Support running no_core Linux programs

src/eval.rs

@@ -21,6 +21,7 @@ use rustc_target::spec::Os;
 use crate::concurrency::GenmcCtx;
 use crate::concurrency::thread::TlsAllocAction;
 use crate::diagnostics::report_leaks;
+use crate::helpers::is_no_core;
 use crate::shims::{global_ctor, tls};
 use crate::*;
 
@@ -289,14 +290,20 @@ pub fn create_ecx<'tcx>(
         MiriMachine::new(config, layout_cx, genmc_ctx),
     );
 
-    // Make sure we have MIR. We check MIR for some stable monomorphic function in libcore.
-    let sentinel =
-        helpers::try_resolve_path(tcx, &["core", "ascii", "escape_default"], Namespace::ValueNS);
-    if !matches!(sentinel, Some(s) if tcx.is_mir_available(s.def.def_id())) {
-        tcx.dcx().fatal(
-            "the current sysroot was built without `-Zalways-encode-mir`, or libcore seems missing.\n\
-            Note that directly invoking the `miri` binary is not supported; please use `cargo miri` instead."
+    // Make sure we have MIR. We check MIR for some stable monomorphic function in libcore, except
+    // if the current crate is #![no_core] it's fine to be missing the usual items from libcore.
+    if !is_no_core(tcx) {
+        let sentinel = helpers::try_resolve_path(
+            tcx,
+            &["core", "ascii", "escape_default"],
+            Namespace::ValueNS,
         );
+        if !matches!(sentinel, Some(s) if tcx.is_mir_available(s.def.def_id())) {
+            tcx.dcx().fatal(
+                "the current sysroot was built without `-Zalways-encode-mir`, or libcore seems missing.\n\
+                Note that directly invoking the `miri` binary is not supported; please use `cargo miri` instead."
+            );
+        }
     }
 
     // Compute argc and argv from `config.args`.

src/helpers.rs

@@ -1089,6 +1089,11 @@ pub(crate) fn windows_check_buffer_size((success, len): (bool, u64)) -> u32 {
     }
 }
 
+/// Check whether the local crate has the `#![no_core]` attribute.
+pub fn is_no_core(tcx: TyCtxt<'_>) -> bool {
+    rustc_hir::find_attr!(tcx, crate, NoCore(..))
+}
+
 /// We don't support 16-bit systems, so let's have ergonomic conversion from `u32` to `usize`.
 pub trait ToUsize {
     fn to_usize(self) -> usize;

src/machine.rs

@@ -40,6 +40,7 @@ use crate::concurrency::sync::SyncObj;
 use crate::concurrency::{
     AllocDataRaceHandler, GenmcCtx, GenmcEvalContextExt as _, GlobalDataRaceHandler, weak_memory,
 };
+use crate::helpers::is_no_core;
 use crate::*;
 
 /// First real-time signal.
@@ -731,7 +732,8 @@ impl<'tcx> MiriMachine<'tcx> {
         );
         let threads = ThreadManager::new(config);
         let mut thread_cpu_affinity = FxHashMap::default();
-        if matches!(&tcx.sess.target.os, Os::Linux | Os::FreeBsd | Os::Android) {
+        if matches!(&tcx.sess.target.os, Os::Linux | Os::FreeBsd | Os::Android) && !is_no_core(tcx)
+        {
             thread_cpu_affinity
                 .insert(threads.active_thread(), CpuAffinityMask::new(&layout_cx, config.num_cpus));
         }

tests/pass/no_core.rs

@@ -0,0 +1,22 @@
+//! Test that Miri is able to run no_core programs.
+//! This ensures that we don't depend on any paths from core when no_core is set.
+
+#![no_std]
+#![no_core]
+#![no_main]
+#![feature(rustc_attrs, no_core, lang_items, intrinsics)]
+#![allow(internal_features)]
+
+#[lang = "pointee_sized"]
+pub trait PointeeSized {}
+
+#[lang = "meta_sized"]
+pub trait MetaSized: PointeeSized {}
+
+#[lang = "sized"]
+pub trait Sized: MetaSized {}
+
+#[no_mangle]
+fn miri_start(_argc: isize, _argv: *const *const u8) -> isize {
+    0
+}