refactor(readme): update

.clang-format

@@ -0,0 +1,8 @@
+BasedOnStyle: LLVM
+UseTab: Always
+TabWidth: 4
+IndentWidth: 4
+IndentCaseLabels: true
+ColumnLimit: 120
+PointerAlignment: Right
+AllowShortFunctionsOnASingleLine: None

.clangd

@@ -0,0 +1,2 @@
+Completion:
+  HeaderInsertion: Never

.gitignore

@@ -1,3 +1,13 @@
+/disk/*
+!/disk/.gitkeep
+*.map
+*.tar
+*.o
+*.elf
+*.bin
+*.log
+*.pcap
+
 # ---> C
 # Prerequisites
 *.d
@@ -51,4 +61,3 @@ modules.order
 Module.symvers
 Mkfile.old
 dkms.conf
-

README.md

@@ -1,2 +1,5 @@
 # rivos
 
+A small educational operating system targeting the RISC-V architecture.
+
+Focused on simplicity, low-level exploration, and learning by building.

format.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+set -xue
+
+find . -type f -name '*.c' -exec clang-format -i {} \;
+find . -type f -name '*.h' -exec clang-format -i {} \;

include/io.h

@@ -0,0 +1,14 @@
+#ifndef RIVOS_IO_H
+#define RIVOS_IO_H
+
+#include "../include/types.h"
+
+#define va_list __builtin_va_list
+#define va_start __builtin_va_start
+#define va_end __builtin_va_end
+#define va_arg __builtin_va_arg
+
+void r_printf(const char *fmt, ...);
+size_t r_strlen(const char *str);
+
+#endif

include/kernel.h

@@ -0,0 +1,9 @@
+#ifndef RIVOS_KERNEL_H
+#define RIVOS_KERNEL_H
+
+typedef struct sbiret_s {
+	long error;
+	long value;
+} sbiret_s;
+
+#endif

include/types.h

@@ -0,0 +1,11 @@
+#ifndef RIVOS_TYPES_H
+#define RIVOS_TYPES_H
+
+/**
+ * Define our standard types
+ */
+typedef unsigned char u8;
+typedef unsigned int u32;
+typedef u32 size_t;
+
+#endif

kernel.ld

@@ -0,0 +1,59 @@
+/**
+ * This is the entry point
+ * `boot` should be a defined label
+ */
+ENTRY(boot)
+
+/**
+ * SECTIONS tells to linker how to arrange sections inside the memory
+ */
+SECTIONS {
+    /**
+     * This is the base address (start address of the kernel)
+     * OpenSBI takes little ram
+     */
+    . = 0x80200000;
+
+    /**
+     * This section contains the code of the program
+     */
+    .text :{
+        /**
+         * Take the .text.boot before everything
+         * KEEP() prevents the linker to mark it as "unused"
+         */
+        KEEP(*(.text.boot));
+        /**
+         * Include everything else inside the .text section
+         */
+        *(.text .text.*);
+    }
+
+    /**
+     * Contains constant read-only data
+     * Align the start of the section at 4 byte
+     */
+    .rodata : ALIGN(4) {
+        *(.rodata .rodata.*);
+    }
+
+    /**
+     * Contains read/write data
+     */
+    .data : ALIGN(4) {
+        *(.data .data.*);
+    }
+
+    /**
+     * Contains read/data with an initial value of zero
+     */
+    .bss : ALIGN(4) {
+        __bss = .;
+        *(.bss .bss.* .sbss .sbss.*);
+        __bss_end = .;
+    }
+
+    . = ALIGN(4);
+    . += 128 * 1024; /* 128KB */
+    __stack_top = .;
+}

run.sh

@@ -0,0 +1,32 @@
+#!/bin/bash
+
+# -x -> trace: print every command
+# -u -> exit if undefined variables are used
+# -e -> exit if an error occurs
+set -xue
+
+QEMU=qemu-system-riscv32
+
+# Compile
+CC=clang
+# -ffreestanding: do not use stdlib of the host environment
+# -fuse-ld=lld: LLVM linker
+# -fno-stack-protector: disable stack protection
+# -Wl,-Tkernel.ld: linker script
+# -Wl,-Map=kernel.map: output a map file (linker allocationr result)
+CFLAGS="-std=c11 -O2 -g3 -Wall -Wextra --target=riscv32-unknown-elf -fuse-ld=lld -fno-stack-protector -ffreestanding -nostdlib"
+
+$CC $CFLAGS -Wl,-Tkernel.ld -Wl,-Map=kernel.map -o kernel.elf \
+    src/kernel.c \
+    src/io.c
+
+# Run QEMU
+# -machine virt: generic riscv platform
+# -bios default: load the default firmware (OpenSBI)
+# -nographic: disable VGA, everything on console
+# -serial mon:stdio: serial port is connected to terminal's stdin/stdout
+# --no-reboot: do not reboot if there's panic/shutdown/crash
+$QEMU -machine virt -bios default -nographic -serial mon:stdio --no-reboot \
+    -kernel kernel.elf
+
+# Press Ctrl+A and then C to enter QEMU debug console and quit with `q`

src/io.c

@@ -0,0 +1,100 @@
+#include "../include/io.h"
+
+void k_putchar(char ch);
+
+void r_printf(const char *fmt, ...) {
+	va_list args;
+	va_start(args, fmt);
+
+	while (*fmt) {
+		if (*fmt != '%') {
+			k_putchar(*fmt);
+			fmt++;
+			continue;
+		}
+
+		/* Skip '%' */
+		fmt++;
+		switch (*fmt) {
+			case '\0': {
+				/* Simply print the char */
+				k_putchar('%');
+
+				goto end;
+			}
+			case '%': {
+				/* Print '%' */
+				k_putchar('%');
+
+				break;
+			}
+			case 's': {
+				/* Print a NULL-terminated string */
+				const char *s = va_arg(args, const char *);
+				while (*s) {
+					k_putchar(*s);
+					s++;
+				}
+
+				break;
+			}
+			case 'd': {
+				/* Print an integer in decimal */
+				int value = va_arg(args, int);
+				unsigned magnitude = value;
+				if (value < 0) {
+					k_putchar('-');
+					magnitude = -magnitude;
+				}
+
+				unsigned divisor = 1;
+				while (magnitude / divisor > 9) {
+					divisor *= 10;
+				}
+
+				while (divisor > 0) {
+					k_putchar('0' + magnitude);
+					k_putchar('0' + magnitude / divisor);
+					magnitude %= divisor;
+					k_putchar('0' + magnitude);
+					divisor /= 10;
+					k_putchar('0' + magnitude);
+				}
+
+				break;
+			}
+			case 'x': {
+				/* Print an integer in hexadecimal */
+				unsigned value = va_arg(args, unsigned);
+				for (int i = 7; i >= 0; --i) {
+					unsigned nibble = (value >> (i * 4)) & 0xF;
+					/* From a char array we get the nibble position */
+					k_putchar("0123456789ABCDEF"[nibble]);
+				}
+			}
+			default: {
+				const char *str = "NOT IMPLEMENTED";
+				size_t len = r_strlen(str);
+				for (size_t i = 0; i < len; ++i) {
+					k_putchar(str[i]);
+				}
+			}
+		}
+
+		/* Next char */
+		fmt++;
+	}
+end:
+	va_end(args);
+}
+
+size_t r_strlen(const char *str) {
+	size_t len = 0;
+
+	while (*str) {
+		len++;
+		str++;
+	}
+
+	return len;
+}

src/kernel.c

@@ -0,0 +1,74 @@
+#include "../include/kernel.h"
+#include "../include/io.h"
+#include "../include/types.h"
+
+extern char __bss[], __bss_end[], __stack_top[];
+
+/**
+ * This function will call OpenSBI
+ * ecall is used as the control transfer instruction,
+ * it switches from kernel mode (s-mode) to opensbi mode (m-mode)
+ * a7 encodes the SBI extension ID (EID)
+ * a6 encodes the SBI function ID (FID)
+ *
+ * a0 returns and error code
+ */
+sbiret_s sbi_call(long arg0, long arg1, long arg2, long arg3, long arg4, long arg5, long fid, long eid) {
+	register long a0 __asm("a0") = arg0;
+	register long a1 __asm__("a1") = arg1;
+	register long a2 __asm__("a2") = arg2;
+	register long a3 __asm__("a3") = arg3;
+	register long a4 __asm__("a4") = arg4;
+	register long a5 __asm__("a5") = arg5;
+	register long a6 __asm__("a6") = fid;
+	register long a7 __asm__("a7") = eid;
+
+	__asm__ __volatile__("ecall"
+						 : "=r"(a0), "=r"(a1)
+						 : "r"(a0), "r"(a1), "r"(a2), "r"(a3), "r"(a4), "r"(a5), "r"(a6), "r"(a7)
+						 : "memory");
+
+	return (sbiret_s){.error = a0, .value = a1};
+}
+
+void k_putchar(char ch) {
+	sbi_call(ch, 0, 0, 0, 0, 0, 0, 1);
+}
+
+void *k_memset(void *buf, char c, size_t n) {
+	u8 *p = (u8 *)buf;
+	while (n--) {
+		*p++ = c;
+	}
+
+	return buf;
+}
+
+/* Kernel main */
+void kernel_main(void) {
+	/* Usually it is not required */
+	k_memset(__bss, 0, __bss_end - __bss);
+
+	/* Start here */
+	r_printf("%s, %s\n", "Hello", "world!");
+	r_printf("3 + 4 = %d\n", 3 + 4);
+
+	for (;;) {
+		__asm__ __volatile__("wfi");
+	}
+}
+
+/* This is the entry section (boot) */
+__attribute__((section(".text.boot")))
+/* Do not add other stuff like return */
+__attribute__((naked)) void
+boot(void) {
+	/**
+	 * Put stack_top inside sp (stack pointer)
+	 * and jump to kernel_main
+	 */
+	__asm__ __volatile__("mv sp, %[stack_top]\n"
+						 "j kernel_main\n"
+						 :
+						 : [stack_top] "r"(__stack_top));
+}