elf.s contains a custom ELF header, but no instructions. All of the machine
code comes out of rustc. (Although all of the instructions that survive
optimization went in as inline assembly.)
$ ./build.sh
Tested on rustc 1.0.0-dev (44a287e6e 2015-01-08 17:03:40 -0800)
You have rustc 1.0.0-dev (44a287e6e 2015-01-08 17:03:40 -0800)
Cloning into 'syscall.rs'...
Compiling syscall v0.1.0 (file:///home/keegan/tiny-rust-demo/syscall.rs)
+ rustc tinyrust.rs -O -C no-stack-check -C relocation-model=static -L syscall.rs/target
+ ar x libtinyrust.rlib tinyrust.o
+ objdump -dr tinyrust.o
tinyrust.o: file format elf64-x86-64
Disassembly of section .text.main:
0000000000000000 <main>:
0: b8 01 00 00 00 mov $0x1,%eax
5: bf 01 00 00 00 mov $0x1,%edi
a: be 08 00 40 00 mov $0x400008,%esi
f: ba 07 00 00 00 mov $0x7,%edx
14: 0f 05 syscall
16: b8 3c 00 00 00 mov $0x3c,%eax
1b: 31 ff xor %edi,%edi
1d: 0f 05 syscall
+ echo
+ ld --gc-sections -e main -T script.ld -o payload tinyrust.o
+ objcopy -j combined -O binary payload payload.bin
++ nm -f posix payload
++ grep '^main '
++ awk '{print $3}'
+ ENTRY=0000000000400078
+ set -x
+ nasm -f bin -o tinyrust -D entry=0x0000000000400078 elf.s
+ chmod +x tinyrust
+ hd tinyrust
00000000 7f 45 4c 46 02 01 01 00 48 65 6c 6c 6f 21 0a 00 |.ELF....Hello!..|
00000010 02 00 3e 00 01 00 00 00 78 00 40 00 00 00 00 00 |..>.....x.@.....|
00000020 40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |@...............|
00000030 00 00 00 00 40 00 38 00 01 00 00 00 00 00 00 00 |....@.8.........|
00000040 01 00 00 00 07 00 00 00 00 00 00 00 00 00 00 00 |................|
00000050 00 00 40 00 00 00 00 00 00 00 40 00 00 00 00 00 |..@.......@.....|
00000060 97 00 00 00 00 00 00 00 97 00 00 00 00 00 00 00 |................|
00000070 00 10 00 00 00 00 00 00 b8 01 00 00 00 bf 01 00 |................|
00000080 00 00 be 08 00 40 00 ba 07 00 00 00 0f 05 b8 3c |.....@.........<|
00000090 00 00 00 31 ff 0f 05 |...1...|
00000097
+ wc -c tinyrust
151 tinyrust
$ ./tinyrust
Hello!