faerie 
.
Emit some object files, at your leisure:
let name = "test.o";
let file = File::create(Path::new(name))?;
let mut obj = ArtifactBuilder::new(triple!("x86_64-unknown-unknown-unknown-elf"))
.name(name.to_owned())
.finish();
// first we declare our symbolic references;
// it is a runtime error to define a symbol _without_ declaring it first
obj.declarations(
[
("deadbeef", Decl::function().into()),
("main", Decl::function().global().into()),
("str.1", Decl::cstring().into()),
("DEADBEEF", Decl::data_import().into()),
("printf", Decl::function_import().into()),
].iter().cloned()
)?;
// we now define our local functions and data
// 0000000000000000 <deadbeef>:
// 0: 55 push %rbp
// 1: 48 89 e5 mov %rsp,%rbp
// 4: 48 8b 05 00 00 00 00 mov 0x0(%rip),%rax # b <deadbeef+0xb>
// 7: R_X86_64_GOTPCREL DEADBEEF-0x4
// b: 8b 08 mov (%rax),%ecx
// d: 83 c1 01 add $0x1,%ecx
// 10: 89 c8 mov %ecx,%eax
// 12: 5d pop %rbp
// 13: c3 retq
obj.define("deadbeef",
vec![0x55,
0x48, 0x89, 0xe5,
0x48, 0x8b, 0x05, 0x00, 0x00, 0x00, 0x00,
0x8b, 0x08,
0x83, 0xc1, 0x01,
0x89, 0xc8,
0x5d,
0xc3])?;
// main:
// 55 push %rbp
// 48 89 e5 mov %rsp,%rbp
// b8 00 00 00 00 mov $0x0,%eax
// e8 00 00 00 00 callq 0x0 <deadbeef>
// 89 c6 mov %eax,%esi
// 48 8d 3d 00 00 00 00 lea 0x0(%rip),%rdi # will be: deadbeef: 0x%x\n
// b8 00 00 00 00 mov $0x0,%eax
// e8 00 00 00 00 callq 0x3f <main+33> # printf
// b8 00 00 00 00 mov $0x0,%eax
// 5d pop %rbp
// c3 retq
obj.define("main",
vec![0x55,
0x48, 0x89, 0xe5,
0xb8, 0x00, 0x00, 0x00, 0x00,
0xe8, 0x00, 0x00, 0x00, 0x00,
0x89, 0xc6,
0x48, 0x8d, 0x3d, 0x00, 0x00, 0x00, 0x00,
0xb8, 0x00, 0x00, 0x00, 0x00,
0xe8, 0x00, 0x00, 0x00, 0x00,
0xb8, 0x00, 0x00, 0x00, 0x00,
0x5d,
0xc3])?;
obj.define("str.1", b"deadbeef: 0x%x\n\0".to_vec())?;
// Next, we declare our relocations,
// which are _always_ relative to the `from` symbol
obj.link(Link { from: "main", to: "str.1", at: 19 })?;
obj.link(Link { from: "main", to: "printf", at: 29 })?;
obj.link(Link { from: "main", to: "deadbeef", at: 10 })?;
obj.link(Link { from: "deadbeef", to: "DEADBEEF", at: 7 })?;
// Finally, we write the object file
obj.write(file)?;Will emit an object file like this:
ELF REL X86_64-little-endian @ 0x0: e_phoff: 0x0 e_shoff: 0x2a2 e_flags: 0x0 e_ehsize: 64 e_phentsize: 56 e_phnum: 0 e_shentsize: 64 e_shnum: 9 e_shstrndx: 1 SectionHeaders(9): Idx Name Type Flags Offset Addr Size Link Entsize Align 0 SHT_NULL 0x0 0x0 0x0 0x0 0x0 1 .strtab SHT_STRTAB 0x8c 0x0 0xc6 0x0 0x1 2 .symtab SHT_SYMTAB 0x152 0x0 0xf0 .strtab(1) 0x18 0x8 3 .rodata.str.1 SHT_PROGBITS ALLOC MERGE STRINGS 0x40 0x0 0x10 0x1 0x1 4 .text.deadbeef SHT_PROGBITS ALLOC EXECINSTR 0x50 0x0 0x14 0x0 0x10 5 .text.main SHT_PROGBITS ALLOC EXECINSTR 0x64 0x0 0x28 0x0 0x10 6 .reloc.main SHT_RELA 0x242 0x0 0x48 .symtab(2) 0x18 0x8 7 .reloc.deadbeef SHT_RELA 0x28a 0x0 0x18 .symtab(2) 0x18 0x8 8 .note.GNU-stack SHT_PROGBITS 0x0 0x0 0x0 0x0 0x1 Syms(10): Addr Bind Type Symbol Size Section Other 0 LOCAL NOTYPE 0x0 0x0 0 LOCAL FILE test.o 0x0 ABS 0x0 0 LOCAL SECTION 0x0 .rodata.str.1(3) 0x0 0 LOCAL SECTION 0x0 .text.deadbeef(4) 0x0 0 LOCAL SECTION 0x0 .text.main(5) 0x0 0 LOCAL OBJECT str.1 0x10 .rodata.str.1(3) 0x0 0 LOCAL FUNC deadbeef 0x14 .text.deadbeef(4) 0x0 0 GLOBAL FUNC main 0x28 .text.main(5) 0x0 0 GLOBAL NOTYPE DEADBEEF 0x0 0x0 0 GLOBAL NOTYPE printf 0x0 0x0 Shdr Relocations(4): .text.main(3) 13 X86_64_PC32 .rodata.str.1 1d X86_64_PLT32 printf+-4 a X86_64_PLT32 .text.deadbeef+-4 .text.deadbeef(1) 7 X86_64_GOTPCREL DEADBEEF+-4
π