.gitignore

.gdb_history
payload
payload.o
payload.bin
packed
packer

Makefile

all: payload packed

diff: packed
	bash -c 'diff -u <(objdump -d --adjust-vma 0x400580 payload.o) \
	                 <(objdump -D -j .rodata --start 0x400580 packed); exit 0'

packed: packed.c
	cc $^ -o $@

packed.c: payload.bin packer
	./packer $< >$@

packer: packer.rs
	rustc $^

payload.bin: payload.o
	objcopy -O binary $^ $@

payload.o: payload.s
	as $^ -o $@

payload: payload.o
	ld -emain $^ -o $@

clean:
	rm -rf *.o *.bin payload packer packed packed.c

packed.c

const double main[] = {
	-1.2882297911452467e-231,
	6.8056493973162633e38,
	2.6960150007992882e43,
	-2.4983353911957602e-127,
	1.3771508940552131e-307,
	2.7327264832829496e-71,
	-7.6918209102389605e-293,
	3.1317446676317955e-300,
	-6.1898042705411802e37,
	-5.1199164284928003e13,
	-2.494354501505855e35,
	-1.6955191902826783e-231,
	-1.3617708398331807e57,
	-4.469585001523332e95,
	-1.6444313123558302e-256,
	-8.815396944887123e4,
	-2.1580062755299081e52,
	-5.637139215118955e8,
	-2.4983353906949675e-127,
};

packer.rs

use std::io::{File, IoError, IoErrorKind, println};
use std::path::Path;

fn main() {
  let mut file = File::open(&Path::new(&std::os::args()[1]));
  println("const double main[] = {");
  loop {
    match file.read_le_f64() {
      Ok(val) =>
        /* 53 bits in mantissa / log2(10) = log10(precision) ≈ 15.95 */
        println!("\t{},", std::f64::to_str_exp_digits(val, 16, false)),
      Err(IoError { kind: IoErrorKind::EndOfFile, .. }) =>
        break,
      Err(error) =>
        panic!("{}", error)
    }
  }
  println("};");
}

payload.s

.text
.globl main
.type main, %function
main:
	# copy to writable memory
	movq	$((.msgpad - .msgstart) / 8), %rcx
	nop
	leaq	.msgstart(%rip), %rsi
	movq	%rsp, %rdi
	subq	%rcx, %rsp
	pushq	%rdi
	rep movsq

	# decode
	movq    $0xa5a5a5a5a5a5a5a5, %rax
	movq	$(.msgpad - .msgstart), %rcx
	movq	(%rsp), %rdi
0:
	xorq	%rax, (%rdi)
	addq	$8, %rdi
	nop
	subq	$8, %rcx
	jnz	0b

	# print
	movq	$1, %rax
	nop
	nop
	movq	$0, %rdi
	popq	%rsi
	movq	$(.msgend - .msgstart), %rdx
	syscall

	# exit
	movq	$60, %rax
	syscall

	.align 8
.msgstart:
	.byte 0xd7, 0xc8, 0x9f, 0x85, 0xc6, 0xc4, 0xcb, 0xcb, 0xca
	.byte 0xd1, 0x85, 0xd7, 0xc0, 0xc8, 0xca, 0xd3, 0xc0, 0x85
	.byte 0x82, 0x8a, 0xc1, 0xc0, 0xd3, 0x8a, 0xd1, 0xd1, 0xdc
	.byte 0x82, 0x9f, 0x85, 0xf5, 0xc0, 0xa5, /* nop */ 0xd7, 0xc8, 0xcc, 0xd6
	.byte 0xd6, 0xcc, 0xca, 0xcb, 0x85, 0xc1, 0xc0, 0xcb, 0xcc
	.byte 0xc0, 0xc1, 0xaf
.msgend:
	# padding
	.align 8, 0xa5
.msgpad: