Rollup merge of #95589 - Kobzol:rlink-header, r=bjorn3

Include a header in .rlink files

I couldn't find the right place where to put tests. Is there some location that tests `.rlink` creation and loading?
I only found `src/test/run-make-fulldeps/separate-link/Makefile`, but I'm not sure how to check the error message in the Makefile.

Fixes: https://github.com/rust-lang/rust/issues/95297

r? `@bjorn3`

compiler/rustc_codegen_ssa/src/lib.rs

@@ -29,6 +29,7 @@ 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;
@@ -190,3 +191,53 @@ pub fn looks_like_rust_object_file(filename: &str) -> bool {
     // Check if the "inner" extension
     ext2 == Some(RUST_CGU_EXT)
 }
+
+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());
+        rustc_serialize::Encodable::encode(codegen_results, &mut encoder).unwrap();
+        encoder.into_inner()
+    }
+
+    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 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}."
+            ));
+        }
+
+        let codegen_results = CodegenResults::decode(&mut decoder);
+        Ok(codegen_results)
+    }
+}

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 mut decoder = rustc_serialize::opaque::Decoder::new(&rlink_data, 0);
-            let codegen_results: CodegenResults = rustc_serialize::Decodable::decode(&mut decoder);
+            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;
@@ -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(());

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