Disk I/O

src/Makefile

@@ -1,5 +1,11 @@
 CC = clang
+OBJCOPY=llvm-objcopy
 CFLAGS = -std=c11 -O2 -g3 -Wall -Wextra --target=riscv32 -ffreestanding -nostdlib
 
-kernel:
-	$(CC) $(CFLAGS) -Wl,-Tkernel.ld -Wl,-Map=kernel.map -o kernel.elf kernel.c common.c
+kernel: shell
+	$(CC) $(CFLAGS) -Wl,-Tkernel.ld -Wl,-Map=kernel.map -o kernel.elf kernel.c common.c shell.bin.o
+
+shell:
+	$(CC) $(CFLAGS) -Wl,-Tuser.ld -Wl,-Map=shell.map -o shell.elf shell.c user.c common.c
+	$(OBJCOPY) --set-section-flags .bss=alloc,contents -O binary shell.elf shell.bin
+	$(OBJCOPY) -Ibinary -Oelf32-littleriscv shell.bin shell.bin.o

src/common.h

@@ -28,6 +28,10 @@ typedef uint32_t vaddr_t;
 
 #define PAGE_SIZE 4096
 
+#define USER_BASE 0x1000000
+
+#define SSTATUS_SPIE (1 << 5)
+
 void *memset(void *buf, char c, size_t n);
 void *memcpy(void *dst, const void *src, size_t n);
 

src/kernel.c

@@ -54,7 +54,7 @@ void map_page(uint32_t *table1, uint32_t vaddr, paddr_t paddr, uint32_t flags) {
 }
 
 // ===== Exception handler =====
-void kernel_entry(void) {
+__attribute__((naked)) __attribute__((aligned(4))) void kernel_entry(void) {
     __asm__ __volatile__("csrrw sp, sscratch, sp\n"
 
                          "addi sp, sp, -4 * 31\n"
@@ -89,9 +89,11 @@ void kernel_entry(void) {
                          "sw s10, 4 * 28(sp)\n"
                          "sw s11, 4 * 29(sp)\n"
 
+                         // Извлечение и сохранение sp в момент исключения.
                          "csrr a0, sscratch\n"
                          "sw a0,  4 * 30(sp)\n"
 
+                         // Сброс стека ядра.
                          "addi a0, sp, 4 * 31\n"
                          "csrw sscratch, a0\n"
 
@@ -182,7 +184,15 @@ __attribute__((naked)) void switch_context(uint32_t *prev_sp,
                          "ret\n");
 }
 
-struct process *create_process(uint32_t pc) {
+__attribute__((naked)) void user_entry(void) {
+    __asm__ __volatile__("csrw sepc, %[sepc]        \n"
+                         "csrw sstatus, %[sstatus]  \n"
+                         "sret                      \n"
+                         :
+                         : [sepc] "r"(USER_BASE), [sstatus] "r"(SSTATUS_SPIE));
+}
+
+struct process *create_process(const void *image, size_t image_size) {
     struct process *proc = NULL;
     int i;
     for (i = 0; i < PROCS_MAX; i++) {
@@ -196,25 +206,38 @@ struct process *create_process(uint32_t pc) {
         PANIC("no free process slots");
 
     uint32_t *sp = (uint32_t *)&proc->stack[sizeof(proc->stack)];
-    *--sp = 0;            // s11
-    *--sp = 0;            // s10
-    *--sp = 0;            // s9
-    *--sp = 0;            // s8
-    *--sp = 0;            // s7
-    *--sp = 0;            // s6
-    *--sp = 0;            // s5
-    *--sp = 0;            // s4
-    *--sp = 0;            // s3
-    *--sp = 0;            // s2
-    *--sp = 0;            // s1
-    *--sp = 0;            // s0
-    *--sp = (uint32_t)pc; // ra
+    *--sp = 0;                    // s11
+    *--sp = 0;                    // s10
+    *--sp = 0;                    // s9
+    *--sp = 0;                    // s8
+    *--sp = 0;                    // s7
+    *--sp = 0;                    // s6
+    *--sp = 0;                    // s5
+    *--sp = 0;                    // s4
+    *--sp = 0;                    // s3
+    *--sp = 0;                    // s2
+    *--sp = 0;                    // s1
+    *--sp = 0;                    // s0
+    *--sp = (uint32_t)user_entry; // ra
 
     uint32_t *page_table = (uint32_t *)alloc_pages(1);
+
     for (paddr_t paddr = (paddr_t)__kernel_base;
          paddr < (paddr_t)__free_ram_end; paddr += PAGE_SIZE)
         map_page(page_table, paddr, paddr, PAGE_R | PAGE_W | PAGE_X);
 
+    map_page(page_table, VIRTIO_BLK_PADDR, VIRTIO_BLK_PADDR, PAGE_R | PAGE_W);
+
+    for (uint32_t off = 0; off < image_size; off += PAGE_SIZE) {
+        paddr_t page = alloc_pages(1);
+
+        size_t remaining = image_size - off;
+        size_t copy_size = PAGE_SIZE <= remaining ? PAGE_SIZE : remaining;
+
+        memcpy((void *)page, image + off, copy_size);
+        map_page(page_table, USER_BASE + off, page,
+                 PAGE_U | PAGE_R | PAGE_W | PAGE_X);
+    }
     proc->pid = i + 1;
     proc->state = PROC_RUNNABLE;
     proc->sp = (uint32_t)sp;
@@ -248,35 +271,137 @@ void yield(void) {
     switch_context(&prev->sp, &next->sp);
 }
 
+// ===== Disk I/O =====
+uint32_t virtio_reg_read32(unsigned offset) {
+    return *((volatile uint32_t *)(VIRTIO_BLK_PADDR + offset));
+}
+
+uint64_t virtio_reg_read64(unsigned offset) {
+    return *((volatile uint64_t *)(VIRTIO_BLK_PADDR + offset));
+}
+
+void virtio_reg_write32(unsigned offset, uint32_t value) {
+    *((volatile uint32_t *)(VIRTIO_BLK_PADDR + offset)) = value;
+}
+
+void virtio_reg_fetch_and_or32(unsigned offset, uint32_t value) {
+    virtio_reg_write32(offset, virtio_reg_read32(offset) | value);
+}
+
+struct virtio_virtq *virtq_init(unsigned index) {
+    paddr_t virtq_paddr = alloc_pages(
+        align_up(sizeof(struct virtio_virtq), PAGE_SIZE) / PAGE_SIZE);
+    struct virtio_virtq *vq = (struct virtio_virtq *)virtq_paddr;
+    vq->queue_index = index;
+    vq->used_index = (volatile uint16_t *)&vq->used.index;
+    virtio_reg_write32(VIRTIO_REG_QUEUE_SEL, index);
+    virtio_reg_write32(VIRTIO_REG_QUEUE_NUM, VIRTQ_ENTRY_NUM);
+    virtio_reg_write32(VIRTIO_REG_QUEUE_ALIGN, 0);
+    virtio_reg_write32(VIRTIO_REG_QUEUE_PFN, virtq_paddr);
+    return vq;
+}
+
+void virtio_blk_init(void) {
+    if (virtio_reg_read32(VIRTIO_REG_MAGIC) != 0x74726976)
+        PANIC("virtio: invalid magic value");
+    if (virtio_reg_read32(VIRTIO_REG_VERSION) != 1)
+        PANIC("virtio: invalid version");
+    if (virtio_reg_read32(VIRTIO_REG_DEVICE_ID) != VIRTIO_DEVICE_BLK)
+        PANIC("virtio: invalid device id");
+
+    virtio_reg_write32(VIRTIO_REG_DEVICE_STATUS, 0);
+    virtio_reg_fetch_and_or32(VIRTIO_REG_DEVICE_STATUS, VIRTIO_STATUS_ACK);
+    virtio_reg_fetch_and_or32(VIRTIO_REG_DEVICE_STATUS, VIRTIO_STATUS_DRIVER);
+    virtio_reg_fetch_and_or32(VIRTIO_REG_DEVICE_STATUS, VIRTIO_STATUS_FEAT_OK);
+    blk_request_vq = virtq_init(0);
+    virtio_reg_write32(VIRTIO_REG_DEVICE_STATUS, VIRTIO_STATUS_DRIVER_OK);
+
+    blk_capacity =
+        virtio_reg_read64(VIRTIO_REG_DEVICE_CONFIG + 0) * SECTOR_SIZE;
+    printf("virtio-blk: capacity is %d bytes\n", blk_capacity);
+
+    blk_req_paddr =
+        alloc_pages(align_up(sizeof(*blk_req), PAGE_SIZE) / PAGE_SIZE);
+    blk_req = (struct virtio_blk_req *)blk_req_paddr;
+}
+
+void virtq_kick(struct virtio_virtq *vq, int desc_index) {
+    vq->avail.ring[vq->avail.index % VIRTQ_ENTRY_NUM] = desc_index;
+    vq->avail.index++;
+    __sync_synchronize();
+    virtio_reg_write32(VIRTIO_REG_QUEUE_NOTIFY, vq->queue_index);
+    vq->last_used_index++;
+}
+
+bool virtq_is_busy(struct virtio_virtq *vq) {
+    return vq->last_used_index != *vq->used_index;
+}
+
+void read_write_disk(void *buf, unsigned sector, int is_write) {
+    if (sector >= blk_capacity / SECTOR_SIZE) {
+        printf("virtio: tried to read/write sector=%d, but capacity is %d\n",
+               sector, blk_capacity / SECTOR_SIZE);
+        return;
+    }
+
+    blk_req->sector = sector;
+    blk_req->type = is_write ? VIRTIO_BLK_T_OUT : VIRTIO_BLK_T_IN;
+    if (is_write)
+        memcpy(blk_req->data, buf, SECTOR_SIZE);
+
+    struct virtio_virtq *vq = blk_request_vq;
+    vq->descs[0].addr = blk_req_paddr;
+    vq->descs[0].len = sizeof(uint32_t) * 2 + sizeof(uint64_t);
+    vq->descs[0].flags = VIRTQ_DESC_F_NEXT;
+    vq->descs[0].next = 1;
+
+    vq->descs[1].addr = blk_req_paddr + offsetof(struct virtio_blk_req, data);
+    vq->descs[1].len = SECTOR_SIZE;
+    vq->descs[1].flags =
+        VIRTQ_DESC_F_NEXT | (is_write ? 0 : VIRTQ_DESC_F_WRITE);
+    vq->descs[1].next = 2;
+
+    vq->descs[2].addr = blk_req_paddr + offsetof(struct virtio_blk_req, status);
+    vq->descs[2].len = sizeof(uint8_t);
+    vq->descs[2].flags = VIRTQ_DESC_F_WRITE;
+
+    virtq_kick(vq, 0);
+
+    while (virtq_is_busy(vq))
+        ;
+
+    if (blk_req->status != 0) {
+        printf("virtio: warn: failed to read/write sector=%d status=%d\n",
+               sector, blk_req->status);
+        return;
+    }
+
+    if (!is_write)
+        memcpy(buf, blk_req->data, SECTOR_SIZE);
+}
+
 // ===== ENTRY POINT =====
-struct process *proc_a;
-struct process *proc_b;
-
-void proc_a_entry(void) {
-    while (1) {
-        putchar('A');
-        yield();
-    }
-}
-
-void proc_b_entry(void) {
-    while (1) {
-        putchar('B');
-        yield();
-    }
-}
-
 void kernel_main(void) {
     memset(__bss, 0, (size_t)__bss_end - (size_t)__bss);
 
+    printf("\n\n");
+
     WRITE_CSR(stvec, (uint32_t)kernel_entry);
 
-    idle_proc = create_process((uint32_t)NULL);
+    virtio_blk_init();
+
+    char buf[SECTOR_SIZE];
+    read_write_disk(buf, 0, false);
+    printf("first sector: %s\n", buf);
+
+    strcpy(buf, "hello from kernel!!!\n");
+    read_write_disk(buf, 0, true);
+
+    idle_proc = create_process(NULL, 0);
     idle_proc->pid = -1;
     current_proc = idle_proc;
 
-    proc_a = create_process((uint32_t)proc_a_entry);
-    proc_b = create_process((uint32_t)proc_b_entry);
+    create_process(_binary_shell_bin_start, (size_t)_binary_shell_bin_size);
 
     yield();
     PANIC("switched to idle process");

src/kernel.h

@@ -7,6 +7,7 @@ extern char __bss[], __bss_end[];
 extern char __stack_top[];
 extern char __free_ram[], __free_ram_end[];
 extern char __kernel_base[];
+extern char _binary_shell_bin_start[], _binary_shell_bin_size[];
 
 // ===== SBI data ======
 struct sbiret {
@@ -74,6 +75,79 @@ struct process *idle_proc;
 #define PAGE_X (1 << 3)
 #define PAGE_U (1 << 4)
 
+// ===== Disk I/O =====
+#define SECTOR_SIZE 512
+#define VIRTQ_ENTRY_NUM 16
+#define VIRTIO_DEVICE_BLK 2
+#define VIRTIO_BLK_PADDR 0x10001000
+#define VIRTIO_REG_MAGIC 0x00
+#define VIRTIO_REG_VERSION 0x04
+#define VIRTIO_REG_DEVICE_ID 0x08
+#define VIRTIO_REG_QUEUE_SEL 0x30
+#define VIRTIO_REG_QUEUE_NUM_MAX 0x34
+#define VIRTIO_REG_QUEUE_NUM 0x38
+#define VIRTIO_REG_QUEUE_ALIGN 0x3c
+#define VIRTIO_REG_QUEUE_PFN 0x40
+#define VIRTIO_REG_QUEUE_READY 0x44
+#define VIRTIO_REG_QUEUE_NOTIFY 0x50
+#define VIRTIO_REG_DEVICE_STATUS 0x70
+#define VIRTIO_REG_DEVICE_CONFIG 0x100
+#define VIRTIO_STATUS_ACK 1
+#define VIRTIO_STATUS_DRIVER 2
+#define VIRTIO_STATUS_DRIVER_OK 4
+#define VIRTIO_STATUS_FEAT_OK 8
+#define VIRTQ_DESC_F_NEXT 1
+#define VIRTQ_DESC_F_WRITE 2
+#define VIRTQ_AVAIL_F_NO_INTERRUPT 1
+#define VIRTIO_BLK_T_IN 0
+#define VIRTIO_BLK_T_OUT 1
+
+struct virtq_desc {
+    uint64_t addr;
+    uint32_t len;
+    uint16_t flags;
+    uint16_t next;
+} __attribute__((packed));
+
+struct virtq_avail {
+    uint16_t flags;
+    uint16_t index;
+    uint16_t ring[VIRTQ_ENTRY_NUM];
+} __attribute__((packed));
+
+struct virtq_used_elem {
+    uint32_t id;
+    uint32_t len;
+} __attribute__((packed));
+
+struct virtq_used {
+    uint16_t flags;
+    uint16_t index;
+    struct virtq_used_elem ring[VIRTQ_ENTRY_NUM];
+} __attribute__((packed));
+
+struct virtio_virtq {
+    struct virtq_desc descs[VIRTQ_ENTRY_NUM];
+    struct virtq_avail avail;
+    struct virtq_used used __attribute__((aligned(PAGE_SIZE)));
+    int queue_index;
+    volatile uint16_t *used_index;
+    uint16_t last_used_index;
+} __attribute__((packed));
+
+struct virtio_blk_req {
+    uint32_t type;
+    uint32_t reserved;
+    uint64_t sector;
+    uint8_t data[512];
+    uint8_t status;
+} __attribute__((packed));
+
+struct virtio_virtq *blk_request_vq;
+struct virtio_blk_req *blk_req;
+paddr_t blk_req_paddr;
+unsigned blk_capacity;
+
 // ===== Macros =====
 #define READ_CSR(reg)                                                          \
     ({                                                                         \

src/run.bat

@@ -1,4 +1,6 @@
 @echo off
 make kernel
 cd /d "C:\Program Files\qemu"
-qemu-system-riscv32.exe -machine virt -bios default -nographic -serial mon:stdio --no-reboot -kernel %~dp0kernel.elf
+qemu-system-riscv32.exe -machine virt -bios default -nographic -serial mon:stdio --no-reboot -drive id=drive0,file=lorem.txt,format=raw,if=none -device virtio-blk-device,drive=drive0,bus=virtio-mmio-bus.0 -kernel %~dp0kernel.elf
+
+

src/run.sh

@@ -1,4 +1,4 @@
 #!/bin/bash
 set -xue
 
-make kernel && qemu-system-riscv32 -machine virt -bios default -nographic -serial mon:stdio --no-reboot -kernel kernel.elf
+make kernel && qemu-system-riscv32 -machine virt -bios default -nographic -serial mon:stdio --no-reboot -drive id=drive0,file=lorem.txt,format=raw,if=none -device virtio-blk-device,drive=drive0,bus=virtio-mmio-bus.0 -kernel kernel.elf

src/shell.c

@@ -0,0 +1,6 @@
+#include "user.h"
+
+void main(void) {
+    for (;;)
+        ;
+}

src/user.c

@@ -0,0 +1,18 @@
+#include "user.h"
+
+extern char __stack_top[];
+
+__attribute__((noreturn)) void exit(void) {
+    for (;;)
+        ;
+}
+
+void putchar(char c) { /* Доделать*/ }
+
+__attribute__((section(".text.start"))) __attribute__((naked)) void
+start(void) {
+    __asm__ __volatile__(
+        "mv sp, %[stack_top] \n"
+        "call main           \n"
+        "call exit           \n" ::[stack_top] "r"(__stack_top));
+}

src/user.h

@@ -0,0 +1,6 @@
+#pragma once
+
+#include "common.h"
+
+__attribute__((noreturn)) void exit(void);
+void putchar(char ch);

src/user.ld

@@ -0,0 +1,28 @@
+ENTRY(start)
+
+SECTIONS {
+    . = 0x1000000;
+
+    .text :{
+        KEEP(*(.text.start));
+        *(.text .text.*);
+    }
+
+    .rodata : ALIGN(4) {
+        *(.rodata .rodata.*);
+    }
+
+    .data : ALIGN(4) {
+        *(.data .data.*);
+    }
+
+    .bss : ALIGN(4) {
+        *(.bss .bss.* .sbss .sbss.*);
+
+        . = ALIGN(16);
+        . += 64 * 1024; /* 64KB */
+        __stack_top = .;
+
+       ASSERT(. < 0x1800000, "too large executable");
+    }
+}