| //! Management of the encoding of LLVM bytecode into rlibs |
| //! |
| //! This module contains the management of encoding LLVM bytecode into rlibs, |
| //! primarily for the usage in LTO situations. Currently the compiler will |
| //! unconditionally encode LLVM-IR into rlibs regardless of what's happening |
| //! elsewhere, so we currently compress the bytecode via deflate to avoid taking |
| //! up too much space on disk. |
| //! |
| //! After compressing the bytecode we then have the rest of the format to |
| //! basically deal with various bugs in various archive implementations. The |
| //! format currently is: |
| //! |
| //! RLIB LLVM-BYTECODE OBJECT LAYOUT |
| //! Version 2 |
| //! Bytes Data |
| //! 0..10 "RUST_OBJECT" encoded in ASCII |
| //! 11..14 format version as little-endian u32 |
| //! 15..19 the length of the module identifier string |
| //! 20..n the module identifier string |
| //! n..n+8 size in bytes of deflate compressed LLVM bitcode as |
| //! little-endian u64 |
| //! n+9.. compressed LLVM bitcode |
| //! ? maybe a byte to make this whole thing even length |
| |
| use std::io::{Read, Write}; |
| use std::ptr; |
| use std::str; |
| |
| use flate2::read::DeflateDecoder; |
| use flate2::write::DeflateEncoder; |
| use flate2::Compression; |
| |
| // This is the "magic number" expected at the beginning of a LLVM bytecode |
| // object in an rlib. |
| pub const RLIB_BYTECODE_OBJECT_MAGIC: &[u8] = b"RUST_OBJECT"; |
| |
| // The version number this compiler will write to bytecode objects in rlibs |
| pub const RLIB_BYTECODE_OBJECT_VERSION: u8 = 2; |
| |
| pub fn encode(identifier: &str, bytecode: &[u8]) -> Vec<u8> { |
| let mut encoded = Vec::new(); |
| |
| // Start off with the magic string |
| encoded.extend_from_slice(RLIB_BYTECODE_OBJECT_MAGIC); |
| |
| // Next up is the version |
| encoded.extend_from_slice(&[RLIB_BYTECODE_OBJECT_VERSION, 0, 0, 0]); |
| |
| // Next is the LLVM module identifier length + contents |
| let identifier_len = identifier.len(); |
| encoded.extend_from_slice(&[ |
| (identifier_len >> 0) as u8, |
| (identifier_len >> 8) as u8, |
| (identifier_len >> 16) as u8, |
| (identifier_len >> 24) as u8, |
| ]); |
| encoded.extend_from_slice(identifier.as_bytes()); |
| |
| // Next is the LLVM module deflate compressed, prefixed with its length. We |
| // don't know its length yet, so fill in 0s |
| let deflated_size_pos = encoded.len(); |
| encoded.extend_from_slice(&[0, 0, 0, 0, 0, 0, 0, 0]); |
| |
| let before = encoded.len(); |
| DeflateEncoder::new(&mut encoded, Compression::fast()).write_all(bytecode).unwrap(); |
| let after = encoded.len(); |
| |
| // Fill in the length we reserved space for before |
| let bytecode_len = (after - before) as u64; |
| encoded[deflated_size_pos + 0] = (bytecode_len >> 0) as u8; |
| encoded[deflated_size_pos + 1] = (bytecode_len >> 8) as u8; |
| encoded[deflated_size_pos + 2] = (bytecode_len >> 16) as u8; |
| encoded[deflated_size_pos + 3] = (bytecode_len >> 24) as u8; |
| encoded[deflated_size_pos + 4] = (bytecode_len >> 32) as u8; |
| encoded[deflated_size_pos + 5] = (bytecode_len >> 40) as u8; |
| encoded[deflated_size_pos + 6] = (bytecode_len >> 48) as u8; |
| encoded[deflated_size_pos + 7] = (bytecode_len >> 56) as u8; |
| |
| // If the number of bytes written to the object so far is odd, add a |
| // padding byte to make it even. This works around a crash bug in LLDB |
| // (see issue #15950) |
| if encoded.len() % 2 == 1 { |
| encoded.push(0); |
| } |
| |
| return encoded; |
| } |
| |
| pub struct DecodedBytecode<'a> { |
| identifier: &'a str, |
| encoded_bytecode: &'a [u8], |
| } |
| |
| impl<'a> DecodedBytecode<'a> { |
| pub fn new(data: &'a [u8]) -> Result<DecodedBytecode<'a>, &'static str> { |
| if !data.starts_with(RLIB_BYTECODE_OBJECT_MAGIC) { |
| return Err("magic bytecode prefix not found"); |
| } |
| let data = &data[RLIB_BYTECODE_OBJECT_MAGIC.len()..]; |
| if !data.starts_with(&[RLIB_BYTECODE_OBJECT_VERSION, 0, 0, 0]) { |
| return Err("wrong version prefix found in bytecode"); |
| } |
| let data = &data[4..]; |
| if data.len() < 4 { |
| return Err("bytecode corrupted"); |
| } |
| let identifier_len = |
| unsafe { u32::from_le(ptr::read_unaligned(data.as_ptr() as *const u32)) as usize }; |
| let data = &data[4..]; |
| if data.len() < identifier_len { |
| return Err("bytecode corrupted"); |
| } |
| let identifier = match str::from_utf8(&data[..identifier_len]) { |
| Ok(s) => s, |
| Err(_) => return Err("bytecode corrupted"), |
| }; |
| let data = &data[identifier_len..]; |
| if data.len() < 8 { |
| return Err("bytecode corrupted"); |
| } |
| let bytecode_len = |
| unsafe { u64::from_le(ptr::read_unaligned(data.as_ptr() as *const u64)) as usize }; |
| let data = &data[8..]; |
| if data.len() < bytecode_len { |
| return Err("bytecode corrupted"); |
| } |
| let encoded_bytecode = &data[..bytecode_len]; |
| |
| Ok(DecodedBytecode { identifier, encoded_bytecode }) |
| } |
| |
| pub fn bytecode(&self) -> Vec<u8> { |
| let mut data = Vec::new(); |
| DeflateDecoder::new(self.encoded_bytecode).read_to_end(&mut data).unwrap(); |
| return data; |
| } |
| |
| pub fn identifier(&self) -> &'a str { |
| self.identifier |
| } |
| } |