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Diffstat (limited to 'src/librustc_trans/back/bytecode.rs')
| -rw-r--r-- | src/librustc_trans/back/bytecode.rs | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/src/librustc_trans/back/bytecode.rs b/src/librustc_trans/back/bytecode.rs new file mode 100644 index 00000000000..55c96322a95 --- /dev/null +++ b/src/librustc_trans/back/bytecode.rs @@ -0,0 +1,160 @@ +// Copyright 2017 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or +// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license +// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +//! 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::Compression; +use flate2::read::DeflateDecoder; +use flate2::write::DeflateEncoder; + +// This is the "magic number" expected at the beginning of a LLVM bytecode +// object in an rlib. +pub const RLIB_BYTECODE_OBJECT_MAGIC: &'static [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 const RLIB_BYTECODE_EXTENSION: &str = "bytecode.encoded"; + +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>, String> { + if !data.starts_with(RLIB_BYTECODE_OBJECT_MAGIC) { + return Err(format!("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(format!("wrong version prefix found in bytecode")) + } + let data = &data[4..]; + if data.len() < 4 { + return Err(format!("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(format!("bytecode corrupted")) + } + let identifier = match str::from_utf8(&data[..identifier_len]) { + Ok(s) => s, + Err(_) => return Err(format!("bytecode corrupted")) + }; + let data = &data[identifier_len..]; + if data.len() < 8 { + return Err(format!("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(format!("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 + } +} |