From e0d42266770dcdb3578a2ea7e14ee91967156a2e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jakub=20Ber=C3=A1nek?= <berykubik@gmail.com>
Date: Sat, 2 Apr 2022 16:50:08 +0200
Subject: [PATCH] Include a header in .rlink files to provide nicer error
 messages when a wrong file is parsed as .rlink

---
 compiler/rustc_codegen_ssa/src/lib.rs   | 31 +++++++++++++++++++++++++
 compiler/rustc_driver/src/lib.rs        |  4 ++--
 compiler/rustc_interface/src/queries.rs |  6 ++---
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/compiler/rustc_codegen_ssa/src/lib.rs b/compiler/rustc_codegen_ssa/src/lib.rs
index 6cf6be79a862..38d76afc0e66 100644
--- a/compiler/rustc_codegen_ssa/src/lib.rs
+++ b/compiler/rustc_codegen_ssa/src/lib.rs
@@ -34,6 +34,7 @@ use rustc_session::cstore::{self, CrateSource};
 use rustc_session::utils::NativeLibKind;
 use rustc_span::symbol::Symbol;
 use std::path::{Path, PathBuf};
+use rustc_serialize::{Decodable, Decoder, Encoder, opaque};
 
 pub mod back;
 pub mod base;
@@ -190,3 +191,33 @@ pub fn looks_like_rust_object_file(filename: &str) -> bool {
     // Check if the "inner" extension
     ext2 == Some(RUST_CGU_EXT)
 }
+
+const RLINK_MAGIC: &'static [u8; 5] = b"rlink";
+const RUSTC_VERSION: Option<&str> = option_env!("CFG_VERSION");
+
+impl CodegenResults {
+    pub fn serialize_rlink(codegen_results: &CodegenResults) -> Vec<u8> {
+        let mut encoder = opaque::Encoder::new(vec![]);
+        encoder.emit_raw_bytes(RLINK_MAGIC).unwrap();
+        encoder.emit_str(RUSTC_VERSION.unwrap()).unwrap();
+
+        let mut encoder = rustc_serialize::opaque::Encoder::new(encoder.into_inner());
+        rustc_serialize::Encodable::encode(codegen_results, &mut encoder).unwrap();
+        encoder.into_inner()
+    }
+
+    pub fn deserialize_rlink(data: Vec<u8>) -> Result<Self, String> {
+        if !data.starts_with(RLINK_MAGIC) {
+            return Err("The input does not look like a .rlink file".to_string());
+        }
+        let mut decoder = opaque::Decoder::new(&data[RLINK_MAGIC.len()..], 0);
+        let rustc_version = decoder.read_str();
+        let current_version = RUSTC_VERSION.unwrap();
+        if rustc_version != current_version {
+            return Err(format!(".rlink file was produced by rustc version {rustc_version}, but the current version is {current_version}."));
+        }
+
+        let codegen_results = CodegenResults::decode(&mut decoder);
+        Ok(codegen_results)
+    }
+}
diff --git a/compiler/rustc_driver/src/lib.rs b/compiler/rustc_driver/src/lib.rs
index 667c63b709b7..a788ee26647e 100644
--- a/compiler/rustc_driver/src/lib.rs
+++ b/compiler/rustc_driver/src/lib.rs
@@ -588,8 +588,8 @@ pub fn try_process_rlink(sess: &Session, compiler: &interface::Compiler) -> Comp
             let rlink_data = fs::read(file).unwrap_or_else(|err| {
                 sess.fatal(&format!("failed to read rlink file: {}", err));
             });
-            let mut decoder = rustc_serialize::opaque::Decoder::new(&rlink_data, 0);
-            let codegen_results: CodegenResults = rustc_serialize::Decodable::decode(&mut decoder);
+            let codegen_results = CodegenResults::deserialize_rlink(rlink_data)
+                .expect("Could not deserialize .rlink file");
             let result = compiler.codegen_backend().link(sess, codegen_results, &outputs);
             abort_on_err(result, sess);
         } else {
diff --git a/compiler/rustc_interface/src/queries.rs b/compiler/rustc_interface/src/queries.rs
index 6373f4e9af19..930715bba267 100644
--- a/compiler/rustc_interface/src/queries.rs
+++ b/compiler/rustc_interface/src/queries.rs
@@ -18,6 +18,7 @@ use rustc_span::symbol::sym;
 use std::any::Any;
 use std::cell::{Ref, RefCell, RefMut};
 use std::rc::Rc;
+use rustc_codegen_ssa::CodegenResults;
 
 /// Represent the result of a query.
 ///
@@ -360,10 +361,9 @@ impl Linker {
         }
 
         if sess.opts.debugging_opts.no_link {
-            let mut encoder = rustc_serialize::opaque::Encoder::new(Vec::new());
-            rustc_serialize::Encodable::encode(&codegen_results, &mut encoder).unwrap();
+            let encoded = CodegenResults::serialize_rlink(&codegen_results);
             let rlink_file = self.prepare_outputs.with_extension(config::RLINK_EXT);
-            std::fs::write(&rlink_file, encoder.into_inner()).map_err(|err| {
+            std::fs::write(&rlink_file, encoded).map_err(|err| {
                 sess.fatal(&format!("failed to write file {}: {}", rlink_file.display(), err));
             })?;
             return Ok(());