15 files changed, 198 insertions, 0 deletions
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..83e9918
--- /dev/null
+++ b/README.md
@@ -0,0 +1,2 @@
+Experiments for `kernel`, `bios` and `init` taken from
+[@popovicu](https://github.com/popovicu) and his blog.
diff --git a/bios/Makefile b/bios/Makefile
new file mode 100644
index 0000000..60e3cc4
--- /dev/null
+++ b/bios/Makefile
@@ -0,0 +1,25 @@
+NAME = hello
+
+CROSS_AS 	?= riscv64-suse-linux-as
+CROSS_LD 	?= riscv64-suse-linux-ld
+CROSS_DUMP	?= riscv64-suse-linux-objdump
+ASFLAGS  	 = -march=rv64g -mabi=lp64
+
+EMU ?= qemu-system-riscv64
+
+##
+# Targets
+
+.PHONY: run
+run: clean build
+	$(CROSS_DUMP) -D $(NAME)
+	$(EMU) -machine virt -bios hello
+
+.PHONY: build
+build:
+	$(CROSS_AS) $(ASFLAGS) -o $(NAME).o -c $(NAME).s
+	$(CROSS_LD) -T config.ld $(NAME).o -o $(NAME)
+
+.PHONY: clean
+clean:
+	@rm -f $(NAME).o $(NAME)
diff --git a/bios/config.ld b/bios/config.ld
new file mode 100644
index 0000000..085caa3
--- /dev/null
+++ b/bios/config.ld
@@ -0,0 +1,9 @@
+MEMORY {
+  dram_space (rwx) : ORIGIN = 0x80000000, LENGTH = 128
+}
+
+SECTIONS {
+  .text : {
+    hello.o(.text.bios)
+  } > dram_space
+}
diff --git a/bios/hello.s b/bios/hello.s
new file mode 100644
index 0000000..f3aa20a
--- /dev/null
+++ b/bios/hello.s
@@ -0,0 +1,23 @@
+# From: https://github.com/qemu/qemu/blob/23fa74974d8c96bc95cbecc0d4e2d90f984939f6/hw/riscv/virt.c#L82.
+.set QEMU_UART0_ADDRESS, 0x10000000
+
+.global _start
+.section .text.bios
+
+_start:	li a0, 0x68
+	li a1, QEMU_UART0_ADDRESS
+	sb a0, (a1) # 'h'
+
+	li a0, 0x65
+	sb a0, (a1) # 'e'
+
+	li a0, 0x6C
+	sb a0, (a1) # 'l'
+
+	li a0, 0x6C
+	sb a0, (a1) # 'l'
+
+	li a0, 0x6F
+	sb a0, (a1) # 'o'
+
+loop:	j loop
diff --git a/init/Makefile b/init/Makefile
new file mode 100644
index 0000000..71405c3
--- /dev/null
+++ b/init/Makefile
@@ -0,0 +1,21 @@
+CROSS_CC 	?= riscv64-suse-linux-gcc
+CROSS_LD 	?= riscv64-suse-linux-ld
+CCFLAGS  	 = -static
+
+##
+# Targets
+
+.PHONY: hello
+hello: clean
+	$(CROSS_CC) $(CCFLAGS) -o init hello.c
+	cpio -o -H newc < file_list.txt > initramfs.cpio
+
+.PHONY: shell
+shell: clean
+	$(CROSS_CC) $(CCFLAGS) -o init shell.c
+	GOOS=linux GOARCH=riscv64 go build little_shell.go
+	cpio -o -H newc < file_list.txt > initramfs.cpio
+
+.PHONY: clean
+clean:
+	@rm -f *.o init initramfs.cpio
diff --git a/init/file_list.txt b/init/file_list.txt
new file mode 100644
index 0000000..9dd8872
--- /dev/null
+++ b/init/file_list.txt
@@ -0,0 +1,2 @@
+init
+little_shell
diff --git a/init/hello.c b/init/hello.c
new file mode 100644
index 0000000..d4e5892
--- /dev/null
+++ b/init/hello.c
@@ -0,0 +1,8 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+	printf("Hello, world!\n");
+	exit(0);
+}
diff --git a/init/little_shell b/init/little_shell
new file mode 100755
index 0000000..5e2446c
--- /dev/null
+++ b/init/little_shell
diff --git a/init/little_shell.go b/init/little_shell.go
new file mode 100644
index 0000000..7324323
--- /dev/null
+++ b/init/little_shell.go
@@ -0,0 +1,19 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+func main() {
+	fmt.Println("Hello world from Go!")
+
+	reader := bufio.NewReader(os.Stdin)
+
+	for {
+		fmt.Print("Enter your command: ")
+		line, _ := reader.ReadString('\n')
+		fmt.Printf("Your command is: %s", line)
+	}
+}
diff --git a/init/shell.c b/init/shell.c
new file mode 100644
index 0000000..d44b1c7
--- /dev/null
+++ b/init/shell.c
@@ -0,0 +1,32 @@
+#include <stdio.h>
+#include <unistd.h>
+
+int main(int argc, char *argv[])
+{
+	pid_t pid = fork();
+
+	if (pid == -1) {
+		printf("Unable to fork!");
+		return -1;
+	}
+
+	if (pid == 0) {
+		// This is a child process.
+		int status = execl("/little_shell", "irrelevant", NULL);
+
+		if (status == -1) {
+			printf("Forked process cannot start the little_shell");
+			return -2;
+		}
+	}
+
+	int count = 1;
+
+	while (1) {
+		printf("Hello from the original init! %d\n", count);
+		count++;
+		sleep(10);
+	}
+
+	return 0;
+}
diff --git a/kernel/Makefile b/kernel/Makefile
new file mode 100644
index 0000000..e943353
--- /dev/null
+++ b/kernel/Makefile
@@ -0,0 +1,20 @@
+CROSS_AS 	?= riscv64-suse-linux-as
+CROSS_LD 	?= riscv64-suse-linux-ld
+ASFLAGS  	 = -march=rv64g -mabi=lp64
+
+##
+# Targets
+
+.PHONY: infinite
+infinite: clean
+	$(CROSS_AS) $(ASFLAGS) -o infinite.o -c infinite.s
+	$(CROSS_LD) -T infinite.ld infinite.o -o infinite
+
+.PHONY: hello
+hello: clean
+	$(CROSS_AS) $(ASFLAGS) -o hello.o -c hello.s
+	$(CROSS_LD) -T hello.ld hello.o -o hello
+
+.PHONY: clean
+clean:
+	@rm -f *.o infinite hello
diff --git a/kernel/hello.ld b/kernel/hello.ld
new file mode 100644
index 0000000..e4af459
--- /dev/null
+++ b/kernel/hello.ld
@@ -0,0 +1,9 @@
+MEMORY {
+  kernel_space (rwx) : ORIGIN = 0x80200000, LENGTH = 128
+}
+
+SECTIONS {
+  .text : {
+    hello.o(.text.kernel)
+  } > kernel_space
+}
diff --git a/kernel/hello.s b/kernel/hello.s
new file mode 100644
index 0000000..eacd797
--- /dev/null
+++ b/kernel/hello.s
@@ -0,0 +1,15 @@
+.global _start
+.section .text.kernel
+
+_start: li a7, 0x4442434E
+        li a6, 0x00
+        li a0, 12
+        lla a1, debug_string
+        li a2, 0
+        ecall
+
+loop:   j loop
+
+        .section .rodata
+debug_string:
+        .string "Hello world\n"
diff --git a/kernel/infinite.ld b/kernel/infinite.ld
new file mode 100644
index 0000000..2eee384
--- /dev/null
+++ b/kernel/infinite.ld
@@ -0,0 +1,9 @@
+MEMORY {
+  kernel_space (rwx) : ORIGIN = 0x80200000, LENGTH = 128
+}
+
+SECTIONS {
+  .text : {
+    infinite.o(.text.kernel)
+  } > kernel_space
+}
diff --git a/kernel/infinite.s b/kernel/infinite.s
new file mode 100644
index 0000000..855f58e
--- /dev/null
+++ b/kernel/infinite.s
@@ -0,0 +1,4 @@
+	.global _start
+	.section .text.kernel
+
+_start:	j _start