From bbcf34f1f65a6558dd5c5150fdf28153d5958474 Mon Sep 17 00:00:00 2001
From: Alex Kotov <kotovalexarian@gmail.com>
Date: Sun, 16 Jan 2022 20:14:56 +0500
Subject: [PATCH] Write MBR

---
 .gitignore            |  1 +
 configure.ac          |  2 +-
 src/main.c            | 61 +++++++++++++++++++++++++++++++++++++++++--
 src/x86_boot_sector.S |  3 ---
 4 files changed, 61 insertions(+), 6 deletions(-)

diff --git a/.gitignore b/.gitignore
index 829b309..b2b801b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,6 +5,7 @@
 *.a
 *.bin
 *.c.d
+*.img
 *.o
 
 .deps/
diff --git a/configure.ac b/configure.ac
index 0f6e626..1c94a14 100644
--- a/configure.ac
+++ b/configure.ac
@@ -27,6 +27,6 @@ AC_PROG_CC_C99
 AC_PROG_RANLIB
 AC_C_INLINE
 AC_CHECK_HEADER_STDBOOL
-AC_CHECK_HEADERS([stdarg.h stddef.h stdint.h stdio.h])
+AC_CHECK_HEADERS([stdarg.h stddef.h stdint.h stdio.h string.h])
 
 AC_OUTPUT
diff --git a/src/main.c b/src/main.c
index cf08d55..923535e 100644
--- a/src/main.c
+++ b/src/main.c
@@ -18,8 +18,10 @@
 
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h>
 
 #define MBR_SIZE 512
+#define MBR_BOOTSTRAP_SIZE (MBR_SIZE - sizeof(struct MbrInfo))
 #define MBR_ENTRIES 4
 #define MBR_MAGIC 0xAA55
 
@@ -42,13 +44,68 @@ struct MbrInfo {
 __attribute__((packed));
 
 struct Mbr {
-    uint8_t bootstrap[MBR_SIZE - sizeof(struct MbrInfo)];
+    uint8_t bootstrap[MBR_BOOTSTRAP_SIZE];
     struct MbrInfo info;
 }
 __attribute__((packed));
 
 int main()
 {
-    printf("Hello, World!\n");
+    struct Mbr mbr;
+
+    {
+        memset(&mbr, 0, sizeof(mbr));
+
+        mbr.info.magic = MBR_MAGIC;
+        mbr.info.disk_id = 0;
+        mbr.info.reserved = 0;
+    }
+
+    {
+        FILE *fd = fopen("src/x86_boot_sector.bin", "r");
+        if (fd == NULL) {
+            fprintf(stderr, "Can't open bootstrap file\n");
+            return 1;
+        }
+
+        const size_t size = fread(&mbr.bootstrap, 1, MBR_BOOTSTRAP_SIZE, fd);
+        if (size == 0) {
+            fprintf(stderr, "Empty bootstrap file\n");
+            return 1;
+        }
+        if (!feof(fd)) {
+            fprintf(stderr, "Too long bootstrap file\n");
+            return 1;
+        }
+
+        fclose(fd);
+    }
+
+    uint8_t *mbr_ptr = (uint8_t*)&mbr;
+
+    for (size_t i = 0; i < 512 / 16; ++i) {
+        printf("%02x", mbr_ptr[i * 16]);
+        for (size_t j = 1; j < 16; ++j) {
+            printf(" %02x", mbr_ptr[i * 16 + j]);
+        }
+        printf("\n");
+    }
+
+    {
+        FILE *fd = fopen("disk.img", "wb");
+        if (fd == NULL) {
+            fprintf(stderr, "Can't open image file\n");
+            return 1;
+        }
+
+        const size_t size = fwrite(mbr_ptr, 1, sizeof(mbr), fd);
+        if (size != sizeof(mbr)) {
+            fprintf(stderr, "Can't write image file\n");
+            return 1;
+        }
+
+        fclose(fd);
+    }
+
     return 0;
 }
diff --git a/src/x86_boot_sector.S b/src/x86_boot_sector.S
index 58e1c20..392ae60 100644
--- a/src/x86_boot_sector.S
+++ b/src/x86_boot_sector.S
@@ -37,6 +37,3 @@ _start:
     int $0x10
 _loop:
     jmp _loop
-_end:
-.fill 510 - (_end - _start), 1, 0
-.byte 0x55, 0xAA