From 267d55d44acf6bb2821de39d4f868650ff0a9c7b Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Mon, 29 Mar 2021 11:39:13 +0200
Subject: [PATCH 1/8] Use the object crate for metadata reading

---
 Cargo.lock                                    |  9 ++
 compiler/rustc_codegen_cranelift/src/lib.rs   |  2 +-
 .../rustc_codegen_cranelift/src/metadata.rs   | 66 +-------------
 compiler/rustc_codegen_llvm/src/lib.rs        |  2 +-
 compiler/rustc_codegen_llvm/src/metadata.rs   | 89 -------------------
 compiler/rustc_codegen_ssa/Cargo.toml         |  1 +
 .../rustc_codegen_ssa/src/back/metadata.rs    | 65 ++++++++++++++
 compiler/rustc_codegen_ssa/src/back/mod.rs    |  1 +
 8 files changed, 79 insertions(+), 156 deletions(-)
 create mode 100644 compiler/rustc_codegen_ssa/src/back/metadata.rs

diff --git a/Cargo.lock b/Cargo.lock
index 77b917448e950..dc688e3a513cc 100644
--- a/Cargo.lock
+++ b/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"
diff --git a/compiler/rustc_codegen_cranelift/src/lib.rs b/compiler/rustc_codegen_cranelift/src/lib.rs
index 32f403957025a..1ade7c77d123a 100644
--- a/compiler/rustc_codegen_cranelift/src/lib.rs
+++ b/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) {}
diff --git a/compiler/rustc_codegen_cranelift/src/metadata.rs b/compiler/rustc_codegen_cranelift/src/metadata.rs
index 882232fde09d2..ab238244d68d5 100644
--- a/compiler/rustc_codegen_cranelift/src/metadata.rs
+++ b/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;
diff --git a/compiler/rustc_codegen_llvm/src/lib.rs b/compiler/rustc_codegen_llvm/src/lib.rs
index 5ca4b226c38fb..8f95afc1b9181 100644
--- a/compiler/rustc_codegen_llvm/src/lib.rs
+++ b/compiler/rustc_codegen_llvm/src/lib.rs
@@ -250,7 +250,7 @@ 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) {
diff --git a/compiler/rustc_codegen_llvm/src/metadata.rs b/compiler/rustc_codegen_llvm/src/metadata.rs
index decc1e1f70007..4bad93a75674b 100644
--- a/compiler/rustc_codegen_llvm/src/metadata.rs
+++ b/compiler/rustc_codegen_llvm/src/metadata.rs
@@ -1,94 +1,9 @@
-use crate::llvm;
-use crate::llvm::archive_ro::ArchiveRO;
-use crate::llvm::{mk_section_iter, False, ObjectFile};
-use rustc_middle::middle::cstore::MetadataLoader;
 use rustc_target::spec::Target;
 
-use rustc_codegen_ssa::METADATA_FILENAME;
-use rustc_data_structures::owning_ref::OwningRef;
-use rustc_data_structures::rustc_erase_owner;
-use tracing::debug;
-
 use rustc_fs_util::path_to_c_string;
 use std::path::Path;
 use std::slice;
 
-pub use rustc_data_structures::sync::MetadataRef;
-
-pub struct LlvmMetadataLoader;
-
-impl MetadataLoader for LlvmMetadataLoader {
-    fn get_rlib_metadata(&self, _: &Target, filename: &Path) -> Result<MetadataRef, String> {
-        // Use ArchiveRO for speed here, it's backed by LLVM and uses mmap
-        // internally to read the file. We also avoid even using a memcpy by
-        // just keeping the archive along while the metadata is in use.
-        let archive =
-            ArchiveRO::open(filename).map(|ar| OwningRef::new(Box::new(ar))).map_err(|e| {
-                debug!("llvm didn't like `{}`: {}", filename.display(), e);
-                format!("failed to read rlib metadata in '{}': {}", filename.display(), e)
-            })?;
-        let buf: OwningRef<_, [u8]> = archive.try_map(|ar| {
-            ar.iter()
-                .filter_map(|s| s.ok())
-                .find(|sect| sect.name() == Some(METADATA_FILENAME))
-                .map(|s| s.data())
-                .ok_or_else(|| {
-                    debug!("didn't find '{}' in the archive", METADATA_FILENAME);
-                    format!("failed to read rlib metadata: '{}'", filename.display())
-                })
-        })?;
-        Ok(rustc_erase_owner!(buf))
-    }
-
-    fn get_dylib_metadata(&self, target: &Target, filename: &Path) -> Result<MetadataRef, String> {
-        unsafe {
-            let buf = path_to_c_string(filename);
-            let mb = llvm::LLVMRustCreateMemoryBufferWithContentsOfFile(buf.as_ptr())
-                .ok_or_else(|| format!("error reading library: '{}'", filename.display()))?;
-            let of =
-                ObjectFile::new(mb).map(|of| OwningRef::new(Box::new(of))).ok_or_else(|| {
-                    format!("provided path not an object file: '{}'", filename.display())
-                })?;
-            let buf = of.try_map(|of| search_meta_section(of, target, filename))?;
-            Ok(rustc_erase_owner!(buf))
-        }
-    }
-}
-
-fn search_meta_section<'a>(
-    of: &'a ObjectFile,
-    target: &Target,
-    filename: &Path,
-) -> Result<&'a [u8], String> {
-    unsafe {
-        let si = mk_section_iter(of.llof);
-        while llvm::LLVMIsSectionIteratorAtEnd(of.llof, si.llsi) == False {
-            let mut name_buf = None;
-            let name_len = llvm::LLVMRustGetSectionName(si.llsi, &mut name_buf);
-            let name = name_buf.map_or_else(
-                String::new, // We got a null ptr, ignore `name_len`.
-                |buf| {
-                    String::from_utf8(
-                        slice::from_raw_parts(buf.as_ptr() as *const u8, name_len as usize)
-                            .to_vec(),
-                    )
-                    .unwrap()
-                },
-            );
-            debug!("get_metadata_section: name {}", name);
-            if read_metadata_section_name(target) == name {
-                let cbuf = llvm::LLVMGetSectionContents(si.llsi);
-                let csz = llvm::LLVMGetSectionSize(si.llsi) as usize;
-                // The buffer is valid while the object file is around
-                let buf: &'a [u8] = slice::from_raw_parts(cbuf as *const u8, csz);
-                return Ok(buf);
-            }
-            llvm::LLVMMoveToNextSection(si.llsi);
-        }
-    }
-    Err(format!("metadata not found: '{}'", filename.display()))
-}
-
 pub fn metadata_section_name(target: &Target) -> &'static str {
     // Historical note:
     //
@@ -106,7 +21,3 @@ pub fn metadata_section_name(target: &Target) -> &'static str {
 
     if target.is_like_osx { "__DATA,.rustc" } else { ".rustc" }
 }
-
-fn read_metadata_section_name(_target: &Target) -> &'static str {
-    ".rustc"
-}
diff --git a/compiler/rustc_codegen_ssa/Cargo.toml b/compiler/rustc_codegen_ssa/Cargo.toml
index 7a3d715df6dcd..d7d91d09cfa9f 100644
--- a/compiler/rustc_codegen_ssa/Cargo.toml
+++ b/compiler/rustc_codegen_ssa/Cargo.toml
@@ -16,6 +16,7 @@ libc = "0.2.50"
 jobserver = "0.1.22"
 tempfile = "3.2"
 pathdiff = "0.2.0"
+object = "0.22.0"
 
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_ast = { path = "../rustc_ast" }
diff --git a/compiler/rustc_codegen_ssa/src/back/metadata.rs b/compiler/rustc_codegen_ssa/src/back/metadata.rs
new file mode 100644
index 0000000000000..096098fb260c7
--- /dev/null
+++ b/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))
+        })
+    }
+}
diff --git a/compiler/rustc_codegen_ssa/src/back/mod.rs b/compiler/rustc_codegen_ssa/src/back/mod.rs
index 20ca503d43f45..d11ed54eb209f 100644
--- a/compiler/rustc_codegen_ssa/src/back/mod.rs
+++ b/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;

From f5d388302b045f60a417b906f80c00d46db99ee5 Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Mon, 29 Mar 2021 13:02:59 +0200
Subject: [PATCH 2/8] Remove cg_llvm::metadata module

---
 compiler/rustc_codegen_llvm/src/base.rs     | 17 +++++++++++++--
 compiler/rustc_codegen_llvm/src/lib.rs      |  1 -
 compiler/rustc_codegen_llvm/src/metadata.rs | 23 ---------------------
 3 files changed, 15 insertions(+), 26 deletions(-)
 delete mode 100644 compiler/rustc_codegen_llvm/src/metadata.rs

diff --git a/compiler/rustc_codegen_llvm/src/base.rs b/compiler/rustc_codegen_llvm/src/base.rs
index 6f6c649bb0b18..aeb0561c08620 100644
--- a/compiler/rustc_codegen_llvm/src/base.rs
+++ b/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());
 
diff --git a/compiler/rustc_codegen_llvm/src/lib.rs b/compiler/rustc_codegen_llvm/src/lib.rs
index 8f95afc1b9181..4f8ea50acaabc 100644
--- a/compiler/rustc_codegen_llvm/src/lib.rs
+++ b/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;
diff --git a/compiler/rustc_codegen_llvm/src/metadata.rs b/compiler/rustc_codegen_llvm/src/metadata.rs
deleted file mode 100644
index 4bad93a75674b..0000000000000
--- a/compiler/rustc_codegen_llvm/src/metadata.rs
+++ /dev/null
@@ -1,23 +0,0 @@
-use rustc_target::spec::Target;
-
-use rustc_fs_util::path_to_c_string;
-use std::path::Path;
-use std::slice;
-
-pub fn metadata_section_name(target: &Target) -> &'static str {
-    // 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...
-
-    if target.is_like_osx { "__DATA,.rustc" } else { ".rustc" }
-}

From 3ae15ca04f1ba5db8864b08203462e472cf8630a Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Mon, 29 Mar 2021 13:22:35 +0200
Subject: [PATCH 3/8] Allow wasmparser dependency

---
 src/tools/tidy/src/deps.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/tools/tidy/src/deps.rs b/src/tools/tidy/src/deps.rs
index 064dd716521f5..5f4ba71d91a15 100644
--- a/src/tools/tidy/src/deps.rs
+++ b/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",

From 802fe1756b9fdd6011e17ee6502d6909d2ce55ed Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Fri, 7 May 2021 18:57:22 +0200
Subject: [PATCH 4/8] Disable wasm feature of object in cg_ssa

The version 1 resolver unifies enabled features across the
whole workspace. This includes libstd which isn't allowed
to depend on wasmparser.
---
 compiler/rustc_codegen_ssa/Cargo.toml | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_codegen_ssa/Cargo.toml b/compiler/rustc_codegen_ssa/Cargo.toml
index d7d91d09cfa9f..3fad41f431904 100644
--- a/compiler/rustc_codegen_ssa/Cargo.toml
+++ b/compiler/rustc_codegen_ssa/Cargo.toml
@@ -16,7 +16,6 @@ libc = "0.2.50"
 jobserver = "0.1.22"
 tempfile = "3.2"
 pathdiff = "0.2.0"
-object = "0.22.0"
 
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_ast = { path = "../rustc_ast" }
@@ -34,3 +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"]

From b65a92fdd8b430a1ea421a5bbff08935787999fb Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Mon, 10 May 2021 09:46:02 +0200
Subject: [PATCH 5/8] Remove wasmparser

---
 Cargo.lock                 | 8 --------
 src/tools/tidy/src/deps.rs | 2 --
 2 files changed, 10 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index dc688e3a513cc..189a3b0786c90 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2348,10 +2348,8 @@ 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]]
@@ -5621,12 +5619,6 @@ 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"
diff --git a/src/tools/tidy/src/deps.rs b/src/tools/tidy/src/deps.rs
index 5f4ba71d91a15..064dd716521f5 100644
--- a/src/tools/tidy/src/deps.rs
+++ b/src/tools/tidy/src/deps.rs
@@ -42,7 +42,6 @@ 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)] = &[
@@ -223,7 +222,6 @@ const PERMITTED_DEPENDENCIES: &[&str] = &[
     "vcpkg",
     "version_check",
     "wasi",
-    "wasmparser",
     "winapi",
     "winapi-build",
     "winapi-i686-pc-windows-gnu",

From 487427fbe67480ee7248d775c4ffecd21df12626 Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Mon, 10 May 2021 09:49:42 +0200
Subject: [PATCH 6/8] Better error messages

---
 .../rustc_codegen_ssa/src/back/metadata.rs    | 22 ++++++++++++-------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/compiler/rustc_codegen_ssa/src/back/metadata.rs b/compiler/rustc_codegen_ssa/src/back/metadata.rs
index 096098fb260c7..37d1f8ecc8328 100644
--- a/compiler/rustc_codegen_ssa/src/back/metadata.rs
+++ b/compiler/rustc_codegen_ssa/src/back/metadata.rs
@@ -28,8 +28,10 @@ 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 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()));
 }
@@ -38,16 +40,17 @@ 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))?;
+                .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!("{:?}", e))?;
+                let entry = entry_result
+                    .map_err(|e| format!("failed to parse rlib '{}': {}", path.display(), e))?;
                 if entry.name() == METADATA_FILENAME.as_bytes() {
                     return Ok(entry.data());
                 }
             }
 
-            Err("couldn't find metadata entry".to_string())
+            Err(format!("metadata not found in rlib '{}'", path.display()))
         })
     }
 
@@ -55,11 +58,14 @@ impl MetadataLoader for DefaultMetadataLoader {
         use object::{Object, ObjectSection};
 
         load_metadata_with(path, |data| {
-            let file = object::File::parse(&data).map_err(|e| format!("parse: {:?}", e))?;
+            let file = object::File::parse(&data)
+                .map_err(|e| format!("failed to parse dylib '{}': {}", path.display(), e))?;
             file.section_by_name(".rustc")
-                .ok_or("no .rustc section")?
+                .ok_or_else(|| format!("no .rustc section in '{}'", path.display()))?
                 .data()
-                .map_err(|e| format!("failed to read .rustc section: {:?}", e))
+                .map_err(|e| {
+                    format!("failed to read .rustc section in '{}': {}", path.display(), e)
+                })
         })
     }
 }

From 537e814d9c22d69868272cd472bf30164700c402 Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Mon, 10 May 2021 10:49:45 +0200
Subject: [PATCH 7/8] Add link to historic note

---
 compiler/rustc_codegen_llvm/src/base.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_codegen_llvm/src/base.rs b/compiler/rustc_codegen_llvm/src/base.rs
index aeb0561c08620..893c909b20416 100644
--- a/compiler/rustc_codegen_llvm/src/base.rs
+++ b/compiler/rustc_codegen_llvm/src/base.rs
@@ -58,7 +58,8 @@ pub fn write_compressed_metadata<'tcx>(
     // 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...
+    // `.note.rustc` works on MinGW, see
+    // https://github.com/llvm/llvm-project/blob/llvmorg-12.0.0/lld/COFF/Writer.cpp#L1190-L1197
     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());

From 6381aaf8ae2df01cdb70b6f3123153cf4f1e03cd Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Thu, 13 May 2021 13:03:59 +0200
Subject: [PATCH 8/8] Use DefaultMetadataLoader in the hotplug_codegen_backend
 test

---
 .../hotplug_codegen_backend/the_backend.rs         | 14 +-------------
 1 file changed, 1 insertion(+), 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 0e1bef6f68d53..fce1835c4b2e8 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) {}