Use the dummy codegen backend

This allows getting rid of all the argument mangling hacks as well as
the exported_non_generic_symbols override hack by doing cargo build
instead of cargo check. This is also a prerequisite for using native jit
mode support in miri that I hope to add to rustc in the future to be
used with cg_clif too.

Author: bjorn3

cargo-miri/src/phases.rs

@@ -52,18 +52,6 @@ fn show_version() {
     println!();
 }
 
-fn forward_patched_extern_arg(args: &mut impl Iterator<Item = String>, cmd: &mut Command) {
-    cmd.arg("--extern"); // always forward flag, but adjust filename:
-    let path = args.next().expect("`--extern` should be followed by a filename");
-    if let Some(lib) = path.strip_suffix(".rlib") {
-        // If this is an rlib, make it an rmeta.
-        cmd.arg(format!("{lib}.rmeta"));
-    } else {
-        // Some other extern file (e.g. a `.so`). Forward unchanged.
-        cmd.arg(path);
-    }
-}
-
 pub fn phase_cargo_miri(mut args: impl Iterator<Item = String>) {
     // Require a subcommand before any flags.
     // We cannot know which of those flags take arguments and which do not,
@@ -444,7 +432,6 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
     }
 
     let mut cmd = miri();
-    let mut emit_link_hack = false;
     // Arguments are treated very differently depending on whether this crate is
     // for interpretation by Miri, or for use by a build script / proc macro.
     if target_crate {
@@ -455,7 +442,7 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
         }
 
         // Forward arguments, but patched.
-        let emit_flag = "--emit";
+
         // This hack helps bootstrap run standard library tests in Miri. The issue is as follows:
         // when running `cargo miri test` on libcore, cargo builds a local copy of core and makes it
         // a dependency of the integration test crate. This copy duplicates all the lang items, so
@@ -472,29 +459,6 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
             && !runnable_crate
             && phase == RustcPhase::Build;
         while let Some(arg) = args.next() {
-            // Patch `--emit`: remove "link" from "--emit" to make this a check-only build.
-            if let Some(val) = arg.strip_prefix(emit_flag) {
-                // Patch this argument. First, extract its value.
-                let val =
-                    val.strip_prefix('=').expect("`cargo` should pass `--emit=X` as one argument");
-                let mut val: Vec<_> = val.split(',').collect();
-                // Now make sure "link" is not in there, but "metadata" is.
-                if let Some(i) = val.iter().position(|&s| s == "link") {
-                    emit_link_hack = true;
-                    val.remove(i);
-                    if !val.contains(&"metadata") {
-                        val.push("metadata");
-                    }
-                }
-                cmd.arg(format!("{emit_flag}={}", val.join(",")));
-                continue;
-            }
-            // Patch `--extern` filenames, since Cargo sometimes passes stub `.rlib` files:
-            // https://github.com/rust-lang/miri/issues/1705
-            if arg == "--extern" {
-                forward_patched_extern_arg(&mut args, &mut cmd);
-                continue;
-            }
             // If the REPLACE_LIBRS hack is enabled and we are building a `lib.rs` file, and a
             // `lib.miri.rs` file exists, then build that instead.
             if replace_librs {
@@ -543,17 +507,6 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
         eprintln!("[cargo-miri rustc] target_crate={target_crate} runnable_crate={runnable_crate}");
     }
 
-    // Create a stub .rlib file if "link" was requested by cargo.
-    // This is necessary to prevent cargo from doing rebuilds all the time.
-    if emit_link_hack {
-        for filename in out_filenames() {
-            if verbose > 0 {
-                eprintln!("[cargo-miri rustc] creating fake lib file at `{}`", filename.display());
-            }
-            File::create(filename).expect("failed to create fake lib file");
-        }
-    }
-
     debug_cmd("[cargo-miri rustc]", verbose, &cmd);
     exec(cmd);
 }
@@ -624,17 +577,12 @@ pub fn phase_runner(mut binary_args: impl Iterator<Item = String>, phase: Runner
         cmd.arg("--sysroot").arg(env::var_os("MIRI_SYSROOT").unwrap());
     }
     // Forward rustc arguments.
-    // We need to patch "--extern" filenames because we forced a check-only
-    // build without cargo knowing about that: replace `.rlib` suffix by
-    // `.rmeta`.
-    // We also need to remove `--error-format` as cargo specifies that to be JSON,
+    // We need to remove `--error-format` as cargo specifies that to be JSON,
     // but when we run here, cargo does not interpret the JSON any more. `--json`
     // then also needs to be dropped.
     let mut args = info.args.iter();
     while let Some(arg) = args.next() {
-        if arg == "--extern" {
-            forward_patched_extern_arg(&mut (&mut args).cloned(), &mut cmd);
-        } else if let Some(suffix) = arg.strip_prefix("--error-format") {
+        if let Some(suffix) = arg.strip_prefix("--error-format") {
             assert!(suffix.starts_with('='));
             // Drop this argument.
         } else if let Some(suffix) = arg.strip_prefix("--json") {
@@ -668,23 +616,15 @@ pub fn phase_runner(mut binary_args: impl Iterator<Item = String>, phase: Runner
     }
 }
 
-pub fn phase_rustdoc(mut args: impl Iterator<Item = String>) {
+pub fn phase_rustdoc(args: impl Iterator<Item = String>) {
     let verbose = env::var("MIRI_VERBOSE")
         .map_or(0, |verbose| verbose.parse().expect("verbosity flag must be an integer"));
 
     // phase_cargo_miri sets the RUSTDOC env var to ourselves, and puts a backup
     // of the old value into MIRI_ORIG_RUSTDOC. So that's what we have to invoke now.
     let rustdoc = env::var("MIRI_ORIG_RUSTDOC").unwrap_or("rustdoc".to_string());
     let mut cmd = Command::new(rustdoc);
-
-    while let Some(arg) = args.next() {
-        if arg == "--extern" {
-            // Patch --extern arguments to use *.rmeta files, since phase_cargo_rustc only creates stub *.rlib files.
-            forward_patched_extern_arg(&mut args, &mut cmd);
-        } else {
-            cmd.arg(arg);
-        }
-    }
+    cmd.args(args);
 
     // Doctests of `proc-macro` crates (and their dependencies) are always built for the host,
     // so we are not able to run them in Miri.

cargo-miri/src/setup.rs

@@ -160,7 +160,7 @@ pub fn setup(
 
     // Do the build.
     let status = SysrootBuilder::new(&sysroot_dir, target)
-        .build_mode(BuildMode::Check)
+        .build_mode(BuildMode::Build)
         .rustc_version(rustc_version.clone())
         .sysroot_config(sysroot_config)
         .rustflags(rustflags)

rust-version

@@ -1 +1 @@
-292be5c7c05138d753bbd4b30db7a3f1a5c914f7
+72fe2ffb391f397efdfafb2216028ed9952e8078

src/bin/miri.rs

@@ -16,7 +16,6 @@ extern crate rustc_hir;
 extern crate rustc_hir_analysis;
 extern crate rustc_interface;
 extern crate rustc_log;
-extern crate rustc_metadata;
 extern crate rustc_middle;
 extern crate rustc_session;
 extern crate rustc_span;
@@ -26,10 +25,8 @@ mod log;
 use std::env;
 use std::num::NonZero;
 use std::ops::Range;
-use std::path::PathBuf;
 use std::rc::Rc;
 use std::str::FromStr;
-use std::sync::Arc;
 use std::sync::atomic::{AtomicI32, AtomicU32, Ordering};
 
 use miri::{
@@ -51,10 +48,8 @@ use rustc_middle::middle::exported_symbols::{
 use rustc_middle::query::LocalCrate;
 use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
 use rustc_middle::ty::{self, Ty, TyCtxt};
-use rustc_middle::util::Providers;
 use rustc_session::EarlyDiagCtxt;
 use rustc_session::config::{CrateType, ErrorOutputType, OptLevel};
-use rustc_session::search_paths::PathKind;
 use rustc_span::def_id::DefId;
 
 use crate::log::setup::{deinit_loggers, init_early_loggers, init_late_loggers};
@@ -126,21 +121,6 @@ fn entry_fn(tcx: TyCtxt<'_>) -> (DefId, MiriEntryFnType) {
 }
 
 impl rustc_driver::Callbacks for MiriCompilerCalls {
-    fn config(&mut self, config: &mut Config) {
-        config.override_queries = Some(|_, providers| {
-            providers.extern_queries.used_crate_source = |tcx, cnum| {
-                let mut providers = Providers::default();
-                rustc_metadata::provide(&mut providers);
-                let mut crate_source = (providers.extern_queries.used_crate_source)(tcx, cnum);
-                // HACK: rustc will emit "crate ... required to be available in rlib format, but
-                // was not found in this form" errors once we use `tcx.dependency_formats()` if
-                // there's no rlib provided, so setting a dummy path here to workaround those errors.
-                Arc::make_mut(&mut crate_source).rlib = Some((PathBuf::new(), PathKind::All));
-                crate_source
-            };
-        });
-    }
-
     fn after_analysis<'tcx>(
         &mut self,
         _: &rustc_interface::interface::Compiler,
@@ -256,9 +236,8 @@ impl rustc_driver::Callbacks for MiriBeRustCompilerCalls {
             // Queries overridden here affect the data stored in `rmeta` files of dependencies,
             // which will be used later in non-`MIRI_BE_RUSTC` mode.
             config.override_queries = Some(|_, local_providers| {
-                // `exported_non_generic_symbols` and `reachable_non_generics` provided by rustc always returns
-                // an empty result if `tcx.sess.opts.output_types.should_codegen()` is false.
-                // In addition we need to add #[used] symbols to exported_symbols for `lookup_link_section`.
+                // We need to add #[used] symbols to exported_symbols for `lookup_link_section`.
+                // FIXME handle this somehow in rustc itself to avoid this hack
                 local_providers.exported_non_generic_symbols = |tcx, LocalCrate| {
                     let reachable_set = tcx.with_stable_hashing_context(|hcx| {
                         tcx.reachable_set(()).to_sorted(&hcx, true)

src/lib.rs

@@ -165,6 +165,7 @@ pub use crate::shims::unwind::{CatchUnwindData, EvalContextExt as _};
 /// Also disable the MIR pass that inserts an alignment check on every pointer dereference. Miri
 /// does that too, and with a better error message.
 pub const MIRI_DEFAULT_ARGS: &[&str] = &[
+    "-Zcodegen-backend=dummy",
     "--cfg=miri",
     "-Zalways-encode-mir",
     "-Zextra-const-ub-checks",