From d4849c98408e8699e35da2eb0f13f747f17147c6 Mon Sep 17 00:00:00 2001
From: jenra-uwu <a>
Date: Sun, 25 Jul 2021 15:09:53 -0400
Subject: [PATCH] Initial commit

---
 .gitignore    |  1 +
 Makefile      | 13 +++++++++++++
 kernel.ld     | 44 ++++++++++++++++++++++++++++++++++++++++++++
 src/boot.s    | 17 +++++++++++++++++
 src/kernel.c  |  8 ++++++++
 src/opensbi.h | 28 ++++++++++++++++++++++++++++
 src/opensbi.s | 26 ++++++++++++++++++++++++++
 7 files changed, 137 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 kernel.ld
 create mode 100644 src/boot.s
 create mode 100644 src/kernel.c
 create mode 100644 src/opensbi.h
 create mode 100644 src/opensbi.s

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..533e957
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+kernel
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..6d5f23a
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,13 @@
+CODE=src/
+CC=riscv64-unknown-elf-gcc
+CFLAGS=-march=rv64gc -mabi=lp64d -static -mcmodel=medany -fvisibility=hidden -nostdlib -nostartfiles -Tkernel.ld -g -Wall -Wextra
+EMU=qemu-system-riscv64
+EFLAGS=-machine virt -cpu rv64 -bios opensbi-riscv64-generic-fw_dynamic.bin -m 256m -nographic -global virtio-mmio.force-legacy=false -s #-S
+
+.PHONY: all clean run
+
+all: $(CODE)*.s $(CODE)*.c
+	$(CC) $(CFLAGS) $? -o kernel
+	  
+run:
+	$(EMU) $(EFLAGS) -kernel kernel
diff --git a/kernel.ld b/kernel.ld
new file mode 100644
index 0000000..cb22f19
--- /dev/null
+++ b/kernel.ld
@@ -0,0 +1,44 @@
+OUTPUT_ARCH( "riscv" )
+OUTPUT_FORMAT( "elf64-littleriscv" )
+ENTRY( _start )
+SECTIONS
+{
+    /* text: text code section */
+    . = 0x80200000;
+    PROVIDE(text_start = .);
+    .text : { *(.text) }
+
+    /* data: Initialized data segment */
+    .gnu_build_id : { *(.note.gnu.build-id) }
+
+    . = ALIGN(4096);
+    PROVIDE(data_start = .);
+    .data : { *(.data) }
+
+    . = ALIGN(4096);
+    PROVIDE(ro_data_start = .);
+    .rodata : { *(.rodata) }
+
+    . = ALIGN(4096);
+    PROVIDE(sdata_start = .);
+    .sdata : { *(.sdata) }
+    .debug : { *(.debug) }
+
+    . = ALIGN(4096);
+    PROVIDE(stack_start = .);
+    . += 0x4000;
+    PROVIDE(stack_top = .);
+
+    /* Heap */
+    . = ALIGN(4096);
+    PROVIDE(heap_bottom = .);
+    . += 0x80000;
+
+    /* Pages */
+    . = ALIGN(4096);
+    PROVIDE(pages_bottom = .);
+
+    /* End of uninitalized data segement */
+}
+
+
diff --git a/src/boot.s b/src/boot.s
new file mode 100644
index 0000000..77a4aaf
--- /dev/null
+++ b/src/boot.s
@@ -0,0 +1,17 @@
+.section .text
+.global _start
+
+# a0 - current hart id
+# a1 - pointer to flattened device tree
+
+_start:
+	# Initialise stack pointer
+
+	la sp, stack_top
+	mv fp, sp
+
+	j kinit
+
+finish:
+	j finish
+
diff --git a/src/kernel.c b/src/kernel.c
new file mode 100644
index 0000000..fd21f8d
--- /dev/null
+++ b/src/kernel.c
@@ -0,0 +1,8 @@
+#include "opensbi.h"
+
+void kinit(unsigned long long hartid, void* fdt) {
+	sbi_console_putchar('a');
+
+	while(1);
+}
+
diff --git a/src/opensbi.h b/src/opensbi.h
new file mode 100644
index 0000000..0f44661
--- /dev/null
+++ b/src/opensbi.h
@@ -0,0 +1,28 @@
+#ifndef OPENSBI_H
+#define OPENSBI_H
+
+enum {
+	SBIRET_ERROR_CODE_SUCCESS               =  0,
+	SBIRET_ERROR_CODE_FAILED                = -1,
+	SBIRET_ERROR_CODE_UNSUPPORTED           = -2,
+	SBIRET_ERROR_CODE_INVALID_PARAMETER     = -3,
+	SBIRET_ERROR_CODE_DENIED                = -4,
+	SBIRET_ERROR_CODE_INVALID_ADDRESS       = -5,
+	SBIRET_ERROR_CODE_ALREADY_AVAILABLE     = -6
+};
+
+struct sbiret {
+	unsigned long error;
+	unsigned long value;
+};
+
+// sbi_console_putchar(char) -> void
+// Puts a character onto the UART port.
+void sbi_console_putchar(char);
+
+// sbi_console_getchar() -> int
+// Puts a character onto the UART port.
+int sbi_console_getchar();
+
+#endif /* OPENSBI_H */
+
diff --git a/src/opensbi.s b/src/opensbi.s
new file mode 100644
index 0000000..15d497d
--- /dev/null
+++ b/src/opensbi.s
@@ -0,0 +1,26 @@
+.section .text
+
+.global sbi_console_putchar
+.global sbi_console_getchar
+
+# EIDs are stored in a7
+# FIDs are stored in a6
+
+# sbi_console_putchar(char) -> void
+# Puts a character onto the UART port.
+
+sbi_console_putchar:
+	li a6, 0
+	li a7, 1
+	ecall
+	ret
+
+# sbi_console_getchar() -> int
+# Gets a character from the UART port.
+
+sbi_console_getchar:
+	li a6, 0
+	li a7, 2
+	ecall
+	ret
+