Address review comments and add a test

compiler/rustc_codegen_ssa/src/lib.rs

@@ -29,12 +29,12 @@ use rustc_hir::LangItem;
 use rustc_middle::dep_graph::WorkProduct;
 use rustc_middle::middle::dependency_format::Dependencies;
 use rustc_middle::ty::query::{ExternProviders, Providers};
+use rustc_serialize::{opaque, Decodable, Decoder, Encoder};
 use rustc_session::config::{CrateType, OutputFilenames, OutputType, RUST_CGU_EXT};
 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;
@@ -192,13 +192,18 @@ pub fn looks_like_rust_object_file(filename: &str) -> bool {
     ext2 == Some(RUST_CGU_EXT)
 }
 
-const RLINK_MAGIC: &'static [u8; 5] = b"rlink";
+const RLINK_VERSION: u32 = 1;
+const RLINK_MAGIC: &[u8] = b"rustlink";
+
 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();
+        // `emit_raw_bytes` is used to make sure that the version representation does not depend on
+        // Encoder's inner representation of `u32`.
+        encoder.emit_raw_bytes(&RLINK_VERSION.to_be_bytes()).unwrap();
         encoder.emit_str(RUSTC_VERSION.unwrap()).unwrap();
 
         let mut encoder = rustc_serialize::opaque::Encoder::new(encoder.into_inner());
@@ -207,14 +212,29 @@ impl CodegenResults {
     }
 
     pub fn deserialize_rlink(data: Vec<u8>) -> Result<Self, String> {
+        // The Decodable machinery is not used here because it panics if the input data is invalid
+        // and because its internal representation may change.
         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 data = &data[RLINK_MAGIC.len()..];
+        if data.len() < 4 {
+            return Err("The input does not contain version number".to_string());
+        }
+
+        let mut version_array: [u8; 4] = Default::default();
+        version_array.copy_from_slice(&data[..4]);
+        if u32::from_be_bytes(version_array) != RLINK_VERSION {
+            return Err(".rlink file was produced with encoding version {version_array}, but the current version is {RLINK_VERSION}".to_string());
+        }
+
+        let mut decoder = opaque::Decoder::new(&data[4..], 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}."));
+            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);

compiler/rustc_driver/src/lib.rs

@@ -588,8 +588,12 @@ 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 codegen_results = CodegenResults::deserialize_rlink(rlink_data)
-                .expect("Could not deserialize .rlink file");
+            let codegen_results = match CodegenResults::deserialize_rlink(rlink_data) {
+                Ok(codegen) => codegen,
+                Err(error) => {
+                    sess.fatal(&format!("Could not deserialize .rlink file: {error}"));
+                }
+            };
             let result = compiler.codegen_backend().link(sess, codegen_results, &outputs);
             abort_on_err(result, sess);
         } else {

compiler/rustc_interface/src/queries.rs

@@ -3,6 +3,7 @@ use crate::passes::{self, BoxedResolver, QueryContext};
 
 use rustc_ast as ast;
 use rustc_codegen_ssa::traits::CodegenBackend;
+use rustc_codegen_ssa::CodegenResults;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::{Lrc, OnceCell, WorkerLocal};
 use rustc_hir::def_id::LOCAL_CRATE;
@@ -18,7 +19,6 @@ 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.
 ///

src/test/run-make-fulldeps/separate-link-fail/Makefile

@@ -0,0 +1,7 @@
+-include ../tools.mk
+
+all:
+	echo 'fn main(){}' > $(TMPDIR)/main.rs
+	# Make sure that this fails
+	! $(RUSTC) -Z link-only $(TMPDIR)/main.rs 2> $(TMPDIR)/stderr.txt
+	$(CGREP) "The input does not look like a .rlink file" < $(TMPDIR)/stderr.txt