如何找到一个ELF文件的节头字符串表的偏移量? [英] How to find the offset of the section header string table of an elf file?
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问题描述
我必须写,打印一个ELF文件的C程序。我无法搞清楚节头字符串表。
I have to write a C program that prints an ELF file. I'm having trouble figuring out where the section header string table is.
让我们说我有这给了我下面的输出文件:
Let's say I have a file that gave me the following output with:
readelf -h
readelf -h
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: 17636 (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: 23
Section header string table index: 20
和
readelf -S
readelf -S:
There are 23 section headers, starting at offset 0x44e4:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
[ 0] NULL 00000000 000000 000000 00 0 0 0
[ 1] .text PROGBITS 00000000 000034 000028 00 AX 0 0 4
[ 2] .rel.text REL 00000000 0049d0 000018 08 21 1 4
[ 3] .data PROGBITS 00000000 00005c 000000 00 WA 0 0 4
[ 4] .bss NOBITS 00000000 00005c 000000 00 WA 0 0 4
[ 5] .rodata PROGBITS 00000000 00005c 00000a 00 A 0 0 1
[ 6] .debug_info PROGBITS 00000000 000066 00008f 00 0 0 1
[ 7] .rel.debug_info REL 00000000 0049e8 0000b0 08 21 6 4
[ 8] .debug_abbrev PROGBITS 00000000 0000f5 000041 00 0 0 1
[ 9] .debug_loc PROGBITS 00000000 000136 000038 00 0 0 1
[10] .debug_aranges PROGBITS 00000000 00016e 000020 00 0 0 1
[11] .rel.debug_arange REL 00000000 004a98 000010 08 21 10 4
[12] .debug_line PROGBITS 00000000 00018e 0001b3 00 0 0 1
[13] .rel.debug_line REL 00000000 004aa8 000008 08 21 12 4
[14] .debug_macinfo PROGBITS 00000000 000341 003fb9 00 0 0 1
[15] .debug_str PROGBITS 00000000 0042fa 0000bf 01 MS 0 0 1
[16] .comment PROGBITS 00000000 0043b9 00002b 01 MS 0 0 1
[17] .note.GNU-stack PROGBITS 00000000 0043e4 000000 00 0 0 1
[18] .eh_frame PROGBITS 00000000 0043e4 000038 00 A 0 0 4
[19] .rel.eh_frame REL 00000000 004ab0 000008 08 21 18 4
[20] .shstrtab STRTAB 00000000 00441c 0000c5 00 0 0 1
[21] .symtab SYMTAB 00000000 00487c 000130 10 22 16 4
[22] .strtab STRTAB 00000000 0049ac 000021 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)
我
如何将能够计算出节头字符串表的位置?
How would I be able to calculate the location of the section header string table?
推荐答案
这是我做的:
#pragma pack(push,1)
typedef struct
{
uint8 e_ident[16];
uint16 e_type;
uint16 e_machine;
uint32 e_version;
uint32 e_entry;
uint32 e_phoff;
uint32 e_shoff;
uint32 e_flags;
uint16 e_ehsize;
uint16 e_phentsize;
uint16 e_phnum;
uint16 e_shentsize;
uint16 e_shnum;
uint16 e_shstrndx;
} Elf32Hdr;
typedef struct
{
uint32 sh_name;
uint32 sh_type;
uint32 sh_flags;
uint32 sh_addr;
uint32 sh_offset;
uint32 sh_size;
uint32 sh_link;
uint32 sh_info;
uint32 sh_addralign;
uint32 sh_entsize;
} Elf32SectHdr;
#pragma pack(pop)
{
FILE* ElfFile = NULL;
char* SectNames = NULL;
Elf32Hdr elfHdr;
Elf32SectHdr sectHdr;
uint idx;
// ...
// read ELF header
fread(&elfHdr, 1, sizeof elfHdr, ElfFile);
// read section name string table
// first, read its header
fseek(ElfFile, elfHdr.e_shoff + elfHdr.e_shstrndx * sizeof sectHdr, SEEK_SET);
fread(§Hdr, 1, sizeof sectHdr, ElfFile);
// next, read the section, string data
SectNames = malloc(sectHdr.sh_size);
fseek(ElfFile, sectHdr.sh_offset, SEEK_SET);
fread(SectNames, 1, sectHdr.sh_size, ElfFile);
// read all section headers
for (idx = 0; idx < elfHdr.e_shnum; idx++)
{
const char* name = "";
fseek(ElfFile, elfHdr.e_shoff + idx * sizeof sectHdr, SEEK_SET);
fread(§Hdr, 1, sizeof sectHdr, ElfFile);
// print section name
if (sectHdr.sh_name);
name = SectNames + sectHdr.sh_name;
printf("%2u %s\n", idx, name);
}
// ...
}
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