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完成对 ELF 格式文件头(ELF Header)的读取，实现 readelf -a 的功能。
$ readelf -a max.o ELF Header: Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 Class: ELF32 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: REL (Relocatable file) Machine: Intel 80386 Version: 0x1 Entry point address: 0x0 Start of program headers: 0 (bytes into file) Start of section headers: 200 (bytes into file) Flags: 0x0 Size of this header: 52 (bytes) Size of program headers: 0 (bytes) Number of program headers: 0 Size of section headers: 40 (bytes) Number of section headers: 8 Section header string table index: 5 -
在完成上述功能的基础上，能够区分 .o .so .elf 这3种文件属性，实现 file 命令的部分功能。
$ gcc -c hello.c -o hello.o $ file hello.o hello.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped $ gcc hello.c -o a.out $ file a.out a.out: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1], not stripped
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常用 API
printf(); 格式化输出数据 scanf(); 格式输入函数 sprintf(); 格式化字符串复制 sscanf(); 格式化字符串输入 vfprintf(); 格式化输出数据至文件 vprintf(); 格式化输出数据 vsprintf(); 格式化字符串复制 getc(); 由文件中读取一个字符 putc(); 将一指定字符写入文件中 getchar(); 由标准输入设备内读进一字符 putchar(); 将指定的字符写到标准输出设备 gets(); 由标准输入设备内读进一字符串 puts(); 送一字符串到流stdout中 ungetc(); 将指定字符写回文件流中 perror(); 打印出错误原因信息字符串
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typedef struct { Elf32_Char e_ident[EI_NIDENT]; Elf32_Half e_type; Elf32_Half e_machine; Elf32_Word e_version; Elf32_Addr e_entry; /** Entry point */ Elf32_Off e_phoff; Elf32_Off e_shoff; Elf32_Word e_flags; Elf32_Half e_ehsize; Elf32_Half e_phentsize; Elf32_Half e_phnum; Elf32_Half e_shentsize; Elf32_Half e_shnum; Elf32_Half e_shstrndx; } Elf32_Ehdr;
struct type_string
{
int type;
char *string;
} s[] =
{
{ 0, "Unknow" },
{ 2, "EXEC" },
{ 1, "REL" },
{ -1, "Other Format" },
};
// ELF Header size
#define HSIZE (int)sizeof(Elf32_Ehdr)
char buf[HSIZE];
int n;
n = fread(buf, HSIZE, 1, fp);
Elf32_Ehdr * p;
p = (Elf32_Ehdr *)buf;
printf("type = %d\n", p->e_type);
printf("Type: %s\n", s[get_type_index(p->e_type)].string);