urt: Add user run-time library groundwork

Signed-off-by: Chloe M. <chloe@mensia.org>

service/urt/Makefile

@@ -0,0 +1,16 @@
+#
+# Copyright (c) 2026, Chloe M.
+# Provided under the BSD-3 clause
+#
+# Description:  User run-time build script
+# Author:       Chloe M.
+#
+
+include ../mk/user.mk
+
+.PHONY: urt
+urt: machine
+
+.PHONY: machine
+machine:
+	cd arch/$(PT_TARGET_ARCH)/; $(MAKE) $(PASSDOWN_ARGS)

service/urt/arch/amd64/Makefile

@@ -0,0 +1,18 @@
+#
+# Copyright (c) 2026, Chloe M.
+# Provided under the BSD-3 clause
+#
+# Description:  User run-time machdep build script
+# Author:       Chloe M.
+#
+
+ASMFILES = $(shell find . -name "*.S")
+ASMOFILES = $(ASMFILES:.S=.S.o)
+
+CFLAGS = $(SYS_CFLAGS)
+
+.PHONY: all
+all: $(ASMOFILES)
+
+%.S.o: %.S
+	$(SYS_CC) -c $< $(CFLAGS) -o $@

service/urt/arch/amd64/crt/crti.S

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: C-runtime entry
+ * Author:      Chloe M.
+ */
+
+    .text
+    .globl _start
+_start:
+    xor %rbp, %rbp  /* Terminate callstack */
+    call Main       /* Enter program main */
+1:  pause
+    jmp 1b

service/urt/dev/link.ld

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: User linker script
+ * Author:      Chloe M.
+ */
+
+ENTRY(_start)
+
+SECTIONS {
+    /* User programs live here */
+    . = 0x9000;
+
+    .text : {
+        *(.text .text.*)
+    }
+
+    .data : {
+        *(.data .data.*)
+    }
+
+    .bss : {
+        *(.bss .bss.*)
+        *(COMMON)
+    }
+
+    .rodata : {
+        *(.rodata .rodata.*)
+    }
+
+    /DISCARD/ : {
+        *(.eh_frame .eh_frame.*)
+        *(.note .note.*)
+    }
+}