From f6bbebbee3c779971d12afeb12b115b5467ca9b2 Mon Sep 17 00:00:00 2001
From: Alexander Myltsev <a.myltsev@gmail.com>
Date: Mon, 21 Nov 2022 01:50:02 +0300
Subject: [PATCH] Add user/.

---
 Makefile     | 9 +++++++--
 user/crt.c   | 6 ++++++
 user/false.c | 3 +++
 3 files changed, 16 insertions(+), 2 deletions(-)
 create mode 100644 user/crt.c
 create mode 100644 user/false.c

diff --git a/Makefile b/Makefile
index 6333f8b..760de1a 100644
--- a/Makefile
+++ b/Makefile
@@ -27,15 +27,20 @@ debug: image.bin
 		-ex "break _start" \
 		-ex "continue"
 
-fs.img: kernel.bin tools/mkfs
+fs.img: kernel.bin tools/mkfs user/false
 	tools/mkfs $@ $<
 
+LDFLAGS=-m elf_i386
+
+user/%: user/%.o user/crt.o
+	$(LD) $(LDFLAGS) -o $@ -Ttext 0x101000 $^
+
 image.bin: mbr.bin fs.img
 	cat $^ >$@
 
 kernel.bin: kernel.o console.o drivers/vga.o drivers/keyboard.o \
 	string.o drivers/ata.o cpu/vectors.o cpu/idt.o drivers/uart.o
-	$(LD) -m elf_i386 -o $@ -Ttext 0x1000 $^
+	$(LD) $(LDFLAGS) -o $@ -Ttext 0x1000 $^
 
 %.o: %.c
 	$(CC) -m32 -ffreestanding -Wall -Werror -c -g $< -o $@
diff --git a/user/crt.c b/user/crt.c
new file mode 100644
index 0000000..1a42f40
--- /dev/null
+++ b/user/crt.c
@@ -0,0 +1,6 @@
+int main();
+
+void _start() {
+    int exit_status = main();
+    asm("int $0x84": :"a"(exit_status));
+}
diff --git a/user/false.c b/user/false.c
new file mode 100644
index 0000000..6346e2d
--- /dev/null
+++ b/user/false.c
@@ -0,0 +1,3 @@
+int main() {
+    return 1;
+}