为什么Linux/gnu链接器选择地址0x400000? [英] Why Linux/gnu linker chose address 0x400000?
问题描述
我正在在Linux x86_64上试用ELF可执行文件和gnu工具链:
I'm experimenting with ELF executables and the gnu toolchain on Linux x86_64:
我已经链接并手动剥离了"Hello World"测试.
I've linked and stripped (by hand) a "Hello World" test.s:
.global _start
.text
_start:
mov $1, %rax
...
放入267字节的ELF64可执行文件...
into a 267 byte ELF64 executable...
0000000: 7f45 4c46 0201 0100 0000 0000 0000 0000 .ELF............
0000010: 0200 3e00 0100 0000 d400 4000 0000 0000 ..>.......@.....
0000020: 4000 0000 0000 0000 0000 0000 0000 0000 @...............
0000030: 0000 0000 4000 3800 0100 4000 0000 0000 ....@.8...@.....
0000040: 0100 0000 0500 0000 0000 0000 0000 0000 ................
0000050: 0000 4000 0000 0000 0000 4000 0000 0000 ..@.......@.....
0000060: 0b01 0000 0000 0000 0b01 0000 0000 0000 ................
0000070: 0000 2000 0000 0000 0000 0000 0000 0000 .. .............
0000080: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0000090: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00000a0: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00000b0: 0400 0000 1400 0000 0300 0000 474e 5500 ............GNU.
00000c0: c3b0 cbbd 0abf a73c 26ef e960 fc64 4026 .......<&..`.d@&
00000d0: e242 8bc7 48c7 c001 0000 0048 c7c7 0100 .B..H......H....
00000e0: 0000 48c7 c6fe 0040 0048 c7c2 0d00 0000 ..H....@.H......
00000f0: 0f05 48c7 c03c 0000 0048 31ff 0f05 4865 ..H..<...H1...He
0000100: 6c6c 6f2c 2057 6f72 6c64 0a llo, World.
它只有一个程序头(LOAD),没有任何节:
It has one program header (LOAD) and no sections:
There are 1 program headers, starting at offset 64
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x0000000000400000 0x0000000000400000
0x000000000000010b 0x000000000000010b R E 200000
这似乎会在地址0x400000处加载整个文件(文件偏移量0到0x10b-elf报头).
This seems to load the entire file (file offset 0 thru 0x10b - elf header and all) at address 0x400000.
入口点是:
Entry point address: 0x4000d4
与文件中的0xd4偏移量相对应,并且我们可以看到地址是机器代码(mov $1, %rax1
)的开头
Which corresponds to 0xd4 offset in the file, and as we can see that address is the start of the machine code (mov $1, %rax1
)
我的问题是,gnu链接程序为什么(如何)选择地址0x400000
将该文件映射到?
My question is why (how) did the gnu linker choose address 0x400000
to map the file to?
推荐答案
起始地址通常由链接描述文件设置.
The start address is usually set by a linker script.
例如,在GNU/Linux上,我们看到/usr/lib/ldscripts/elf_x86_64.x
:
For example, on GNU/Linux, looking at /usr/lib/ldscripts/elf_x86_64.x
we see:
...
PROVIDE (__executable_start = SEGMENT_START("text-segment", 0x400000)); \
. = SEGMENT_START("text-segment", 0x400000) + SIZEOF_HEADERS;
值0x400000
是此平台上SEGMENT_START()
函数的默认值.
The value 0x400000
is the default value for the SEGMENT_START()
function on this platform.
您可以通过浏览链接器手册找到有关链接器脚本的更多信息:
You can find out more about linker scripts by browsing the linker manual:
% info ld Scripts
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