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| ELF file .text section file offset https://forum.osdev.org/viewtopic.php?f=1&t=31438 |
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| Author: | alexhoppus [ Sun Mar 19, 2017 2:00 am ] |
| Post subject: | ELF file .text section file offset |
Hey. I use this https://github.com/alexhoppus/rpios/blob/master/user/Makefile Makefile to build this https://github.com/alexhoppus/rpios/blob/master/user/app1.c application with the use of this https://github.com/alexhoppus/rpios/blob/master/user/linker.ld linker script. After building it turned out that the size of this app is abnormally huge, currently I tested it on Ubuntu 16.04/14.04 and for different versions of arm-none-eabi-* toolchain it gives 70K/35K appropriately. The reason of such a big size of ELF file is that .text section is placed inside ELF file with a big offset: Code: user (master) $ arm-linux-gnueabi-readelf --sections app1 | grep .text [ 1] .text PROGBITS 00800000 008000 000078 00 AX 0 0 4 As you can see in this case .text section is located at offset 0x8000 inside ELF file. The space between ELF header and text section is filled with zeros. Code: user (master) $ hexdump -C ./app1 | less Code: 00000000 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 |.ELF............| 00000010 02 00 28 00 01 00 00 00 00 00 80 00 34 00 00 00 |..(.........4...| 00000020 5c 81 00 00 02 02 00 05 34 00 20 00 01 00 28 00 |\.......4. ...(.| 00000030 09 00 06 00 01 00 00 00 00 80 00 00 00 00 80 00 |................| 00000040 00 00 80 00 b8 00 00 00 b8 00 00 00 05 00 00 00 |................| 00000050 00 80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00000060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00008000 00 00 a0 e3 00 10 a0 e3 1a 00 00 ea 04 40 2d e5 |.............@-.| 00008010 03 40 a0 e1 02 30 a0 e1 01 20 a0 e1 00 10 a0 e1 |[email protected]... ......| 00008020 01 00 a0 e3 00 00 00 ef 04 40 9d e4 1e ff 2f e1 |.........@..../.| 00008030 04 40 2d e5 03 40 a0 e1 02 30 a0 e1 01 20 a0 e1 |.@[email protected]... ..| I use this application from inside of my self-written OS and this app is linked as a data blob with the kernel image. The kernel is loaded using UART bootloader that's why the final image size is critical. Also as you have guessed i use ELF loader for apps so preserving ELF format is important for me. The question is - why this text section offset is so huge, what is the reason for this? And how can i control it? Actually, i have found the similar question on SO, but it is unanswered http://stackoverflow.com/questions/26834470/controlling-file-offset-in-linking |
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| Author: | alexfru [ Sun Mar 19, 2017 2:53 am ] |
| Post subject: | Re: ELF file .text section file offset |
I have not tried these, but there seem to be a few clues:
If you're really concerned about the size, then either you should use a different format or simply compress the file. |
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| Author: | lkurusa [ Sun Mar 19, 2017 12:35 pm ] |
| Post subject: | Re: ELF file .text section file offset |
What is in your ".text.boot" section? |
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| Author: | zaval [ Sun Mar 19, 2017 3:40 pm ] |
| Post subject: | Re: ELF file .text section file offset |
show your readelf -l output |
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| Author: | bzt [ Tue Mar 21, 2017 1:36 pm ] |
| Post subject: | Re: ELF file .text section file offset |
I had the same issue. It's --nmagic you need. The GNU linker documentation does not mention it, but it also sets alignment. |
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