Linux Process Memory Model (1)

Is a simple memory model. Some segments are loaded from executable files. For the ing relationship between ELF sections and Segment, we can obtain related information from ELF Program Headers.

$ 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 incluaddr 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

In contrast, we can see that. text,. rodata,. data,. bss are loaded into the LOAD Segemtn segments 0x08048000, that is, 02 and 03. The Virtual Address in the ELF Section information is also a reference.

$ 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)

Note that not all sections are loaded into the process memory space.

View the memory information when the process is running:

(1) pmap

$ Ps aux | grep hello
Yueda 6649 0.0 1.6 39692 8404 pts/0 Sl + Dec10 vim hello. c
Yuhang 12787 0.0 0.0 1664 396 pts/1 S +./hello
Yuanyuan 12793 0.0 0.1 3036 796 pts/2 R + 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
0011316-0024e000 r-xp 00000000 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 5231/lib/tls/i686/cmov/libc-2.10.1.so
00251000-00254000 rw-p 00000000 0
002b2000-002cd000 r-xp 00000000 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 0 [vdso]
08048000-08049000 r-xp 00000000 135411/home/yujia/Projects/Learn. C/hello
08049000-0804a000 r -- p 00000000 08:01 135411/home/yujia/Projects/Learn. C/hello
0804a000-0804b000 rw-p 00001000 08:01 135411/home/yujia/Projects/Learn. C/hello
09f89000-09faa000 rw-p 00000000 00:00 0 [heap]
B7848000-b7849000 rw-p 00000000 0
B7855000-b7859000 rw-p 00000000 0
Bfc40000-bfc55000 rw-p 00000000 0 [stack]

(3) gdb

$ Gdb -- pid = 12787

(Gdb) info proc mappings

Process 12619
Export line = '/home/yujia/Projects/Learn. C/hello'
Cwd = '/home/yujia/Projects/Learn. c'
Exe = '/home/yujia/Projects/Learn. C/hello'
Mapped address spaces:

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