refactor(mm): rework how map_kernel is defined

src/mm/init.zig

@@ -4,17 +4,14 @@ const mm = r.mm;
 const mi = mm.private;
 const config = @import("config");
 
-const is_um = @hasDecl(config, "CONFIG_ARCH_UM");
-
-pub const map_kernel = if (!is_um)
-    struct {
 extern var text_start_addr: u8;
 extern var text_end_addr: u8;
 extern var rodata_start_addr: u8;
 extern var rodata_end_addr: u8;
 extern var data_start_addr: u8;
 extern var data_end_addr: u8;
-        pub fn call(boot_info: *pl.BootInfo) void {
+
+fn map_kernel(boot_info: *pl.BootInfo) void {
     const kaddr = boot_info.kernel_address;
 
     const text_start = @intFromPtr(&text_start_addr);
@@ -31,6 +28,7 @@ pub const map_kernel = if (!is_um)
     const start_phys = kaddr.physical_base;
     const start_virt = kaddr.virtual_base;
     const until_size = text_start - start_virt;
+
     mi.kernel_pmap.map_contiguous_range(start_virt, start_phys, until_size, .{
         .read = true,
         .write = true,
@@ -90,15 +88,12 @@ pub const map_kernel = if (!is_um)
         });
     }
 }
-    }.call
-else
-    struct {
-        pub fn call(_: *pl.BootInfo) void {}
-    }.call;
 
 pub fn init(boot_info: *pl.BootInfo) linksection(r.init) void {
     mi.phys.init(boot_info);
+    if (!@hasDecl(config, "CONFIG_ARCH_UM")) {
         map_kernel(boot_info);
+    }
     mi.kernel_pmap.activate();
     mi.phys.init_pfndb();
     mi.zone.early_init();