readelf
Used to display information about elf format files
Supplementary instructions
readelf command is used to display information about one or more target files in elf format. You can control what information is displayed through its options. The elf-file(s) here represents the files being checked. It can support 32-bit and 64-bit elf format files, and also supports documents containing elf files (this generally refers to "static library" files such as lib*.a generated after using the ar command to package some elf files) .
This program provides similar functions to objdump, but the information it displays is more specific, and it does not rely on the BFD library (the BFD library is a GNU project, and its goal is to process different target files through a unified interface) , so even if there are any bugs in the BFD library, it will not affect the readelf program.
When running readelf, in addition to -v and -H, one of the other options must be specified.
ELF file type
Types of ELF files:
ELF file function:
ELF files participate in program connection (creating a program) and program execution (running a program), so elf format files can be viewed from different perspectives:
Overall composition of ELF file:
The elf file header describes the overall information of the elf file. Including: system related, type related, loading related, link related.
Options
-a
--all displays all information, equivalent to -h -l -S -s -r -d -V -A -I.
-h
--file-header displays the file header information at the beginning of the elf file.
-l
--program-headers
--segments Display program header (segment header) information (if any).
-S
--section-headers
--sections Display section header information (if any).
-g
--section-groups Display section group information (if any).
-t
--section-details Show section details (-S).
-s
--syms
--symbols Display the entries in the symbol table section (if any).
-e
--headers displays all header information, equivalent to: -h -l -S
-n
--notes displays information about note segments (kernel comments).
-r
--relocs Display information about relocatable segments.
-u
--unwind displays unwind segment information. Currently only the unwind segment information of IA64 ELF is supported.
-d
--dynamic displays information about dynamic segments.
-V
--version-info Display version segment information.
-A
--arch-specific displays CPU architecture information.
-D
--use-dynamic Use the symbol table in the dynamic segment to display symbols instead of using the symbol segment.
-x <number or name>
--hex-dump=<number or name> Display the contents of the specified segment in hexadecimal format. The number specifies the index of the segment in the segment table, or the string specifies the segment name in the file.
-w[liaprmfFsoR] or
--debug-dump[=line,=info,=abbrev,=pubnames,=aranges,=macro,=frames,=frames-interp,=str,=loc,=Ranges] Display the content specified in the debug section.
-I
--histogram When displaying symbols, display a histogram of the bucket list length.
-v
--version displays readelf version information.
-H
--help displays the command line options supported by readelf.
-W
--wide wide line output.
@file You can collect options into a file and then load it using this @file option.Example
First give the following example:
**1. For elf format files in the form of executable files: **
root@localhost [test]$ cat main.cpp
#include <iostream>
using std::cout;
using std::endl;
void my_print();
int main(int argc, char *argv[])
{
my_print();
cout<<"hello!"<<endl;
return 0;
}
void my_print()
{
cout<<"print!"<<endl;
}[root@localhost test]$ g++ main.cpp -o main
[root@localhost test]$ g++ -g main.cpp -o main.debug[root@localhost test]$ ls -l
Total 64
-rwxr-xr-x 1 quietheart quietheart 6700 07-07 18:04 main
-rw-r--r-- 1 quietheart quietheart 201 07-07 18:02 main.cpp
-rwxr-xr-x 1 quietheart quietheart 38932 07-07 18:04 main.debugHere, main.debug is an executable file with debugging information, and main is a general executable file.
**2. For elf format files in the form of library files: **
//myfile.h
#ifndef __MYFILE_H
#define __MYFILE_H
void printInfo();
#endif
//myfile.cpp
#include "myfile.h"
#include <iostream>
using std::cout;
using std::endl;
void printInfo()
{
cout<<"hello"<<endl;
}[root@localhost test]$ g++ -c myfile.cpp
[root@localhost test]$ g++ -shared -fPCI -o libmy.so myfile.o
[root@localhost test]$ ar -r libmy.a myfile.o
ar: creating libmy.a[root@localhost test]$ ls -l
Total 44
-rw-r--r-- 1 quietheart quietheart 2154 07-08 16:14 libmy.a
-rwxr-xr-x 1 quietheart quietheart 5707 07-08 16:08 libmy.so
-rwxr-xr-x 1 quietheart quietheart 117 07-08 16:06 myfile.cpp
-rwxr-xr-x 1 quietheart quietheart 63 07-08 16:08 myfile.h
-rw-r--r-- 1 quietheart quietheart 2004 07-08 16:08 myfile.o
libmy.a libmy.so myfile.cpp myfile.h myfile.oHere, the target file myfile.o, the shared library file libmy.so, and the static library file libmy.a are generated respectively.
Based on the above executable files and libraries, here are some commonly used commands.
Read elf file header information in the form of executable file:
[root@localhost test]$ readelf -h main
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: exec (Executable file)
Machine: Intel 80386
Version: 0x1
Entry point address: 0x8048580
Start of program headers: 52 (bytes into file)
Start of section headers: 3232 (bytes into file)
Flags: 0x0
Size of this header: 52 (bytes)
Size of program headers: 32 (bytes)
Number of program headers: 8
Size of section headers: 40 (bytes)
Number of section headers: 29
Section header string table index: 26Here, you can see the elf file of the executable file, whose type is EXEC (executable file). In addition, the contents of "main.debug" containing debugging information and "main" without debugging information are the same except for some size information. And it can be seen that the architecture of the file is Intel 80386.
Read the elf file header information in the form of the target file:
[root@localhost test]$readelf -h myfile.o
ELF Header:
Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
Class: ELF32
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: REL (Relocatable file)
Machine: Intel 80386
Version: 0x1
Entry point address: 0x0
Start of program headers: 0 (bytes into file)
Start of section headers: 516 (bytes into file)
Flags: 0x0
Size of this header: 52 (bytes)
Size of program headers: 0 (bytes)
Number of program headers: 0
Size of section headers: 40 (bytes)
Number of section headers: 15
Section header string table index: 12Here, you can see the elf file of the target file, whose type is REL (relocatable file).
Read the elf file header information in the form of a static library file:
[root@localhost test]$ readelf -h libmy.a
File: libmy.a(myfile.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: 516 (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: 15
Section header string table index: 12Here, you can see the elf file of the static library file, whose type is REL (relocatable file).
Read elf file header information in the form of dynamic library file:
[root@localhost test]$ readelf -h libmy.so
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: DYN (Shared object file)
Machine: Intel 80386
Version: 0x1
Entry point address: 0x550
Start of program headers: 52 (bytes into file)
Start of section headers: 2768 (bytes into file)
Flags: 0x0
Size of this header: 52 (bytes)
Size of program headers: 32 (bytes)
Number of program headers: 5
Size of section headers: 40 (bytes)
Number of section headers: 27
Section header string table index: 24Here, you can see the elf file of the dynamic library file, whose type is DYN (shared object file).
View executable elf file program header table information:
[root@localhost test]$ readelf -l main
Elf file type is EXEC (Executable file)
Entry point 0x8048580
There are 8 program headers, starting at offset 52
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
PHDR 0x000034 0x08048034 0x08048034 0x00100 0x00100 R E 0x4
INTERP 0x000134 0x08048134 0x08048134 0x00013 0x00013 R 0x1
Requesting program interpreter: /lib/[ld-linux.so.2]
LOAD 0x000000 0x08048000 0x08048000 0x00970 0x00970 R E 0x1000
LOAD 0x000970 0x08049970 0x08049970 0x00130 0x001c8 RW 0x1000
DYNAMIC 0x000988 0x08049988 0x08049988 0x000e0 0x000e0 RW 0x4
NOTE 0x000148 0x08048148 0x08048148 0x00020 0x00020 R 0x4
GNU_EH_FRAME 0x000820 0x08048820 0x08048820 0x00044 0x00044 R 0x4
GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0x4
Section to Segment mapping:
Segment Sections...
00
01 .interp
02 .interp .note.ABI-tag .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rel.dyn .rel.plt .init .plt .text .fini .rodata .eh_frame_hdr .eh_frame
03 .ctors .dtors .jcr .dynamic .got .got.plt .data .bss
04 .dynamic
05 .note.ABI-tag
06 .eh_frame_hdr
07Here, the contents of "main.debug" containing debugging information and "main" without debugging information are the same.
**View the elf file program header table information of the target file: **
[root@localhost test]$ readelf -l myfile.o
There are no program headers in this file.It can be seen here that a relocatable target file does not have a program header table.
View the program header table information of the elf file of the static library file:
[root@localhost test]$ readelf -l libmy.a
File: libmy.a(myfile.o)
There are no program headers in this file.It can be seen here that the relocatable static library file does not have a program header table.
View the elf file program header table information of the dynamic library file:
[root@localhost test]$ readelf -l libmy.so
Elf file type is DYN (Shared object file)
Entry point 0x550
There are 5 program headers, starting at offset 52
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
LOAD 0x000000 0x00000000 0x00000000 0x007f4 0x007f4 R E 0x1000
LOAD 0x0007f4 0x000017f4 0x000017f4 0x0011c 0x00128 RW 0x1000
DYNAMIC 0x000810 0x00001810 0x00001810 0x000e0 0x000e0 RW 0x4
GNU_EH_FRAME 0x000738 0x00000738 0x00000738 0x0002c 0x0002c R 0x4
GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0x4
Section to Segment mapping:
Segment Sections...
00 .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rel.dyn .rel.plt .init .plt .text .fini .rodata .eh_frame_hdr .eh_frame
01 .ctors .dtors .jcr .data.rel.ro .dynamic .got .got.plt .bss
02 .dynamic
03 .eh_frame_hdr
04 It can be seen here that as a dynamic library of shared object files, its program header table.
View the section information of an executable elf file:
[root@localhost test]$ readelf -S main
There are 29 section headers, starting at offset 0xca0:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
[ 0] NULL 00000000 000000 000000 00 0 0 0
[ 1] .interp PROGBITS 08048134 000134 000013 00 A 0 0 1
[ 2] .note.ABI-tag NOTE 08048148 000148 000020 00 A 0 0 4
[ 3] .gnu.hash GNU_HASH 08048168 000168 000030 04 A 4 0 4
[ 4] .dynsym DYNSYM 08048198 000198 0000d0 10 A 5 1 4
[ 5] .dynstr STRTAB 08048268 000268 000183 00 A 0 0 1
[ 6] .gnu.version VERSYM 080483ec 0003ec 00001a 02 A 4 0 2
[ 7] .gnu.version_r VERNEED 08048408 000408 000060 00 A 5 2 4
[ 8] .rel.dyn REL 08048468 000468 000010 08 A 4 0 4
[ 9] .rel.plt REL 08048478 000478 000048 08 A 4 11 4
[10] .init PROGBITS 080484c0 0004c0 000017 00 AX 0 0 4
[11] .plt PROGBITS 080484d8 0004d8 0000a0 04 AX 0 0 4
[12] .text PROGBITS 08048580 000580 000268 00 AX 0 0 16
[13] .fini PROGBITS 080487e8 0007e8 00001c 00 AX 0 0 4
[14] .rodata PROGBITS 08048804 000804 00001a 00 A 0 0 4
[15] .eh_frame_hdr PROGBITS 08048820 000820 000044 00 A 0 0 4
[16] .eh_frame PROGBITS 08048864 000864 00010c 00 A 0 0 4
[17] .ctors PROGBITS 08049970 000970 00000c 00 WA 0 0 4
[18] .dtors PROGBITS 0804997c 00097c 000008 00 WA 0 0 4
[19] .jcr PROGBITS 08049984 000984 000004 00 WA 0 0 4
[20] .dynamic DYNAMIC 08049988 000988 0000e0 08 WA 5 0 4
[21] .got PROGBITS 08049a68 000a68 000004 04 WA 0 0 4
[22] .got.plt PROGBITS 08049a6c 000a6c 000030 04 WA 0 0 4
[23] .data PROGBITS 08049a9c 000a9c 000004 00 WA 0 0 4
[24] .bss NOBITS 08049aa0 000aa0 000098 00 WA 0 0 8
[25] .comment PROGBITS 00000000 000aa0 000114 00 0 0 1
[26] .shstrtab STRTAB 00000000 000bb4 0000e9 00 0 0 1
[27] .symtab SYMTAB 00000000 001128 000510 10 28 53 4
[28] .strtab STRTAB 00000000 001638 0003f4 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific) Here, main is the executable file without debugging information.
View the section information of an executable elf file that contains debugging information:
[root@localhost test]$ readelf -S main.debug
There are 37 section headers, starting at offset 0x88c8:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
[ 0] NULL 00000000 000000 000000 00 0 0 0
[ 1] .interp PROGBITS 08048134 000134 000013 00 A 0 0 1
[ 2] .note.ABI-tag NOTE 08048148 000148 000020 00 A 0 0 4
[ 3] .gnu.hash GNU_HASH 08048168 000168 000030 04 A 4 0 4
[ 4] .dynsym DYNSYM 08048198 000198 0000d0 10 A 5 1 4
[ 5] .dynstr STRTAB 08048268 000268 000183 00 A 0 0 1
[ 6] .gnu.version VERSYM 080483ec 0003ec 00001a 02 A 4 0 2
[ 7] .gnu.version_r VERNEED 08048408 000408 000060 00 A 5 2 4
[ 8] .rel.dyn REL 08048468 000468 000010 08 A 4 0 4
[ 9] .rel.plt REL 08048478 000478 000048 08 A 4 11 4
[10] .init PROGBITS 080484c0 0004c0 000017 00 AX 0 0 4
[11] .plt PROGBITS 080484d8 0004d8 0000a0 04 AX 0 0 4
[12] .text PROGBITS 08048580 000580 000268 00 AX 0 0 16
[13] .fini PROGBITS 080487e8 0007e8 00001c 00 AX 0 0 4
[14] .rodata PROGBITS 08048804 000804 00001a 00 A 0 0 4
[15] .eh_frame_hdr PROGBITS 08048820 000820 000044 00 A 0 0 4
[16] .eh_frame PROGBITS 08048864 000864 00010c 00 A 0 0 4
[17] .ctors PROGBITS 08049970 000970 00000c 00 WA 0 0 4
[18] .dtors PROGBITS 0804997c 00097c 000008 00 WA 0 0 4
[19] .jcr PROGBITS 08049984 000984 000004 00 WA 0 0 4
[20] .dynamic DYNAMIC 08049988 000988 0000e0 08 WA 5 0 4
[21] .got PROGBITS 08049a68 000a68 000004 04 WA 0 0 4
[22] .got.plt PROGBITS 08049a6c 000a6c 000030 04 WA 0 0 4
[23] .data PROGBITS 08049a9c 000a9c 000004 00 WA 0 0 4
[24] .bss NOBITS 08049aa0 000aa0 000098 00 WA 0 0 8
[25] .comment PROGBITS 00000000 000aa0 000114 00 0 0 1
[26] .debug_aranges PROGBITS 00000000 000bb4 000020 00 0 0 1
[27] .debug_pubnames PROGBITS 00000000 000bd4 000028 00 0 0 1
[28] .debug_info PROGBITS 00000000 000bfc 0067aa 00 0 0 1
[29] .debug_abbrev PROGBITS 00000000 0073a6 000726 00 0 0 1
[30] .debug_line PROGBITS 00000000 007acc 0003e1 00 0 0 1
[31] .debug_frame PROGBITS 00000000 007eb0 00009c 00 0 0 4
[32] .debug_str PROGBITS 00000000 007f4c 000735 00 0 0 1
[33] .debug_loc PROGBITS 00000000 008681 0000f3 00 0 0 1
[34] .shstrtab STRTAB 00000000 008774 000151 00 0 0 1
[35] .symtab SYMTAB 00000000 008e90 000590 10 36 61 4
[36] .strtab STRTAB 00000000 009420 0003f4 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific) It can be seen that compared with the non-debug version of the executable file, there is more ".debug*" section information.
View the section information of the elf file of a target file:
[root@localhost test]$ readelf -S myfile.o
There are 15 section headers, starting at offset 0x204:
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 00009e 00 AX 0 0 4
[ 2] .rel.text REL 00000000 000744 000060 08 13 1 4
[ 3] .data PROGBITS 00000000 0000d4 000000 00 WA 0 0 4
[ 4] .bss NOBITS 00000000 0000d4 000001 00 WA 0 0 4
[ 5] .ctors PROGBITS 00000000 0000d4 000004 00 WA 0 0 4
[ 6] .rel.ctors REL 00000000 0007a4 000008 08 13 5 4
[ 7] .rodata PROGBITS 00000000 0000d8 000006 00 A 0 0 1
[ 8] .eh_frame PROGBITS 00000000 0000e0 00008c 00 A 0 0 4
[ 9] .rel.eh_frame REL 00000000 0007ac 000028 08 13 8 4
[10] .comment PROGBITS 00000000 00016c 00002e 00 0 0 1
[11] .note.GNU-stack PROGBITS 00000000 00019a 000000 00 0 0 1
[12] .shstrtab STRTAB 00000000 00019a 00006a 00 0 0 1
[13] .symtab SYMTAB 00000000 00045c 000180 10 14 14 4
[14] .strtab STRTAB 00000000 0005dc 000166 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)
```shell
**查看一个静态库文件的elf文件的节信息：**
```shell
[root@localhost test]$ readelf -S libmy.a
File: libmy.a(myfile.o)
There are 15 section headers, starting at offset 0x204:
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 00009e 00 AX 0 0 4
[ 2] .rel.text REL 00000000 000744 000060 08 13 1 4
[ 3] .data PROGBITS 00000000 0000d4 000000 00 WA 0 0 4
[ 4] .bss NOBITS 00000000 0000d4 000001 00 WA 0 0 4
[ 5] .ctors PROGBITS 00000000 0000d4 000004 00 WA 0 0 4
[ 6] .rel.ctors REL 00000000 0007a4 000008 08 13 5 4
[ 7] .rodata PROGBITS 00000000 0000d8 000006 00 A 0 0 1
[ 8] .eh_frame PROGBITS 00000000 0000e0 00008c 00 A 0 0 4
[ 9] .rel.eh_frame REL 00000000 0007ac 000028 08 13 8 4
[10] .comment PROGBITS 00000000 00016c 00002e 00 0 0 1
[11] .note.GNU-stack PROGBITS 00000000 00019a 000000 00 0 0 1
[12] .shstrtab STRTAB 00000000 00019a 00006a 00 0 0 1
[13] .symtab SYMTAB 00000000 00045c 000180 10 14 14 4
[14] .strtab STRTAB 00000000 0005dc 000166 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific) View the section information of the elf file of a dynamic library file:
[root@localhost test]$ readelf -S libmy.so
There are 27 section headers, starting at offset 0xad0:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
[ 0] NULL 00000000 000000 000000 00 0 0 0
[ 1] .gnu.hash GNU_HASH 000000d4 0000d4 00003c 04 A 2 0 4
[ 2] .dynsym DYNSYM 00000110 000110 000120 10 A 3 1 4
[ 3] .dynstr STRTAB 00000230 000230 000199 00 A 0 0 1
[ 4] .gnu.version VERSYM 000003ca 0003ca 000024 02 A 2 0 2
[ 5] .gnu.version_r VERNEED 000003f0 0003f0 000050 00 A 3 2 4
[ 6] .rel.dyn REL 00000440 000440 0000b0 08 A 2 0 4
[ 7] .rel.plt REL 000004f0 0004f0 000010 08 A 2 9 4
[ 8] .init PROGBITS 00000500 000500 000017 00 AX 0 0 4
[ 9] .plt PROGBITS 00000518 000518 000030 04 AX 0 0 4
[10] .text PROGBITS 00000550 000550 0001c4 00 AX 0 0 16
[11] .fini PROGBITS 00000714 000714 00001c 00 AX 0 0 4
[12] .rodata PROGBITS 00000730 000730 000006 00 A 0 0 1
[13] .eh_frame_hdr PROGBITS 00000738 000738 00002c 00 A 0 0 4
[14] .eh_frame PROGBITS 00000764 000764 000090 00 A 0 0 4
[15] .ctors PROGBITS 000017f4 0007f4 00000c 00 WA 0 0 4
[16] .dtors PROGBITS 00001800 000800 000008 00 WA 0 0 4
[17] .jcr PROGBITS 00001808 000808 000004 00 WA 0 0 4
[18] .data.rel.ro PROGBITS 0000180c 00080c 000004 00 WA 0 0 4
[19] .dynamic DYNAMIC 00001810 000810 0000e0 08 WA 3 0 4
[20] .got PROGBITS 000018f0 0008f0 00000c 04 WA 0 0 4
[21] .got.plt PROGBITS 000018fc 0008fc 000014 04 WA 0 0 4
[22] .bss NOBITS 00001910 000910 00000c 00 WA 0 0 4
[23] .comment PROGBITS 00000000 000910 0000e6 00 0 0 1
[24] .shstrtab STRTAB 00000000 0009f6 0000da 00 0 0 1
[25] .symtab SYMTAB 00000000 000f08 000410 10 26 48 4
[26] .strtab STRTAB 00000000 001318 000333 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific) 
