urt: Add user run-time library groundwork

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

service/dev/build.env

@@ -13,6 +13,8 @@
 export PT_PROJECT_ROOT=$PT_PROJECT_ROOT
 export PT_TARGET_ARCH=$PT_TARGET_ARCH
 export PT_BOOT_PROTO=$PT_BOOT_PROTO
+export PT_URT_LIB=$PT_URT_LIB
+export PT_URT_CRT=$PT_URT_CRT
 
 if [ "$PT_BUILD_SOURCED" != "1" ]
 then

service/dev/bvars.env

@@ -9,3 +9,5 @@
 PT_PROJECT_ROOT=$(pwd)
 PT_TARGET_ARCH=amd64
 PT_BOOT_PROTO=limine
+PT_URT_LIB=$PT_PROJECT_ROOT/service/urt/
+PT_URT_CRT=$PT_PROJECT_ROOT/service/urt/arch/$PT_TARGET_ARCH

service/mk/user.mk

@@ -0,0 +1,51 @@
+#
+# Copyright (c) 2026, Chloe M.
+# Provided under the BSD-3 clause
+#
+# Description:  User build flags, etc
+# Author:       Chloe M.
+#
+
+.SILENT:
+PROMPT := printf "%s\t\t%s\n"
+
+ifeq ($(PT_TARGET_ARCH), amd64)
+	CC_TARGET = x86_64-unknown-elf
+else
+	CC_TARGET =
+endif
+
+CC =	\
+	clang
+ld =	\
+	ld
+
+SYS_CFLAGS =			\
+	-nostdlib			\
+	-nostdinc			\
+	-ffreestanding		\
+	-fexceptions		\
+	-target $(CC_TARGET)\
+	-Wno-attributes		\
+	-Wno-multichar		\
+	-fno-stack-protector\
+	-I$(PT_PROJECT_ROOT)/sdk/head
+
+ifeq ($(PT_TARGET_ARCH),amd64)
+	SYS_CFLAGS += 		\
+		-mno-sse		\
+		-mno-sse2		\
+		-mno-sse3		\
+		-mno-avx		\
+		-mno-avx2		\
+		-mno-80387		\
+		-mno-3dnow		\
+		-mno-mmx
+endif
+
+PASSDOWN_ARGS = \
+	ARCH=$(PT_TARGET_ARCH)		\
+	SYS_CC=$(CC)				\
+	SYS_LD=$(LD)				\
+	SYS_CFLAGS="$(SYS_CFLAGS)"	\
+	USER_LDS=$(PT_PROJECT_ROOT)/service/urt/dev/link.ld

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.*)
+    }
+}