Linux 进程内存模型 (1)

　　下图是一个简易的内存模型示意图。其中某些段 (Segment) 是从可执行文件加载的，有关 ELF Section 和 Segment 的映射关系，我们可以从 ELF Program Headers 中获取相关信息。

$ readelf -l hello
Elf file type is EXEC (Executable file)
Entry point 0x8048410
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
LOAD 0x000000 0x08048000 0x08048000 0x0064c 0x0064c R E 0x1000
LOAD 0x000f0c 0x08049f0c 0x08049f0c 0x0011c 0x00128 RW 0x1000
DYNAMIC 0x000f20 0x08049f20 0x08049f20 0x000d0 0x000d0 RW 0x4
NOTE 0x000148 0x08048148 0x08048148 0x00044 0x00044 R 0x4
GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0x4
GNU_RELRO 0x000f0c 0x08049f0c 0x08049f0c 0x000f4 0x000f4 R 0x1

Section to Segment mapping:
Segment Sections...
00
01 .interp
02 ... .init .plt .text .fini .rodata
03 ... .data .bss
04 .dynamic
05 .note.ABI-tag .note.gnu.build-id
06
07 .ctors .dtors .jcr .dynamic .got

对照示意图，我们可以看到 .text, .rodata, .data, .bss 被加载到 0x08048000 之后，也就是序号 02, 03 两个 LOAD Segemtn 段中。ELF Section 信息中的 Virtual Address 也是一个参考。

$ readelf -S hello
There are 38 section headers, starting at offset 0x1a10:

Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
... ...
[14] .text PROGBITS 08048410 000410 0001ec 00 AX 0 0 16
[16] .rodata PROGBITS 08048618 000618 000030 00 A 0 0 4
[24] .data PROGBITS 0804a018 001018 000010 00 WA 0 0 4
[25] .bss NOBITS 0804a028 001028 00000c 00 WA 0 0 4
[35] .shstrtab STRTAB 00000000 0018b8 000156 00 0 0 1
[36] .symtab SYMTAB 00000000 002000 000540 10 37 56 4
[37] .strtab STRTAB 00000000 002540 000263 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)

注意不是所有的 Section 都会被加载到进程内存空间。

查看进程运行时内存信息：

(1) pmap

$ ps aux | grep hello
yuhen 6649 0.0 1.6 39692 8404 pts/0 Sl+ Dec10 0:13 vim hello.c
yuhen 12787 0.0 0.0 1664 396 pts/1 S+ 08:24 0:00 ./hello
yuhen 12793 0.0 0.1 3036 796 pts/2 R+ 08:24 0:00 grep --color=auto hello

$ pmap -x 12787
12787: ./hello
Address Kbytes RSS Anon Locked Mode Mapping
00110000 1272 - - - r-x-- libc-2.10.1.so
0024e000 8 - - - r---- libc-2.10.1.so
00250000 4 - - - rw--- libc-2.10.1.so
00251000 12 - - - rw--- [ anon ]
002b2000 108 - - - r-x-- ld-2.10.1.so
002cd000 4 - - - r---- ld-2.10.1.so
002ce000 4 - - - rw--- ld-2.10.1.so
00c4d000 4 - - - r-x-- [ anon ]
08048000 4 - - - r-x-- hello
08049000 4 - - - r---- hello
0804a000 4 - - - rw--- hello
09f89000 132 - - - rw--- [ anon ]
b7848000 4 - - - rw--- [ anon ]
b7855000 16 - - - rw--- [ anon ]
bfc40000 84 - - - rw--- [ stack ]
-------- ------- ------- ------- -------
total kB 1664 - - -


(2) maps

$ cat /proc/12787/maps
00110000-0024e000 r-xp 00000000 08:01 5231 /lib/tls/i686/cmov/libc-2.10.1.so
0024e000-00250000 r--p 0013e000 08:01 5231 /lib/tls/i686/cmov/libc-2.10.1.so
00250000-00251000 rw-p 00140000 08:01 5231 /lib/tls/i686/cmov/libc-2.10.1.so
00251000-00254000 rw-p 00000000 00:00 0
002b2000-002cd000 r-xp 00000000 08:01 1809 /lib/ld-2.10.1.so
002cd000-002ce000 r--p 0001a000 08:01 1809 /lib/ld-2.10.1.so
002ce000-002cf000 rw-p 0001b000 08:01 1809 /lib/ld-2.10.1.so
00c4d000-00c4e000 r-xp 00000000 00:00 0 [vdso]
08048000-08049000 r-xp 00000000 08:01 135411 /home/yuhen/Projects/Learn.C/hello
08049000-0804a000 r--p 00000000 08:01 135411 /home/yuhen/Projects/Learn.C/hello
0804a000-0804b000 rw-p 00001000 08:01 135411 /home/yuhen/Projects/Learn.C/hello
09f89000-09faa000 rw-p 00000000 00:00 0 [heap]
b7848000-b7849000 rw-p 00000000 00:00 0
b7855000-b7859000 rw-p 00000000 00:00 0
bfc40000-bfc55000 rw-p 00000000 00:00 0 [stack]

(3) gdb

$ gdb --pid=12787

(gdb) info proc mappings

process 12619
cmdline = '/home/yuhen/Projects/Learn.C/hello'
cwd = '/home/yuhen/Projects/Learn.C'
exe = '/home/yuhen/Projects/Learn.C/hello'
Mapped address spaces:

Start Addr End Addr Size Offset objfile
... ...
0x8048000 0x8049000 0x1000 0 /home/yuhen/Projects/Learn.C/hello
0x8049000 0x804a000 0x1000 0 /home/yuhen/Projects/Learn.C/hello
0x804a000 0x804b000 0x1000 0x1000 /home/yuhen/Projects/Learn.C/hello
0x9f89000 0x9faa000 0x21000 0 [heap]
0xb7848000 0xb7849000 0x1000 0
0xb7855000 0xb7859000 0x4000 0
0xbfc40000 0xbfc55000 0x15000 0 [stack]

转自：http://www.rainsts.net/

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