Use the object crate for metadata reading

Cargo.lock

@@ -2348,8 +2348,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8d3b63360ec3cb337817c2dbd47ab4a0f170d285d8e5a2064600f3def1402397"
 dependencies = [
  "compiler_builtins",
+ "flate2",
  "rustc-std-workspace-alloc",
  "rustc-std-workspace-core",
+ "wasmparser",
 ]
 
 [[package]]
@@ -3700,6 +3702,7 @@ dependencies = [
  "itertools 0.9.0",
  "jobserver",
  "libc",
+ "object",
  "pathdiff",
  "rustc_apfloat",
  "rustc_ast",
@@ -5618,6 +5621,12 @@ dependencies = [
  "rustc-std-workspace-core",
 ]
 
+[[package]]
+name = "wasmparser"
+version = "0.57.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32fddd575d477c6e9702484139cf9f23dcd554b06d185ed0f56c857dd3a47aa6"
+
 [[package]]
 name = "winapi"
 version = "0.2.8"

compiler/rustc_codegen_cranelift/src/lib.rs

@@ -165,7 +165,7 @@ impl CodegenBackend for CraneliftCodegenBackend {
     }
 
     fn metadata_loader(&self) -> Box<dyn MetadataLoader + Sync> {
-        Box::new(crate::metadata::CraneliftMetadataLoader)
+        Box::new(rustc_codegen_ssa::back::metadata::DefaultMetadataLoader)
     }
 
     fn provide(&self, _providers: &mut Providers) {}

compiler/rustc_codegen_cranelift/src/metadata.rs

@@ -1,73 +1,9 @@
-//! Reading and writing of the rustc metadata for rlibs and dylibs
+//! Writing of the rustc metadata for dylibs
 
-use std::fs::File;
-use std::path::Path;
-
-use rustc_codegen_ssa::METADATA_FILENAME;
-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_middle::middle::cstore::MetadataLoader;
 use rustc_middle::ty::TyCtxt;
-use rustc_target::spec::Target;
 
 use crate::backend::WriteMetadata;
 
-/// The metadata loader used by cg_clif.
-///
-/// The metadata is stored in the same format as cg_llvm.
-///
-/// # 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(crate) struct CraneliftMetadataLoader;
-
-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!("{:?}", e))?;
-    let data = unsafe { Mmap::map(file) }.map_err(|e| format!("{:?}", e))?;
-    let metadata = OwningRef::new(data).try_map(f)?;
-    return Ok(rustc_erase_owner!(metadata.map_owner_box()));
-}
-
-impl MetadataLoader for CraneliftMetadataLoader {
-    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!("{:?}", e))?;
-
-            for entry_result in archive.members() {
-                let entry = entry_result.map_err(|e| format!("{:?}", e))?;
-                if entry.name() == METADATA_FILENAME.as_bytes() {
-                    return Ok(entry.data());
-                }
-            }
-
-            Err("couldn't find metadata entry".to_string())
-        })
-    }
-
-    fn get_dylib_metadata(&self, _target: &Target, path: &Path) -> Result<MetadataRef, String> {
-        use object::{Object, ObjectSection};
-
-        load_metadata_with(path, |data| {
-            let file = object::File::parse(&data).map_err(|e| format!("parse: {:?}", e))?;
-            file.section_by_name(".rustc")
-                .ok_or("no .rustc section")?
-                .data()
-                .map_err(|e| format!("failed to read .rustc section: {:?}", e))
-        })
-    }
-}
-
 // Adapted from https://github.com/rust-lang/rust/blob/da573206f87b5510de4b0ee1a9c044127e409bd3/src/librustc_codegen_llvm/base.rs#L47-L112
 pub(crate) fn write_metadata<O: WriteMetadata>(tcx: TyCtxt<'_>, object: &mut O) {
     use snap::write::FrameEncoder;

compiler/rustc_codegen_llvm/src/base.rs

@@ -18,7 +18,6 @@ use crate::builder::Builder;
 use crate::common;
 use crate::context::CodegenCx;
 use crate::llvm;
-use crate::metadata;
 use crate::value::Value;
 
 use rustc_codegen_ssa::base::maybe_create_entry_wrapper;
@@ -47,6 +46,21 @@ pub fn write_compressed_metadata<'tcx>(
     use snap::write::FrameEncoder;
     use std::io::Write;
 
+    // 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, that's another good question...
+    let section_name = if tcx.sess.target.is_like_osx { "__DATA,.rustc" } else { ".rustc" };
+
     let (metadata_llcx, metadata_llmod) = (&*llvm_module.llcx, llvm_module.llmod());
     let mut compressed = tcx.metadata_encoding_version();
     FrameEncoder::new(&mut compressed).write_all(&metadata.raw_data).unwrap();
@@ -59,7 +73,6 @@ pub fn write_compressed_metadata<'tcx>(
         unsafe { llvm::LLVMAddGlobal(metadata_llmod, common::val_ty(llconst), buf.as_ptr()) };
     unsafe {
         llvm::LLVMSetInitializer(llglobal, llconst);
-        let section_name = metadata::metadata_section_name(&tcx.sess.target);
         let name = SmallCStr::new(section_name);
         llvm::LLVMSetSection(llglobal, name.as_ptr());
 

compiler/rustc_codegen_llvm/src/lib.rs

@@ -69,7 +69,6 @@ pub mod llvm {
 }
 
 mod llvm_util;
-mod metadata;
 mod mono_item;
 mod type_;
 mod type_of;
@@ -250,7 +249,7 @@ impl CodegenBackend for LlvmCodegenBackend {
     }
 
     fn metadata_loader(&self) -> Box<MetadataLoaderDyn> {
-        Box::new(metadata::LlvmMetadataLoader)
+        Box::new(rustc_codegen_ssa::back::metadata::DefaultMetadataLoader)
     }
 
     fn provide(&self, providers: &mut ty::query::Providers) {

compiler/rustc_codegen_ssa/Cargo.toml

@@ -33,3 +33,8 @@ rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_target = { path = "../rustc_target" }
 rustc_session = { path = "../rustc_session" }
+
+[dependencies.object]
+version = "0.22.0"
+default-features = false
+features = ["read_core", "elf", "macho", "pe", "unaligned", "archive"]

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -0,0 +1,65 @@
+//! Reading of the rustc metadata for rlibs and dylibs
+
+use std::fs::File;
+use std::path::Path;
+
+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_middle::middle::cstore::MetadataLoader;
+use rustc_target::spec::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!("{:?}", e))?;
+    let data = unsafe { Mmap::map(file) }.map_err(|e| format!("{:?}", 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!("{:?}", e))?;
+
+            for entry_result in archive.members() {
+                let entry = entry_result.map_err(|e| format!("{:?}", e))?;
+                if entry.name() == METADATA_FILENAME.as_bytes() {
+                    return Ok(entry.data());
+                }
+            }
+
+            Err("couldn't find metadata entry".to_string())
+        })
+    }
+
+    fn get_dylib_metadata(&self, _target: &Target, path: &Path) -> Result<MetadataRef, String> {
+        use object::{Object, ObjectSection};
+
+        load_metadata_with(path, |data| {
+            let file = object::File::parse(&data).map_err(|e| format!("parse: {:?}", e))?;
+            file.section_by_name(".rustc")
+                .ok_or("no .rustc section")?
+                .data()
+                .map_err(|e| format!("failed to read .rustc section: {:?}", e))
+        })
+    }
+}

compiler/rustc_codegen_ssa/src/back/mod.rs

@@ -3,6 +3,7 @@ pub mod command;
 pub mod link;
 pub mod linker;
 pub mod lto;
+pub mod metadata;
 pub mod rpath;
 pub mod symbol_export;
 pub mod write;

src/tools/tidy/src/deps.rs

@@ -42,6 +42,7 @@ const EXCEPTIONS: &[(&str, &str)] = &[
     ("snap", "BSD-3-Clause"),           // rustc
     // FIXME: this dependency violates the documentation comment above:
     ("fortanix-sgx-abi", "MPL-2.0"), // libstd but only for `sgx` target
+    ("wasmparser", "Apache-2.0 WITH LLVM-exception"), // rustc
 ];
 
 const EXCEPTIONS_CRANELIFT: &[(&str, &str)] = &[
@@ -222,6 +223,7 @@ const PERMITTED_DEPENDENCIES: &[&str] = &[
     "vcpkg",
     "version_check",
     "wasi",
+    "wasmparser",
     "winapi",
     "winapi-build",
     "winapi-i686-pc-windows-gnu",