Auto merge of #83640 - bjorn3:shared_metadata_reader, r=nagisa

Use the object crate for metadata reading

This allows sharing the metadata reader between cg_llvm, cg_clif and other codegen backends.

This is not currently useful for rlib reading with cg_spirv ([rust-gpu](https://github.com/EmbarkStudios/rust-gpu/)) as it uses tar rather than ar as .rlib format, but it is useful for dylib reading required for loading proc macros. (cc `@eddyb)`

The object crate is already trusted as dependency of libstd through backtrace. As far as I know it supports reading all object file formats used by targets for which we support rust dylibs with crate metadata, but I am not certain. If this happens to not be the case, I could keep using LLVM for reading dylib metadata.

Marked as WIP for a perf run and as it is based on #83637.

1 files changed, 1 insertions, 13 deletions

diff --git a/src/test/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs b/src/test/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs
index 684e9760cc6..a9e99d3c10e 100644
--- a/src/test/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs
+++ b/src/test/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs
@@ -28,23 +28,11 @@ use rustc_target::spec::Target;
 use std::any::Any;
 use std::path::Path;
 
-pub struct NoLlvmMetadataLoader;
-
-impl MetadataLoader for NoLlvmMetadataLoader {
-    fn get_rlib_metadata(&self, _: &Target, filename: &Path) -> Result<MetadataRef, String> {
-        unreachable!("some_crate.rs shouldn't depend on any external crates");
-    }
-
-    fn get_dylib_metadata(&self, target: &Target, filename: &Path) -> Result<MetadataRef, String> {
-        unreachable!("some_crate.rs shouldn't depend on any external crates");
-    }
-}
-
 struct TheBackend;
 
 impl CodegenBackend for TheBackend {
     fn metadata_loader(&self) -> Box<MetadataLoaderDyn> {
-        Box::new(NoLlvmMetadataLoader)
+        Box::new(rustc_codegen_ssa::back::metadata::DefaultMetadataLoader)
     }
 
     fn provide(&self, providers: &mut Providers) {}