| //! Reading of the rustc metadata for rlibs and dylibs |
| |
| use std::fs::File; |
| use std::io::Write; |
| use std::path::Path; |
| |
| use object::write::{self, StandardSegment, Symbol, SymbolSection}; |
| use object::{ |
| elf, pe, Architecture, BinaryFormat, Endianness, FileFlags, Object, ObjectSection, |
| SectionFlags, SectionKind, SymbolFlags, SymbolKind, SymbolScope, |
| }; |
| |
| use snap::write::FrameEncoder; |
| |
| use rustc_data_structures::memmap::Mmap; |
| use rustc_data_structures::owning_ref::OwningRef; |
| use rustc_data_structures::rustc_erase_owner; |
| use rustc_data_structures::sync::MetadataRef; |
| use rustc_metadata::EncodedMetadata; |
| use rustc_session::cstore::MetadataLoader; |
| use rustc_session::Session; |
| use rustc_target::abi::Endian; |
| use rustc_target::spec::{RelocModel, Target}; |
| |
| use crate::METADATA_FILENAME; |
| |
| /// The default metadata loader. This is used by cg_llvm and cg_clif. |
| /// |
| /// # Metadata location |
| /// |
| /// <dl> |
| /// <dt>rlib</dt> |
| /// <dd>The metadata can be found in the `lib.rmeta` file inside of the ar archive.</dd> |
| /// <dt>dylib</dt> |
| /// <dd>The metadata can be found in the `.rustc` section of the shared library.</dd> |
| /// </dl> |
| pub struct DefaultMetadataLoader; |
| |
| fn load_metadata_with( |
| path: &Path, |
| f: impl for<'a> FnOnce(&'a [u8]) -> Result<&'a [u8], String>, |
| ) -> Result<MetadataRef, String> { |
| let file = |
| File::open(path).map_err(|e| format!("failed to open file '{}': {}", path.display(), e))?; |
| let data = unsafe { Mmap::map(file) } |
| .map_err(|e| format!("failed to mmap file '{}': {}", path.display(), e))?; |
| let metadata = OwningRef::new(data).try_map(f)?; |
| return Ok(rustc_erase_owner!(metadata.map_owner_box())); |
| } |
| |
| impl MetadataLoader for DefaultMetadataLoader { |
| fn get_rlib_metadata(&self, _target: &Target, path: &Path) -> Result<MetadataRef, String> { |
| load_metadata_with(path, |data| { |
| let archive = object::read::archive::ArchiveFile::parse(&*data) |
| .map_err(|e| format!("failed to parse rlib '{}': {}", path.display(), e))?; |
| |
| for entry_result in archive.members() { |
| let entry = entry_result |
| .map_err(|e| format!("failed to parse rlib '{}': {}", path.display(), e))?; |
| if entry.name() == METADATA_FILENAME.as_bytes() { |
| let data = entry |
| .data(data) |
| .map_err(|e| format!("failed to parse rlib '{}': {}", path.display(), e))?; |
| return search_for_metadata(path, data, ".rmeta"); |
| } |
| } |
| |
| Err(format!("metadata not found in rlib '{}'", path.display())) |
| }) |
| } |
| |
| fn get_dylib_metadata(&self, _target: &Target, path: &Path) -> Result<MetadataRef, String> { |
| load_metadata_with(path, |data| search_for_metadata(path, data, ".rustc")) |
| } |
| } |
| |
| fn search_for_metadata<'a>( |
| path: &Path, |
| bytes: &'a [u8], |
| section: &str, |
| ) -> Result<&'a [u8], String> { |
| let Ok(file) = object::File::parse(bytes) else { |
| // The parse above could fail for odd reasons like corruption, but for |
| // now we just interpret it as this target doesn't support metadata |
| // emission in object files so the entire byte slice itself is probably |
| // a metadata file. Ideally though if necessary we could at least check |
| // the prefix of bytes to see if it's an actual metadata object and if |
| // not forward the error along here. |
| return Ok(bytes); |
| }; |
| file.section_by_name(section) |
| .ok_or_else(|| format!("no `{}` section in '{}'", section, path.display()))? |
| .data() |
| .map_err(|e| format!("failed to read {} section in '{}': {}", section, path.display(), e)) |
| } |
| |
| pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static>> { |
| let endianness = match sess.target.options.endian { |
| Endian::Little => Endianness::Little, |
| Endian::Big => Endianness::Big, |
| }; |
| let architecture = match &sess.target.arch[..] { |
| "arm" => Architecture::Arm, |
| "aarch64" => Architecture::Aarch64, |
| "x86" => Architecture::I386, |
| "s390x" => Architecture::S390x, |
| "mips" => Architecture::Mips, |
| "mips64" => Architecture::Mips64, |
| "x86_64" => { |
| if sess.target.pointer_width == 32 { |
| Architecture::X86_64_X32 |
| } else { |
| Architecture::X86_64 |
| } |
| } |
| "powerpc" => Architecture::PowerPc, |
| "powerpc64" => Architecture::PowerPc64, |
| "riscv32" => Architecture::Riscv32, |
| "riscv64" => Architecture::Riscv64, |
| "sparc64" => Architecture::Sparc64, |
| // Unsupported architecture. |
| _ => return None, |
| }; |
| let binary_format = if sess.target.is_like_osx { |
| BinaryFormat::MachO |
| } else if sess.target.is_like_windows { |
| BinaryFormat::Coff |
| } else { |
| BinaryFormat::Elf |
| }; |
| |
| let mut file = write::Object::new(binary_format, architecture, endianness); |
| let e_flags = match architecture { |
| Architecture::Mips => { |
| let arch = match sess.target.options.cpu.as_ref() { |
| "mips1" => elf::EF_MIPS_ARCH_1, |
| "mips2" => elf::EF_MIPS_ARCH_2, |
| "mips3" => elf::EF_MIPS_ARCH_3, |
| "mips4" => elf::EF_MIPS_ARCH_4, |
| "mips5" => elf::EF_MIPS_ARCH_5, |
| s if s.contains("r6") => elf::EF_MIPS_ARCH_32R6, |
| _ => elf::EF_MIPS_ARCH_32R2, |
| }; |
| // The only ABI LLVM supports for 32-bit MIPS CPUs is o32. |
| let mut e_flags = elf::EF_MIPS_CPIC | elf::EF_MIPS_ABI_O32 | arch; |
| if sess.target.options.relocation_model != RelocModel::Static { |
| e_flags |= elf::EF_MIPS_PIC; |
| } |
| if sess.target.options.cpu.contains("r6") { |
| e_flags |= elf::EF_MIPS_NAN2008; |
| } |
| e_flags |
| } |
| Architecture::Mips64 => { |
| // copied from `mips64el-linux-gnuabi64-gcc foo.c -c` |
| let e_flags = elf::EF_MIPS_CPIC |
| | elf::EF_MIPS_PIC |
| | if sess.target.options.cpu.contains("r6") { |
| elf::EF_MIPS_ARCH_64R6 | elf::EF_MIPS_NAN2008 |
| } else { |
| elf::EF_MIPS_ARCH_64R2 |
| }; |
| e_flags |
| } |
| Architecture::Riscv64 if sess.target.options.features.contains("+d") => { |
| // copied from `riscv64-linux-gnu-gcc foo.c -c`, note though |
| // that the `+d` target feature represents whether the double |
| // float abi is enabled. |
| let e_flags = elf::EF_RISCV_RVC | elf::EF_RISCV_FLOAT_ABI_DOUBLE; |
| e_flags |
| } |
| _ => 0, |
| }; |
| // adapted from LLVM's `MCELFObjectTargetWriter::getOSABI` |
| let os_abi = match sess.target.options.os.as_ref() { |
| "hermit" => elf::ELFOSABI_STANDALONE, |
| "freebsd" => elf::ELFOSABI_FREEBSD, |
| "solaris" => elf::ELFOSABI_SOLARIS, |
| _ => elf::ELFOSABI_NONE, |
| }; |
| let abi_version = 0; |
| file.flags = FileFlags::Elf { os_abi, abi_version, e_flags }; |
| Some(file) |
| } |
| |
| pub enum MetadataPosition { |
| First, |
| Last, |
| } |
| |
| // For rlibs we "pack" rustc metadata into a dummy object file. When rustc |
| // creates a dylib crate type it will pass `--whole-archive` (or the |
| // platform equivalent) to include all object files from an rlib into the |
| // final dylib itself. This causes linkers to iterate and try to include all |
| // files located in an archive, so if metadata is stored in an archive then |
| // it needs to be of a form that the linker will be able to process. |
| // |
| // Note, though, that we don't actually want this metadata to show up in any |
| // final output of the compiler. Instead this is purely for rustc's own |
| // metadata tracking purposes. |
| // |
| // With the above in mind, each "flavor" of object format gets special |
| // handling here depending on the target: |
| // |
| // * MachO - macos-like targets will insert the metadata into a section that |
| // is sort of fake dwarf debug info. Inspecting the source of the macos |
| // linker this causes these sections to be skipped automatically because |
| // it's not in an allowlist of otherwise well known dwarf section names to |
| // go into the final artifact. |
| // |
| // * WebAssembly - we actually don't have any container format for this |
| // target. WebAssembly doesn't support the `dylib` crate type anyway so |
| // there's no need for us to support this at this time. Consequently the |
| // metadata bytes are simply stored as-is into an rlib. |
| // |
| // * COFF - Windows-like targets create an object with a section that has |
| // the `IMAGE_SCN_LNK_REMOVE` flag set which ensures that if the linker |
| // ever sees the section it doesn't process it and it's removed. |
| // |
| // * ELF - All other targets are similar to Windows in that there's a |
| // `SHF_EXCLUDE` flag we can set on sections in an object file to get |
| // automatically removed from the final output. |
| pub fn create_rmeta_file(sess: &Session, metadata: &[u8]) -> (Vec<u8>, MetadataPosition) { |
| let Some(mut file) = create_object_file(sess) else { |
| // This is used to handle all "other" targets. This includes targets |
| // in two categories: |
| // |
| // * Some targets don't have support in the `object` crate just yet |
| // to write an object file. These targets are likely to get filled |
| // out over time. |
| // |
| // * Targets like WebAssembly don't support dylibs, so the purpose |
| // of putting metadata in object files, to support linking rlibs |
| // into dylibs, is moot. |
| // |
| // In both of these cases it means that linking into dylibs will |
| // not be supported by rustc. This doesn't matter for targets like |
| // WebAssembly and for targets not supported by the `object` crate |
| // yet it means that work will need to be done in the `object` crate |
| // to add a case above. |
| return (metadata.to_vec(), MetadataPosition::Last); |
| }; |
| let section = file.add_section( |
| file.segment_name(StandardSegment::Debug).to_vec(), |
| b".rmeta".to_vec(), |
| SectionKind::Debug, |
| ); |
| match file.format() { |
| BinaryFormat::Coff => { |
| file.section_mut(section).flags = |
| SectionFlags::Coff { characteristics: pe::IMAGE_SCN_LNK_REMOVE }; |
| } |
| BinaryFormat::Elf => { |
| file.section_mut(section).flags = |
| SectionFlags::Elf { sh_flags: elf::SHF_EXCLUDE as u64 }; |
| } |
| _ => {} |
| }; |
| file.append_section_data(section, metadata, 1); |
| (file.write().unwrap(), MetadataPosition::First) |
| } |
| |
| // Historical note: |
| // |
| // When using link.exe it was seen that the section name `.note.rustc` |
| // was getting shortened to `.note.ru`, and according to the PE and COFF |
| // specification: |
| // |
| // > Executable images do not use a string table and do not support |
| // > section names longer than 8 characters |
| // |
| // https://docs.microsoft.com/en-us/windows/win32/debug/pe-format |
| // |
| // As a result, we choose a slightly shorter name! As to why |
| // `.note.rustc` works on MinGW, see |
| // https://github.com/llvm/llvm-project/blob/llvmorg-12.0.0/lld/COFF/Writer.cpp#L1190-L1197 |
| pub fn create_compressed_metadata_file( |
| sess: &Session, |
| metadata: &EncodedMetadata, |
| symbol_name: &str, |
| ) -> Vec<u8> { |
| let mut compressed = rustc_metadata::METADATA_HEADER.to_vec(); |
| FrameEncoder::new(&mut compressed).write_all(metadata.raw_data()).unwrap(); |
| let Some(mut file) = create_object_file(sess) else { |
| return compressed.to_vec(); |
| }; |
| let section = file.add_section( |
| file.segment_name(StandardSegment::Data).to_vec(), |
| b".rustc".to_vec(), |
| SectionKind::ReadOnlyData, |
| ); |
| match file.format() { |
| BinaryFormat::Elf => { |
| // Explicitly set no flags to avoid SHF_ALLOC default for data section. |
| file.section_mut(section).flags = SectionFlags::Elf { sh_flags: 0 }; |
| } |
| _ => {} |
| }; |
| let offset = file.append_section_data(section, &compressed, 1); |
| |
| // For MachO and probably PE this is necessary to prevent the linker from throwing away the |
| // .rustc section. For ELF this isn't necessary, but it also doesn't harm. |
| file.add_symbol(Symbol { |
| name: symbol_name.as_bytes().to_vec(), |
| value: offset, |
| size: compressed.len() as u64, |
| kind: SymbolKind::Data, |
| scope: SymbolScope::Dynamic, |
| weak: false, |
| section: SymbolSection::Section(section), |
| flags: SymbolFlags::None, |
| }); |
| |
| file.write().unwrap() |
| } |
