1 //! Reading and writing of the rustc metadata for rlibs and dylibs
6 use rustc_codegen_ssa::METADATA_FILENAME;
7 use rustc_data_structures::memmap::Mmap;
8 use rustc_data_structures::owning_ref::OwningRef;
9 use rustc_data_structures::rustc_erase_owner;
10 use rustc_data_structures::sync::MetadataRef;
11 use rustc_middle::middle::cstore::MetadataLoader;
12 use rustc_middle::ty::TyCtxt;
13 use rustc_target::spec::Target;
15 use crate::backend::WriteMetadata;
17 /// The metadata loader used by cg_clif.
19 /// The metadata is stored in the same format as cg_llvm.
21 /// # Metadata location
25 /// <dd>The metadata can be found in the `lib.rmeta` file inside of the ar archive.</dd>
27 /// <dd>The metadata can be found in the `.rustc` section of the shared library.</dd>
29 pub(crate) struct CraneliftMetadataLoader;
31 fn load_metadata_with(
33 f: impl for<'a> FnOnce(&'a [u8]) -> Result<&'a [u8], String>,
34 ) -> Result<MetadataRef, String> {
35 let file = File::open(path).map_err(|e| format!("{:?}", e))?;
36 let data = unsafe { Mmap::map(file) }.map_err(|e| format!("{:?}", e))?;
37 let metadata = OwningRef::new(data).try_map(f)?;
38 return Ok(rustc_erase_owner!(metadata.map_owner_box()));
41 impl MetadataLoader for CraneliftMetadataLoader {
42 fn get_rlib_metadata(&self, _target: &Target, path: &Path) -> Result<MetadataRef, String> {
43 load_metadata_with(path, |data| {
44 let archive = object::read::archive::ArchiveFile::parse(&*data)
45 .map_err(|e| format!("{:?}", e))?;
47 for entry_result in archive.members() {
48 let entry = entry_result.map_err(|e| format!("{:?}", e))?;
49 if entry.name() == METADATA_FILENAME.as_bytes() {
50 return Ok(entry.data());
54 Err("couldn't find metadata entry".to_string())
58 fn get_dylib_metadata(&self, _target: &Target, path: &Path) -> Result<MetadataRef, String> {
59 use object::{Object, ObjectSection};
61 load_metadata_with(path, |data| {
62 let file = object::File::parse(&data).map_err(|e| format!("parse: {:?}", e))?;
63 file.section_by_name(".rustc")
64 .ok_or("no .rustc section")?
66 .map_err(|e| format!("failed to read .rustc section: {:?}", e))
71 // Adapted from https://github.com/rust-lang/rust/blob/da573206f87b5510de4b0ee1a9c044127e409bd3/src/librustc_codegen_llvm/base.rs#L47-L112
72 pub(crate) fn write_metadata<O: WriteMetadata>(tcx: TyCtxt<'_>, object: &mut O) {
73 use snap::write::FrameEncoder;
76 let metadata = tcx.encode_metadata();
77 let mut compressed = tcx.metadata_encoding_version();
78 FrameEncoder::new(&mut compressed).write_all(&metadata.raw_data).unwrap();
80 object.add_rustc_section(
81 rustc_middle::middle::exported_symbols::metadata_symbol_name(tcx),