faerie

Emit some object files, at your leisure:

let name = "test.o";
let file = File::create(Path::new(name))?;
let mut obj = ArtifactBuilder::new(Target::X86_64)
    .name(name)
    .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 { global: false }),
        ("main",     Decl::Function { global: true }),
        ("str.1",    Decl::CString { global: false }),
        ("DEADBEEF", Decl::DataImport),
        ("printf",   Decl::FunctionImport),
    ].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 which object file we desire
obj.write::<Elf>(file)?;

Will emit an object file like this:

:sunglasses: