一、首先看一个简单的程序：
#include<stdlib.h>
int main()
{
while(1)
{
sleep(1000);
}
return 0;
}
gcc -static SectionMapping.c -o SectionMapping.elf
/usr/bin/ld: cannot find
-lc
yum install glibc-static
查看一下静态链接之后，SectionMapping.elf的段分布情况
readelf -S SectionMapping.elf
There are 34 section headers, starting at offset 0xd0aa0:
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .note.ABI-tag NOTE 0000000000400190 00000190
0000000000000020 0000000000000000 A 0 0 4
[ 2] .note.gnu.build-i NOTE 00000000004001b0 000001b0
0000000000000024 0000000000000000 A 0 0 4
[ 3] .rela.plt RELA 00000000004001d8 000001d8
0000000000000108 0000000000000018 AI 0 25 8
[ 4] .init PROGBITS 00000000004002e0 000002e0
000000000000001a 0000000000000000 AX 0 0 4
[ 5] .plt PROGBITS 0000000000400300 00000300
00000000000000b0 0000000000000000 AX 0 0 16
[ 6] .text PROGBITS 00000000004003b0 000003b0
0000000000091916 0000000000000000 AX 0 0 16
[ 7] __libc_thread_fre PROGBITS 0000000000491cd0 00091cd0
00000000000000b2 0000000000000000 AX 0 0 16
[ 8] __libc_freeres_fn PROGBITS 0000000000491d90 00091d90
0000000000001aef 0000000000000000 AX 0 0 16
[ 9] .fini PROGBITS 0000000000493880 00093880
0000000000000009 0000000000000000 AX 0 0 4
[10] .rodata PROGBITS 00000000004938a0 000938a0
00000000000196f8 0000000000000000 A 0 0 32
[11] .stapsdt.base PROGBITS 00000000004acf98 000acf98
0000000000000001 0000000000000000 A 0 0 1
[12] __libc_thread_sub PROGBITS 00000000004acfa0 000acfa0
0000000000000008 0000000000000000 A 0 0 8
[13] __libc_subfreeres PROGBITS 00000000004acfa8 000acfa8
0000000000000050 0000000000000000 A 0 0 8
[14] __libc_IO_vtables PROGBITS 00000000004ad000 000ad000
00000000000006a8 0000000000000000 A 0 0 32
[15] __libc_atexit PROGBITS 00000000004ad6a8 000ad6a8
0000000000000008 0000000000000000 A 0 0 8
[16] .eh_frame PROGBITS 00000000004ad6b0 000ad6b0
000000000000e234 0000000000000000 A 0 0 8
[17] .gcc_except_table PROGBITS 00000000004bb8e4 000bb8e4
0000000000000105 0000000000000000 A 0 0 1
[18] .tdata PROGBITS 00000000006bbeb0 000bbeb0
0000000000000020 0000000000000000 WAT 0 0 16
[19] .tbss NOBITS 00000000006bbed0 000bbed0
0000000000000038 0000000000000000 WAT 0 0 16
[20] .init_array INIT_ARRAY 00000000006bbed0 000bbed0
0000000000000010 0000000000000008 WA 0 0 8
[21] .fini_array FINI_ARRAY 00000000006bbee0 000bbee0
0000000000000010 0000000000000008 WA 0 0 8
[22] .jcr PROGBITS 00000000006bbef0 000bbef0
0000000000000008 0000000000000000 WA 0 0 8
[23] .data.rel.ro PROGBITS 00000000006bbf00 000bbf00
00000000000000e4 0000000000000000 WA 0 0 32
[24] .got PROGBITS 00000000006bbfe8 000bbfe8
0000000000000008 0000000000000008 WA 0 0 8
[25] .got.plt PROGBITS 00000000006bc000 000bc000
0000000000000070 0000000000000008 WA 0 0 8
[26] .data PROGBITS 00000000006bc080 000bc080
0000000000001690 0000000000000000 WA 0 0 32
[27] .bss NOBITS 00000000006bd720 000bd710
0000000000002158 0000000000000000 WA 0 0 32
[28] __libc_freeres_pt NOBITS 00000000006bf878 000bd710
0000000000000030 0000000000000000 WA 0 0 8
[29] .comment PROGBITS 0000000000000000 000bd710
000000000000002d 0000000000000001 MS 0 0 1
[30] .note.stapsdt NOTE 0000000000000000 000bd740
0000000000000f88 0000000000000000 0 0 4
[31] .symtab SYMTAB 0000000000000000 000be6c8
000000000000b9e8 0000000000000018 32 815 8
[32] .strtab STRTAB 0000000000000000 000ca0b0
0000000000006870 0000000000000000 0 0 1
[33] .shstrtab STRTAB 0000000000000000 000d0920
000000000000017b 0000000000000000 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
l (large), p (processor specific)
可执行文件中共有33个段。
readelf -l SectionMapping.elf: 查看elf文件的Segment 即程序头。它描述ELF文件该如何被映射到进程的虚拟地址空间
Elf file type is EXEC (Executable file)
Entry point 0x400ecd
There are 6 program headers, starting at offset 64
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x0000000000400000 0x0000000000400000
0x00000000000bb9e9 0x00000000000bb9e9 R E 200000
LOAD 0x00000000000bbeb0 0x00000000006bbeb0 0x00000000006bbeb0
0x0000000000001860 0x00000000000039f8 RW 200000
NOTE 0x0000000000000190 0x0000000000400190 0x0000000000400190
0x0000000000000044 0x0000000000000044 R 4
TLS 0x00000000000bbeb0 0x00000000006bbeb0 0x00000000006bbeb0
0x0000000000000020 0x0000000000000058 R 10
GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 RW 10
GNU_RELRO 0x00000000000bbeb0 0x00000000006bbeb0 0x00000000006bbeb0
0x0000000000000150 0x0000000000000150 R 1
Section to Segment mapping:
Segment Sections...
00 .note.ABI-tag .note.gnu.build-id .rela.plt .init .plt .text __libc_thread_freeres_fn __libc_freeres_fn .fini .rodata .stapsdt.base __libc_thread_subfreeres __libc_subfreeres __libc_IO_vtables __libc_atexit .eh_frame .gcc_except_table
01 .tdata .init_array .fini_array .jcr .data.rel.ro .got .got.plt .data .bss __libc_freeres_ptrs
02 .note.ABI-tag .note.gnu.build-id
03 .tdata .tbss
04
05 .tdata .init_array .fini_array .jcr .data.rel.ro .got
二、堆和栈
在操作系统中，VMA除了被用来映射可执行文件中的各个"segment"以外，他还可以有其他作用。操作系统通过使用VMA来管理进程的地址空间。程序执行时，要用到栈和堆，事实上，它们也是以VMA的形式存在。一般情况，一个进程中的栈和堆分别都有一个对应的VMA。在Linux中可以由/proc查看：
./SectionMapping.elf &
[1] 59117
[root@tlinux /]# cat /proc/59117/maps
00400000-004bc000 r-xp 00000000 08:05 4456 /SectionMapping.elf 006bb000-006be000 rw-p 000bb000 08:05 4456 /SectionMapping.elf 006be000-006c0000 rw-p 00000000 00:00 0 017e1000-01804000 rw-p 00000000 00:00 0 [heap] 7ffc12ce6000-7ffc12d07000 rw-p 00000000 00:00 0 [stack] 7ffc12db7000-7ffc12db9000 r-xp 00000000 00:00 0 [vdso] ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
输出中：第一列是VMA地址范围，第二列是VMA权限，“p”表示私有，“s”表示共享。第三列是偏移。表示VMA对应的Segment在映像文件中的偏移。第四列是映像文件的主设备号与次设备号。第五列表示文件结点。