);
+	return 0;
+}