Binutils LD创建巨大的文件 [英] Binutils LD creates huge files

问题描述

我正在尝试创建尽可能小的ELF.我创建了这样的测试文件(NASM语法):

I'm trying to create as small ELF as possible. I created a test file like this (NASM syntax):

SECTION .text
dd 0xdeadbeef

使用此链接描述文件:

SECTIONS {
    .text : {
        *(.text)
    }
}

然后我检查了平面二进制文件和ELF的大小，构建了两种方法:

Then I checked sizes of flat binary and ELFs built two ways:

nasm -f bin -o test test.asm

它是平面二进制，所以是4个字节.

It's flat binary, so 4 bytes.

nasm -f elf -o test.o test.asm
i686-elf-ld -Tlinker.ld test.o -o test

我希望最大可以达到500字节左右，但是生成的文件长4396字节！但是，有一个名为--strip-all的选项可以使该文件更小.

I'd expect something like 500 bytes max, but the resulting file is 4396 bytes long! There is an option however, named --strip-all, that could make this file smaller.

i686-elf-ld -Tlinker.ld test.o -o test --strip-all

4244字节.仍然很大.

4244 bytes. Still huge.

为什么LD生成这么大的文件?有没有办法缩小它?

Why is LD generating so big files? Is there a way to make it smaller?

推荐答案

链接器会将您的文本部分与最近的页面边界进行页面对齐，以便需求分页.

The linker is page aligning your text section to the nearest page boundary so that demand paging can be used.

$ objdump --headers -f test

test:     file format elf32-i386
architecture: i386, flags 0x00000102:
EXEC_P, D_PAGED
start address 0x00000000

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         00000004  00000000  00000000  00001000  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE

请注意，文本部分的对齐"列设置为4KB.由于将对齐方式设置为4Kb，并且正在使用按需分页(D_PAGED)，因此.text节位于文件的4Kb中.您的文字部分只有4个字节长.

Notice the "Align" column of the text section is set to 4KB. Because of the alignment is set to 4Kb and demand paging is in use (D_PAGED), the .text section is located 4Kb into the file. Your text section is only 4 bytes long.

与 -n 链接以禁用按需分页:

Link with -n to disable demand paging:

$ ld -Tlinker.ld test.o -o test --strip-all -n
$ objdump --headers -f test

test:     file format elf32-i386
architecture: i386, flags 0x00000002:
EXEC_P
start address 0x00000000

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         00000004  00000000  00000000  00000060  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
$ ls -l test
-rwxrwxr-x 1 mikel mikel 240 Apr 15 12:31 test

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