elf 文件初识-变量存储

收藏可参考的文章：https://www.cnblogs.com/LiuYanYGZ/p/5574602.html

.data 初始化过的全局变量 (含初始化静态变量)
.bss 未初始化的全局变量(包括函数内外的未初始化的静态变量)
.rodata 只读的变量（const）

1）关于常量和普通变量
int* const globle_A = 10; // .rodata
const int* globle_B = 10; // .data
2）关于初始化和非初始化

#include <stdio.h>

int global_dat1[30000]; //存储在bss段，由系统初始化为全 0，不需要存储初始化值
int global_dat1[30000]={0,}; //存储在bss段，由系统初始化为全 0，不需要存储初始化值 //是否是有优化的成分待继续追一下
int global_dat1[30000]={1,2,3,4,}; //存储在data 段，初始化的大数组要被存储，所以编译出来的文件会大很多！

int main(void)
{
return 0;
}

3）具体例子

编译 gcc para.c -g
然后读出 readelf -a a.out （readelf -s）

#include <stdio.h>

const int globle_A = 10; // .rodata  read only data 4006b8(start addr:4006b0 len:3a)

int globle_a = 20; // .data globle data 601040 (start addr:r601030 len:24)
int globle_b = 21; // .data 601044
static int static_c = 30; // .data 601048
static int static_d = 31; // .data 60104c

int c;  // .bss  uninit data area 60105c(start:601054)


void print_globle(void)
{
	printf(" %s: globle_a = %d \n", __FUNCTION__, globle_a );
}
int main(void)
{
static int static_local_e = 40; // .data 601050
static int static_local_f;  // .data 601058

int local_h = 70;

char globle_b[] = "Hello world";
int globle_a = 90;
register int c = 50;

printf(" %s: globle_a = %d \n", __FUNCTION__, globle_a );
//printf("Hello 1 %d\n", sizeof(A));
print_globle();

return 0;
}

ELF Header:
Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class:                             ELF64
Data:                              2's complement, little endian
Version:                           1 (current)
OS/ABI:                            UNIX - System V
ABI Version:                       0
Type:                              EXEC (Executable file)
Machine:                           Advanced Micro Devices X86-64
Version:                           0x1
Entry point address:               0x4004a0
Start of program headers:          64 (bytes into file)
Start of section headers:          8408 (bytes into file)
Flags:                             0x0
Size of this header:               64 (bytes)
Size of program headers:           56 (bytes)
Number of program headers:         9
Size of section headers:           64 (bytes)
Number of section headers:         36
Section header string table index: 33

Section Headers:
[Nr] Name              Type             Address           Offset
       Size              EntSize          Flags Link Info Align
[ 0]                   NULL             0000000000000000 00000000
       0000000000000000 0000000000000000           0     0     0
[ 1] .interp           PROGBITS         0000000000400238 00000238
       000000000000001c 0000000000000000   A       0     0     1
[ 2] .note.ABI-tag     NOTE             0000000000400254 00000254
       0000000000000020 0000000000000000   A       0     0     4
[ 3] .note.gnu.build-i NOTE             0000000000400274 00000274
       0000000000000024 0000000000000000   A       0     0     4
[ 4] .gnu.hash         GNU_HASH         0000000000400298 00000298
       000000000000001c 0000000000000000   A       5     0     8
[ 5] .dynsym           DYNSYM           00000000004002b8 000002b8
       0000000000000078 0000000000000018   A       6     1     8
[ 6] .dynstr           STRTAB           0000000000400330 00000330
       000000000000005a 0000000000000000   A       0     0     1
[ 7] .gnu.version      VERSYM           000000000040038a 0000038a
       000000000000000a 0000000000000002   A       5     0     2
[ 8] .gnu.version_r    VERNEED          0000000000400398 00000398
       0000000000000030 0000000000000000   A       6     1     8
[ 9] .rela.dyn         RELA             00000000004003c8 000003c8
       0000000000000018 0000000000000018   A       5     0     8
[10] .rela.plt         RELA             00000000004003e0 000003e0
       0000000000000048 0000000000000018 AI       5    24     8
[11] .init             PROGBITS         0000000000400428 00000428
       000000000000001a 0000000000000000 AX       0     0     4
[12] .plt              PROGBITS         0000000000400450 00000450
       0000000000000040 0000000000000010 AX       0     0     16
[13] .plt.got          PROGBITS         0000000000400490 00000490
       0000000000000008 0000000000000000 AX       0     0     8
[14] .text             PROGBITS         00000000004004a0 000004a0
       0000000000000202 0000000000000000 AX       0     0     16
[15] .fini             PROGBITS         00000000004006a4 000006a4
       0000000000000009 0000000000000000 AX       0     0     4
[16] .rodata           PROGBITS         00000000004006b0 000006b0
       000000000000003a 0000000000000000   A       0     0     8
[17] .eh_frame_hdr     PROGBITS         00000000004006ec 000006ec
       000000000000003c 0000000000000000   A       0     0     4
[18] .eh_frame         PROGBITS         0000000000400728 00000728
       0000000000000114 0000000000000000   A       0     0     8
[19] .init_array       INIT_ARRAY       0000000000600e10 00000e10
       0000000000000008 0000000000000000 WA       0     0     8
[20] .fini_array       FINI_ARRAY       0000000000600e18 00000e18
       0000000000000008 0000000000000000 WA       0     0     8
[21] .jcr              PROGBITS         0000000000600e20 00000e20
       0000000000000008 0000000000000000 WA       0     0     8
[22] .dynamic          DYNAMIC          0000000000600e28 00000e28
       00000000000001d0 0000000000000010 WA       6     0     8
[23] .got              PROGBITS         0000000000600ff8 00000ff8
       0000000000000008 0000000000000008 WA       0     0     8
[24] .got.plt          PROGBITS         0000000000601000 00001000
       0000000000000030 0000000000000008 WA       0     0     8
[25] .data             PROGBITS         0000000000601030 00001030
       0000000000000024 0000000000000000 WA       0     0     8
[26] .bss              NOBITS           0000000000601054 00001054
       000000000000000c 0000000000000000 WA       0     0     4
[27] .comment          PROGBITS         0000000000000000 00001054
       0000000000000035 0000000000000001 MS       0     0     1
[28] .debug_aranges    PROGBITS         0000000000000000 00001089
       0000000000000030 0000000000000000           0     0     1
[29] .debug_info       PROGBITS         0000000000000000 000010b9
       00000000000001f7 0000000000000000           0     0     1
[30] .debug_abbrev     PROGBITS         0000000000000000 000012b0
       00000000000000c4 0000000000000000           0     0     1
[31] .debug_line       PROGBITS         0000000000000000 00001374
       0000000000000048 0000000000000000           0     0     1
[32] .debug_str        PROGBITS         0000000000000000 000013bc
       0000000000000130 0000000000000001 MS       0     0     1
[33] .shstrtab         STRTAB           0000000000000000 00001f87
       000000000000014c 0000000000000000           0     0     1
[34] .symtab           SYMTAB           0000000000000000 000014f0
       00000000000007e0 0000000000000018          35    58     8
[35] .strtab           STRTAB           0000000000000000 00001cd0
       00000000000002b7 0000000000000000           0     0     1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), l (large)
I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)

There are no section groups in this file.

Program Headers:
Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags Align
PHDR           0x0000000000000040 0x0000000000400040 0x0000000000400040
                 0x00000000000001f8 0x00000000000001f8 R E    8
INTERP         0x0000000000000238 0x0000000000400238 0x0000000000400238
                 0x000000000000001c 0x000000000000001c R      1
      [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
LOAD           0x0000000000000000 0x0000000000400000 0x0000000000400000
                 0x000000000000083c 0x000000000000083c R E    200000
LOAD           0x0000000000000e10 0x0000000000600e10 0x0000000000600e10
                 0x0000000000000244 0x0000000000000250 RW     200000
DYNAMIC        0x0000000000000e28 0x0000000000600e28 0x0000000000600e28
                 0x00000000000001d0 0x00000000000001d0 RW     8
NOTE           0x0000000000000254 0x0000000000400254 0x0000000000400254
                 0x0000000000000044 0x0000000000000044 R      4
GNU_EH_FRAME   0x00000000000006ec 0x00000000004006ec 0x00000000004006ec
                 0x000000000000003c 0x000000000000003c R      4
GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000 RW     10
GNU_RELRO      0x0000000000000e10 0x0000000000600e10 0x0000000000600e10
                 0x00000000000001f0 0x00000000000001f0 R      1

Section to Segment mapping:
Segment Sections...
   00
   01     .interp
   02     .interp .note.ABI-tag .note.gnu.build-id .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt .init .plt .plt.got .text .fini .rodata .eh_frame_hdr .eh_frame
   03     .init_array .fini_array .jcr .dynamic .got .got.plt .data .bss
   04     .dynamic
   05     .note.ABI-tag .note.gnu.build-id
   06     .eh_frame_hdr
   07
   08     .init_array .fini_array .jcr .dynamic .got

Dynamic section at offset 0xe28 contains 24 entries:
Tag        Type                         Name/Value
0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
0x000000000000000c (INIT)               0x400428
0x000000000000000d (FINI)               0x4006a4
0x0000000000000019 (INIT_ARRAY)         0x600e10
0x000000000000001b (INIT_ARRAYSZ)       8 (bytes)
0x000000000000001a (FINI_ARRAY)         0x600e18
0x000000000000001c (FINI_ARRAYSZ)       8 (bytes)
0x000000006ffffef5 (GNU_HASH)           0x400298
0x0000000000000005 (STRTAB)             0x400330
0x0000000000000006 (SYMTAB)             0x4002b8
0x000000000000000a (STRSZ)              90 (bytes)
0x000000000000000b (SYMENT)             24 (bytes)
0x0000000000000015 (DEBUG)              0x0
0x0000000000000003 (PLTGOT)             0x601000
0x0000000000000002 (PLTRELSZ)           72 (bytes)
0x0000000000000014 (PLTREL)             RELA
0x0000000000000017 (JMPREL)             0x4003e0
0x0000000000000007 (RELA)               0x4003c8
0x0000000000000008 (RELASZ)             24 (bytes)
0x0000000000000009 (RELAENT)            24 (bytes)
0x000000006ffffffe (VERNEED)            0x400398
0x000000006fffffff (VERNEEDNUM)         1
0x000000006ffffff0 (VERSYM)             0x40038a
0x0000000000000000 (NULL)               0x0

Relocation section '.rela.dyn' at offset 0x3c8 contains 1 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000600ff8 000400000006 R_X86_64_GLOB_DAT 0000000000000000 __gmon_start__ + 0

Relocation section '.rela.plt' at offset 0x3e0 contains 3 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000601018 000100000007 R_X86_64_JUMP_SLO 0000000000000000 __stack_chk_fail@GLIBC_2.4 + 0
000000601020 000200000007 R_X86_64_JUMP_SLO 0000000000000000 printf@GLIBC_2.2.5 + 0
000000601028 000300000007 R_X86_64_JUMP_SLO 0000000000000000 __libc_start_main@GLIBC_2.2.5 + 0

The decoding of unwind sections for machine type Advanced Micro Devices X86-64 is not currently supported.

Symbol table '.dynsym' contains 5 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE LOCAL DEFAULT UND
     1: 0000000000000000     0 FUNC    GLOBAL DEFAULT UND __stack_chk_fail@GLIBC_2.4 (2)
     2: 0000000000000000     0 FUNC    GLOBAL DEFAULT UND printf@GLIBC_2.2.5 (3)
     3: 0000000000000000     0 FUNC    GLOBAL DEFAULT UND __libc_start_main@GLIBC_2.2.5 (3)
     4: 0000000000000000     0 NOTYPE WEAK   DEFAULT UND __gmon_start__

Symbol table '.symtab' contains 84 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE LOCAL DEFAULT UND
     1: 0000000000400238     0 SECTION LOCAL DEFAULT    1
     2: 0000000000400254     0 SECTION LOCAL DEFAULT    2
     3: 0000000000400274     0 SECTION LOCAL DEFAULT    3
     4: 0000000000400298     0 SECTION LOCAL DEFAULT    4
     5: 00000000004002b8     0 SECTION LOCAL DEFAULT    5
     6: 0000000000400330     0 SECTION LOCAL DEFAULT    6
     7: 000000000040038a     0 SECTION LOCAL DEFAULT    7
     8: 0000000000400398     0 SECTION LOCAL DEFAULT    8
     9: 00000000004003c8     0 SECTION LOCAL DEFAULT    9
    10: 00000000004003e0     0 SECTION LOCAL DEFAULT   10
    11: 0000000000400428     0 SECTION LOCAL DEFAULT   11
    12: 0000000000400450     0 SECTION LOCAL DEFAULT   12
    13: 0000000000400490     0 SECTION LOCAL DEFAULT   13
    14: 00000000004004a0     0 SECTION LOCAL DEFAULT   14
    15: 00000000004006a4     0 SECTION LOCAL DEFAULT   15
    16: 00000000004006b0     0 SECTION LOCAL DEFAULT   16
    17: 00000000004006ec     0 SECTION LOCAL DEFAULT   17
    18: 0000000000400728     0 SECTION LOCAL DEFAULT   18
    19: 0000000000600e10     0 SECTION LOCAL DEFAULT   19
    20: 0000000000600e18     0 SECTION LOCAL DEFAULT   20
    21: 0000000000600e20     0 SECTION LOCAL DEFAULT   21
    22: 0000000000600e28     0 SECTION LOCAL DEFAULT   22
    23: 0000000000600ff8     0 SECTION LOCAL DEFAULT   23
    24: 0000000000601000     0 SECTION LOCAL DEFAULT   24
    25: 0000000000601030     0 SECTION LOCAL DEFAULT   25
    26: 0000000000601054     0 SECTION LOCAL DEFAULT   26
    27: 0000000000000000     0 SECTION LOCAL DEFAULT   27
    28: 0000000000000000     0 SECTION LOCAL DEFAULT   28
    29: 0000000000000000     0 SECTION LOCAL DEFAULT   29
    30: 0000000000000000     0 SECTION LOCAL DEFAULT   30
    31: 0000000000000000     0 SECTION LOCAL DEFAULT   31
    32: 0000000000000000     0 SECTION LOCAL DEFAULT   32
    33: 0000000000000000     0 FILE    LOCAL DEFAULT ABS crtstuff.c
    34: 0000000000600e20     0 OBJECT LOCAL DEFAULT   21 __JCR_LIST__
    35: 00000000004004d0     0 FUNC    LOCAL DEFAULT   14 deregister_tm_clones
    36: 0000000000400510     0 FUNC    LOCAL DEFAULT   14 register_tm_clones
    37: 0000000000400550     0 FUNC    LOCAL DEFAULT   14 __do_global_dtors_aux
    38: 0000000000601054     1 OBJECT LOCAL DEFAULT   26 completed.7594
    39: 0000000000600e18     0 OBJECT LOCAL DEFAULT   20 __do_global_dtors_aux_fin
    40: 0000000000400570     0 FUNC    LOCAL DEFAULT   14 frame_dummy
    41: 0000000000600e10     0 OBJECT LOCAL DEFAULT   19 __frame_dummy_init_array_
    42: 0000000000000000     0 FILE    LOCAL DEFAULT ABS para.c
    43: 0000000000601048     4 OBJECT LOCAL DEFAULT   25 static_c
    44: 000000000060104c     4 OBJECT LOCAL DEFAULT   25 static_d
    45: 00000000004006d8    13 OBJECT LOCAL DEFAULT   16 __FUNCTION__.2292
    46: 00000000004006e5     5 OBJECT LOCAL DEFAULT   16 __FUNCTION__.2302
    47: 0000000000601058     4 OBJECT LOCAL DEFAULT   26 static_local_f.2297
    48: 0000000000601050     4 OBJECT LOCAL DEFAULT   25 static_local_e.2296
    49: 0000000000000000     0 FILE    LOCAL DEFAULT ABS crtstuff.c
    50: 0000000000400838     0 OBJECT LOCAL DEFAULT   18 __FRAME_END__
    51: 0000000000600e20     0 OBJECT LOCAL DEFAULT   21 __JCR_END__
    52: 0000000000000000     0 FILE    LOCAL DEFAULT ABS
    53: 0000000000600e18     0 NOTYPE LOCAL DEFAULT   19 __init_array_end
    54: 0000000000600e28     0 OBJECT LOCAL DEFAULT   22 _DYNAMIC
    55: 0000000000600e10     0 NOTYPE LOCAL DEFAULT   19 __init_array_start
    56: 00000000004006ec     0 NOTYPE LOCAL DEFAULT   17 __GNU_EH_FRAME_HDR
    57: 0000000000601000     0 OBJECT LOCAL DEFAULT   24 _GLOBAL_OFFSET_TABLE_
    58: 00000000004006a0     2 FUNC    GLOBAL DEFAULT   14 __libc_csu_fini
    59: 0000000000000000     0 NOTYPE WEAK   DEFAULT UND _ITM_deregisterTMCloneTab
    60: 0000000000601030     0 NOTYPE WEAK   DEFAULT   25 data_start
    61: 0000000000601054     0 NOTYPE GLOBAL DEFAULT   25 _edata
    62: 00000000004006a4     0 FUNC    GLOBAL DEFAULT   15 _fini
    63: 0000000000000000     0 FUNC    GLOBAL DEFAULT UND __stack_chk_fail@@GLIBC_2
    64: 0000000000000000     0 FUNC    GLOBAL DEFAULT UND printf@@GLIBC_2.2.5
    65: 0000000000000000     0 FUNC    GLOBAL DEFAULT UND __libc_start_main@@GLIBC_
    66: 0000000000601030     0 NOTYPE GLOBAL DEFAULT   25 __data_start
    67: 0000000000000000     0 NOTYPE WEAK   DEFAULT UND __gmon_start__
    68: 0000000000601040     4 OBJECT GLOBAL DEFAULT   25 globle_a
    69: 0000000000601038     0 OBJECT GLOBAL HIDDEN    25 __dso_handle
    70: 00000000004006b0     4 OBJECT GLOBAL DEFAULT   16 _IO_stdin_used
    71: 00000000004006b8     4 OBJECT GLOBAL DEFAULT   16 globle_A
    72: 0000000000400630   101 FUNC    GLOBAL DEFAULT   14 __libc_csu_init
    73: 0000000000601060     0 NOTYPE GLOBAL DEFAULT   26 _end
    74: 00000000004004a0    42 FUNC    GLOBAL DEFAULT   14 _start
    75: 000000000060105c     4 OBJECT GLOBAL DEFAULT   26 c
    76: 0000000000601054     0 NOTYPE GLOBAL DEFAULT   26 __bss_start
    77: 00000000004005b9   115 FUNC    GLOBAL DEFAULT   14 main
    78: 0000000000400596    35 FUNC    GLOBAL DEFAULT   14 print_globle
    79: 0000000000000000     0 NOTYPE WEAK   DEFAULT UND _Jv_RegisterClasses
    80: 0000000000601058     0 OBJECT GLOBAL HIDDEN    25 __TMC_END__
    81: 0000000000000000     0 NOTYPE WEAK   DEFAULT UND _ITM_registerTMCloneTable
    82: 0000000000400428     0 FUNC    GLOBAL DEFAULT   11 _init
    83: 0000000000601044     4 OBJECT GLOBAL DEFAULT   25 globle_b

Version symbols section '.gnu.version' contains 5 entries:
Addr: 000000000040038a Offset: 0x00038a Link: 5 (.dynsym)
000: 0 (*local*) 2 (GLIBC_2.4) 3 (GLIBC_2.2.5) 3 (GLIBC_2.2.5)
004: 0 (*local*)

Version needs section '.gnu.version_r' contains 1 entries:
Addr: 0x0000000000400398 Offset: 0x000398 Link: 6 (.dynstr)
000000: Version: 1 File: libc.so.6 Cnt: 2
0x0010: Name: GLIBC_2.2.5 Flags: none Version: 3
0x0020: Name: GLIBC_2.4 Flags: none Version: 2

Displaying notes found at file offset 0x00000254 with length 0x00000020:
Owner                 Data size       Description
GNU                  0x00000010       NT_GNU_ABI_TAG (ABI version tag)
    OS: Linux, ABI: 2.6.32

Displaying notes found at file offset 0x00000274 with length 0x00000024:
Owner                 Data size       Description
GNU                  0x00000014       NT_GNU_BUILD_ID (unique build ID bitstring)
    Build ID: 55ab69f6327e884925a448bcf65acbaa59cc07a9

elf 文件初识-变量存储

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