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