elf.s contains a custom ELF header, but no instructions.
All of the machine code comes out of rustc.
(While most of the operations originate from inline assembly, LLVM replaces the instructions with more compact ones!)
This project is built by running the ./build.sh script instead of cargo build: Making the binary this small requires post-processing steps which cargo doesn't support.
Requires nightly Rust because it uses inline assembly (through the sc crate) to make direct system calls.
Blog post about this demo, by Keegan McAllister who originally created it.
$ ./build.sh
Tested on rustc 1.46.0-nightly (346aec9b0 2020-07-11)
You have rustc 1.46.0-nightly (346aec9b0 2020-07-11)
+ cargo build --release --verbose
Downloaded sc v0.2.3
Downloaded 1 crate (37.2 KB) in 0.71s
Compiling sc v0.2.3
Running `rustc --crate-name sc /home/tormol/.cargo/registry/src/github.com-1ecc6299db9ec823/sc-0.2.3/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts --crate-type lib --emit=dep-info,metadata,link -C opt-level=z -C panic=abort -Cembed-bitcode=no -C metadata=8fa96b43c9d094b0 -C extra-filename=-8fa96b43c9d094b0 --out-dir /home/tormol/p/rust/tiny-rust-demo/target/release/deps -L dependency=/home/tormol/p/rust/tiny-rust-demo/target/release/deps --cap-lints allow -C relocation-model=static`
Compiling tiny-rust-executable v0.5.0 (/home/tormol/p/rust/tiny-rust-executable)
Running `rustc --crate-name tinyrust tinyrust.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type lib --emit=dep-info,metadata,link -C opt-level=z -C panic=abort -Clinker-plugin-lto -C metadata=61b6ba1ff0efe210 -C extra-filename=-61b6ba1ff0efe210 --out-dir /home/tormol/p/rust/tiny-rust-executable/target/release/deps -L dependency=/home/tormol/p/rust/tiny-rust-executable/target/release/deps --extern sc=/home/tormol/p/rust/tiny-rust-executable/target/release/deps/libsc-35c3430f33082929.rmeta -C relocation-model=static`
Finished release [optimized] target(s) in 0.45s
++ ar t libtinyrust.rlib
++ grep '.o$'
+ OBJECT=tinyrust.tinyrust.3a1fbbbh-cgu.0.rcgu.o
+ ar x libtinyrust.rlib tinyrust.tinyrust.3a1fbbbh-cgu.0.rcgu.o
+ objdump -dr tinyrust.tinyrust.3a1fbbbh-cgu.0.rcgu.o
tinyrust.tinyrust.3a1fbbbh-cgu.0.rcgu.o: file format elf64-x86-64
Disassembly of section .text.main:
0000000000000000 <main>:
0: 6a 07 pushq $0x7
2: 5a pop %rdx
3: 6a 01 pushq $0x1
5: 58 pop %rax
6: be 08 00 40 00 mov $0x400008,%esi
b: 48 89 c7 mov %rax,%rdi
e: 0f 05 syscall
10: 6a 3c pushq $0x3c
12: 58 pop %rax
13: 31 ff xor %edi,%edi
15: 0f 05 syscall
17: 0f 0b ud2
+ echo
+ ld --gc-sections -e main -T script.ld -o payload tinyrust.tinyrust.3a1fbbbh-cgu.0.rcgu.o
+ objcopy -j combined -O binary payload payload.bin
++ nm --format=posix payload
++ grep '^main '
++ awk '{print $3}'
+ ENTRY=0000000000400070
+ nasm -f bin -o tinyrust -D entry=0x0000000000400070 elf.s
+ chmod +x tinyrust
+ hexdump -C tinyrust
00000000 7f 45 4c 46 02 01 01 09 48 65 6c 6c 6f 21 0a 00 |.ELF....Hello!..|
00000010 02 00 3e 00 01 00 00 00 70 00 40 00 00 00 00 00 |..>.....p.@.....|
00000020 38 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |8...............|
00000030 00 00 00 00 38 00 38 00 01 00 00 00 07 00 00 00 |....8.8.........|
00000040 00 00 00 00 00 00 00 00 00 00 40 00 00 00 00 00 |..........@.....|
00000050 00 00 40 00 00 00 00 00 89 00 00 00 00 00 00 00 |..@.............|
00000060 89 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00 |................|
00000070 6a 07 5a 6a 01 58 be 08 00 40 00 48 89 c7 0f 05 |j.Zj.X...@.H....|
00000080 6a 3c 58 31 ff 0f 05 0f 0b |j<X1.....|
00000089
+ wc -c tinyrust
137 tinyrust
$ ./tinyrust
Hello!Licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.