assembly - How to make an executable ELF file in Linux using a hex editor?

Just curious. This obviously isn't a very good solution for actual programming, but say I wanted to make an executable in Bless (a hex editor).

My architecture is x86. What's a very simple program I can make? A hello world? An infinite loop? Similar to this question, but in Linux.

Answer

As mentioned in my comment, you will essentially be writing your own elf-header for the executable eliminating the unneeded sections. There are still several required sections. The documentation at Muppetlabs-TinyPrograms does a fair job explaining this process. For fun, here are a couple of examples:

The equivalent of /bin/true (45 bytes):

00000000  7F 45 4C 46 01 00 00 00  00 00 00 00 00 00 49 25  |.ELF..........I%|
00000010  02 00 03 00 1A 00 49 25  1A 00 49 25 04 00 00 00  |......I%..I%....|
00000020  5B 5F F2 AE 40 22 5F FB  CD 80 20 00 01           |[_..@"_... ..|
0000002d

Your classic 'Hello World!' (160 bytes):

00000000  7f 45 4c 46 01 01 01 03  00 00 00 00 00 00 00 00  |.ELF............|
00000010  02 00 03 00 01 00 00 00  74 80 04 08 34 00 00 00  |........t...4...|
00000020  00 00 00 00 00 00 00 00  34 00 20 00 02 00 28 00  |........4. ...(.|
00000030  00 00 00 00 01 00 00 00  74 00 00 00 74 80 04 08  |........t...t...|
00000040  74 80 04 08 1f 00 00 00  1f 00 00 00 05 00 00 00  |t...............|
00000050  00 10 00 00 01 00 00 00  93 00 00 00 93 90 04 08  |................|
00000060  93 90 04 08 0d 00 00 00  0d 00 00 00 06 00 00 00  |................|
00000070  00 10 00 00 b8 04 00 00  00 bb 01 00 00 00 b9 93  |................|

00000080  90 04 08 ba 0d 00 00 00  cd 80 b8 01 00 00 00 31  |...............1|
00000090  db cd 80 48 65 6c 6c 6f  20 77 6f 72 6c 64 21 0a  |...Hello world!.|
000000a0

Don't forget to make them executable...