From 41208c1e15eeffdf5f92af4b0a9655e134a22516 Mon Sep 17 00:00:00 2001
From: Paul Pan <i@0x7f.app>
Date: Sun, 16 Jun 2024 23:39:04 +0800
Subject: [PATCH] feat: root: add dummy root server

---
 Makefile        |  2 +-
 root/.gitignore |  3 +++
 root/Makefile   | 21 +++++++++++++++++++++
 root/link.ld    | 16 ++++++++++++++++
 root/root.S     | 19 +++++++++++++++++++
 5 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 root/.gitignore
 create mode 100644 root/Makefile
 create mode 100644 root/link.ld
 create mode 100644 root/root.S

diff --git a/Makefile b/Makefile
index 9ee62c0..78033f6 100644
--- a/Makefile
+++ b/Makefile
@@ -31,7 +31,7 @@ QEMU = qemu-system-$(ARCH)
 QEMU_ARGS  = -nographic -serial mon:stdio -smp 1
 QEMU_ARGS += -machine virt # TODO: override by $(BOARD)
 QEMU_ARGS += -kernel target/$(BUILD_TARGET)/$(MODE)/kernel
-QEMU_ARGS += -initrd build/init.cpio
+QEMU_ARGS += -initrd root/init.cpio
 QEMU_ARGS += -append "loglevel=4"
 
 kernel:
diff --git a/root/.gitignore b/root/.gitignore
new file mode 100644
index 0000000..584858d
--- /dev/null
+++ b/root/.gitignore
@@ -0,0 +1,3 @@
+*.cpio
+*.o
+root
diff --git a/root/Makefile b/root/Makefile
new file mode 100644
index 0000000..6b89509
--- /dev/null
+++ b/root/Makefile
@@ -0,0 +1,21 @@
+AS = riscv64-elf-as
+LD = riscv64-elf-ld
+
+ASFLAGS += -march=rv64imac -mabi=lp64
+
+.PHONY: all clean
+
+all: init.cpio
+
+%.o: %.S
+	$(AS) $(ASFLAGS) -c $< -o $@
+
+root: root.o
+	$(LD) -Tlink.ld $^ -o $@
+
+init.cpio: root
+	find . -type f -not -name "*.cpio" | cpio -ov -H crc > init.cpio
+
+clean:
+	rm -f *.o root
+	rm -f init.cpio
diff --git a/root/link.ld b/root/link.ld
new file mode 100644
index 0000000..6827996
--- /dev/null
+++ b/root/link.ld
@@ -0,0 +1,16 @@
+OUTPUT_ARCH(riscv)
+ENTRY(_start)
+
+PHDRS {
+    text   PT_LOAD FLAGS (5);
+    rodata PT_LOAD FLAGS (4);
+    data   PT_LOAD FLAGS (6);
+}
+
+SECTIONS {
+    . = 0x400000;
+    .text   : { *(.text   .text.*  ); . = ALIGN(4096); } : text
+    .rodata : { *(.rodata .rodata.*); . = ALIGN(4096); } : rodata
+    .data   : { *(.data   .data.*  ); . = ALIGN(4096); } : data
+    .bss    : { *(.bss    .bss.*   ); . = ALIGN(4096); } : data
+}
\ No newline at end of file
diff --git a/root/root.S b/root/root.S
new file mode 100644
index 0000000..095fa72
--- /dev/null
+++ b/root/root.S
@@ -0,0 +1,19 @@
+.macro syscall msg ptr
+	li	a0, \msg
+	li	a1, \ptr
+	ecall
+.endm
+
+.text
+	.global _start
+_start:
+	la	t0, msg
+.loop:
+	lb	a2, 0(t0)
+	beqz	a2, _start	# print forever
+	syscall (1<<12 | 1), 1	# see uapi/syscall.rs
+	addi	t0, t0, 1
+	j	.loop
+
+.data
+	msg : .string "Hello, world!\n\0"