diff --git a/src/librustc_expand/base.rs b/src/librustc_expand/base.rs
index eeb30e2ced99b..13637e58c9364 100644
--- a/src/librustc_expand/base.rs
+++ b/src/librustc_expand/base.rs
@@ -1095,7 +1095,7 @@ impl<'a> ExtCtxt<'a> {
         if !path.is_absolute() {
             let callsite = span.source_callsite();
             let mut result = match self.source_map().span_to_unmapped_path(callsite) {
-                FileName::Real(path) => path,
+                FileName::Real(name) => name.into_local_path(),
                 FileName::DocTest(path, _) => path,
                 other => {
                     return Err(self.struct_span_err(
diff --git a/src/librustc_expand/expand.rs b/src/librustc_expand/expand.rs
index 09ba64204c5c3..5214ca0dc7fff 100644
--- a/src/librustc_expand/expand.rs
+++ b/src/librustc_expand/expand.rs
@@ -341,7 +341,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         let mut module = ModuleData {
             mod_path: vec![Ident::from_str(&self.cx.ecfg.crate_name)],
             directory: match self.cx.source_map().span_to_unmapped_path(krate.span) {
-                FileName::Real(path) => path,
+                FileName::Real(name) => name.into_local_path(),
                 other => PathBuf::from(other.to_string()),
             },
         };
diff --git a/src/librustc_expand/module.rs b/src/librustc_expand/module.rs
index 9bb2b57b7f591..82215c7297ed6 100644
--- a/src/librustc_expand/module.rs
+++ b/src/librustc_expand/module.rs
@@ -71,7 +71,7 @@ crate fn parse_external_mod(
     // Extract the directory path for submodules of `module`.
     let path = sess.source_map().span_to_unmapped_path(module.inner);
     let mut path = match path {
-        FileName::Real(path) => path,
+        FileName::Real(name) => name.into_local_path(),
         other => PathBuf::from(other.to_string()),
     };
     path.pop();
@@ -189,7 +189,8 @@ fn error_cannot_declare_mod_here<'a, T>(
     let mut err =
         sess.span_diagnostic.struct_span_err(span, "cannot declare a new module at this location");
     if !span.is_dummy() {
-        if let FileName::Real(src_path) = sess.source_map().span_to_filename(span) {
+        if let FileName::Real(src_name) = sess.source_map().span_to_filename(span) {
+            let src_path = src_name.into_local_path();
             if let Some(stem) = src_path.file_stem() {
                 let mut dest_path = src_path.clone();
                 dest_path.set_file_name(stem);
diff --git a/src/librustc_expand/proc_macro_server.rs b/src/librustc_expand/proc_macro_server.rs
index b9693c2c86278..36af83711f7e4 100644
--- a/src/librustc_expand/proc_macro_server.rs
+++ b/src/librustc_expand/proc_macro_server.rs
@@ -602,7 +602,8 @@ impl server::SourceFile for Rustc<'_> {
     }
     fn path(&mut self, file: &Self::SourceFile) -> String {
         match file.name {
-            FileName::Real(ref path) => path
+            FileName::Real(ref name) => name
+                .local_path()
                 .to_str()
                 .expect("non-UTF8 file path in `proc_macro::SourceFile::path`")
                 .to_string(),
diff --git a/src/librustc_interface/passes.rs b/src/librustc_interface/passes.rs
index c06fd91133b5c..a01170db807f2 100644
--- a/src/librustc_interface/passes.rs
+++ b/src/librustc_interface/passes.rs
@@ -33,7 +33,7 @@ use rustc_session::output::{filename_for_input, filename_for_metadata};
 use rustc_session::search_paths::PathKind;
 use rustc_session::Session;
 use rustc_span::symbol::Symbol;
-use rustc_span::FileName;
+use rustc_span::{FileName, RealFileName};
 use rustc_trait_selection::traits;
 use rustc_typeck as typeck;
 
@@ -569,13 +569,16 @@ fn write_out_deps(
                 for cnum in resolver.cstore().crates_untracked() {
                     let source = resolver.cstore().crate_source_untracked(cnum);
                     if let Some((path, _)) = source.dylib {
-                        files.push(escape_dep_filename(&FileName::Real(path)));
+                        let file_name = FileName::Real(RealFileName::Named(path));
+                        files.push(escape_dep_filename(&file_name));
                     }
                     if let Some((path, _)) = source.rlib {
-                        files.push(escape_dep_filename(&FileName::Real(path)));
+                        let file_name = FileName::Real(RealFileName::Named(path));
+                        files.push(escape_dep_filename(&file_name));
                     }
                     if let Some((path, _)) = source.rmeta {
-                        files.push(escape_dep_filename(&FileName::Real(path)));
+                        let file_name = FileName::Real(RealFileName::Named(path));
+                        files.push(escape_dep_filename(&file_name));
                     }
                 }
             });
diff --git a/src/librustc_metadata/rmeta/decoder.rs b/src/librustc_metadata/rmeta/decoder.rs
index 2b292b35c159d..f5a9dceb78295 100644
--- a/src/librustc_metadata/rmeta/decoder.rs
+++ b/src/librustc_metadata/rmeta/decoder.rs
@@ -1471,15 +1471,22 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
 
             if let Some(virtual_dir) = virtual_rust_source_base_dir {
                 if let Some(real_dir) = &sess.real_rust_source_base_dir {
-                    if let rustc_span::FileName::Real(path) = name {
-                        if let Ok(rest) = path.strip_prefix(virtual_dir) {
-                            let new_path = real_dir.join(rest);
-                            debug!(
-                                "try_to_translate_virtual_to_real: `{}` -> `{}`",
-                                path.display(),
-                                new_path.display(),
-                            );
-                            *path = new_path;
+                    if let rustc_span::FileName::Real(old_name) = name {
+                        if let rustc_span::RealFileName::Named(one_path) = old_name {
+                            if let Ok(rest) = one_path.strip_prefix(virtual_dir) {
+                                let virtual_name = one_path.clone();
+                                let new_path = real_dir.join(rest);
+                                debug!(
+                                    "try_to_translate_virtual_to_real: `{}` -> `{}`",
+                                    virtual_name.display(),
+                                    new_path.display(),
+                                );
+                                let new_name = rustc_span::RealFileName::Devirtualized {
+                                    local_path: new_path,
+                                    virtual_name,
+                                };
+                                *old_name = new_name;
+                            }
                         }
                     }
                 }
diff --git a/src/librustc_metadata/rmeta/encoder.rs b/src/librustc_metadata/rmeta/encoder.rs
index 91fbfcc0133eb..9964c9c94c951 100644
--- a/src/librustc_metadata/rmeta/encoder.rs
+++ b/src/librustc_metadata/rmeta/encoder.rs
@@ -396,6 +396,7 @@ impl<'tcx> EncodeContext<'tcx> {
                     // any relative paths are potentially relative to a
                     // wrong directory.
                     FileName::Real(ref name) => {
+                        let name = name.stable_name();
                         let mut adapted = (**source_file).clone();
                         adapted.name = Path::new(&working_dir).join(name).into();
                         adapted.name_hash = {
diff --git a/src/librustc_save_analysis/span_utils.rs b/src/librustc_save_analysis/span_utils.rs
index 6620941c44046..d5f992b0de05d 100644
--- a/src/librustc_save_analysis/span_utils.rs
+++ b/src/librustc_save_analysis/span_utils.rs
@@ -16,12 +16,13 @@ impl<'a> SpanUtils<'a> {
 
     pub fn make_filename_string(&self, file: &SourceFile) -> String {
         match &file.name {
-            FileName::Real(path) if !file.name_was_remapped => {
+            FileName::Real(name) if !file.name_was_remapped => {
+                let path = name.local_path();
                 if path.is_absolute() {
                     self.sess
                         .source_map()
                         .path_mapping()
-                        .map_prefix(path.clone())
+                        .map_prefix(path.into())
                         .0
                         .display()
                         .to_string()
diff --git a/src/librustc_span/lib.rs b/src/librustc_span/lib.rs
index 616876d4b02a8..c7d2205eb1c27 100644
--- a/src/librustc_span/lib.rs
+++ b/src/librustc_span/lib.rs
@@ -53,7 +53,7 @@ use std::cmp::{self, Ordering};
 use std::fmt;
 use std::hash::Hash;
 use std::ops::{Add, Sub};
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::str::FromStr;
 
 use md5::Md5;
@@ -81,11 +81,61 @@ impl Globals {
 
 scoped_tls::scoped_thread_local!(pub static GLOBALS: Globals);
 
+// FIXME: Perhaps this should not implement Rustc{Decodable, Encodable}
+//
+// FIXME: We should use this enum or something like it to get rid of the
+// use of magic `/rust/1.x/...` paths across the board.
+#[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd, Hash, RustcDecodable, RustcEncodable)]
+#[derive(HashStable_Generic)]
+pub enum RealFileName {
+    Named(PathBuf),
+    /// For de-virtualized paths (namely paths into libstd that have been mapped
+    /// to the appropriate spot on the local host's file system),
+    Devirtualized {
+        /// `local_path` is the (host-dependent) local path to the file.
+        local_path: PathBuf,
+        /// `virtual_name` is the stable path rustc will store internally within
+        /// build artifacts.
+        virtual_name: PathBuf,
+    },
+}
+
+impl RealFileName {
+    /// Returns the path suitable for reading from the file system on the local host.
+    /// Avoid embedding this in build artifacts; see `stable_name` for that.
+    pub fn local_path(&self) -> &Path {
+        match self {
+            RealFileName::Named(p)
+            | RealFileName::Devirtualized { local_path: p, virtual_name: _ } => &p,
+        }
+    }
+
+    /// Returns the path suitable for reading from the file system on the local host.
+    /// Avoid embedding this in build artifacts; see `stable_name` for that.
+    pub fn into_local_path(self) -> PathBuf {
+        match self {
+            RealFileName::Named(p)
+            | RealFileName::Devirtualized { local_path: p, virtual_name: _ } => p,
+        }
+    }
+
+    /// Returns the path suitable for embedding into build artifacts. Note that
+    /// a virtualized path will not correspond to a valid file system path; see
+    /// `local_path` for something that is more likely to return paths into the
+    /// local host file system.
+    pub fn stable_name(&self) -> &Path {
+        match self {
+            RealFileName::Named(p)
+            | RealFileName::Devirtualized { local_path: _, virtual_name: p } => &p,
+        }
+    }
+}
+
 /// Differentiates between real files and common virtual files.
 #[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd, Hash, RustcDecodable, RustcEncodable)]
 #[derive(HashStable_Generic)]
 pub enum FileName {
-    Real(PathBuf),
+    Real(RealFileName),
     /// Call to `quote!`.
     QuoteExpansion(u64),
     /// Command line.
@@ -109,7 +159,13 @@ impl std::fmt::Display for FileName {
     fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         use FileName::*;
         match *self {
-            Real(ref path) => write!(fmt, "{}", path.display()),
+            Real(RealFileName::Named(ref path)) => write!(fmt, "{}", path.display()),
+            // FIXME: might be nice to display both compoments of Devirtualized.
+            // But for now (to backport fix for issue #70924), best to not
+            // perturb diagnostics so its obvious test suite still works.
+            Real(RealFileName::Devirtualized { ref local_path, virtual_name: _ }) => {
+                write!(fmt, "{}", local_path.display())
+            }
             QuoteExpansion(_) => write!(fmt, "<quote expansion>"),
             MacroExpansion(_) => write!(fmt, "<macro expansion>"),
             Anon(_) => write!(fmt, "<anon>"),
@@ -126,7 +182,7 @@ impl std::fmt::Display for FileName {
 impl From<PathBuf> for FileName {
     fn from(p: PathBuf) -> Self {
         assert!(!p.to_string_lossy().ends_with('>'));
-        FileName::Real(p)
+        FileName::Real(RealFileName::Named(p))
     }
 }
 
diff --git a/src/librustc_span/source_map.rs b/src/librustc_span/source_map.rs
index 51f5541766305..c33c1dd29cb72 100644
--- a/src/librustc_span/source_map.rs
+++ b/src/librustc_span/source_map.rs
@@ -86,6 +86,8 @@ impl FileLoader for RealFileLoader {
 #[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
 pub struct StableSourceFileId(u128);
 
+// FIXME: we need a more globally consistent approach to the problem solved by
+// StableSourceFileId, perhaps built atop source_file.name_hash.
 impl StableSourceFileId {
     pub fn new(source_file: &SourceFile) -> StableSourceFileId {
         StableSourceFileId::new_from_pieces(
@@ -95,14 +97,21 @@ impl StableSourceFileId {
         )
     }
 
-    pub fn new_from_pieces(
+    fn new_from_pieces(
         name: &FileName,
         name_was_remapped: bool,
         unmapped_path: Option<&FileName>,
     ) -> StableSourceFileId {
         let mut hasher = StableHasher::new();
 
-        name.hash(&mut hasher);
+        if let FileName::Real(real_name) = name {
+            // rust-lang/rust#70924: Use the stable (virtualized) name when
+            // available. (We do not want artifacts from transient file system
+            // paths for libstd to leak into our build artifacts.)
+            real_name.stable_name().hash(&mut hasher)
+        } else {
+            name.hash(&mut hasher);
+        }
         name_was_remapped.hash(&mut hasher);
         unmapped_path.hash(&mut hasher);
 
@@ -235,7 +244,7 @@ impl SourceMap {
 
     fn try_new_source_file(
         &self,
-        filename: FileName,
+        mut filename: FileName,
         src: String,
     ) -> Result<Lrc<SourceFile>, OffsetOverflowError> {
         // The path is used to determine the directory for loading submodules and
@@ -245,13 +254,22 @@ impl SourceMap {
         // be empty, so the working directory will be used.
         let unmapped_path = filename.clone();
 
-        let (filename, was_remapped) = match filename {
-            FileName::Real(filename) => {
-                let (filename, was_remapped) = self.path_mapping.map_prefix(filename);
-                (FileName::Real(filename), was_remapped)
+        let was_remapped;
+        if let FileName::Real(real_filename) = &mut filename {
+            match real_filename {
+                RealFileName::Named(path_to_be_remapped)
+                | RealFileName::Devirtualized {
+                    local_path: path_to_be_remapped,
+                    virtual_name: _,
+                } => {
+                    let mapped = self.path_mapping.map_prefix(path_to_be_remapped.clone());
+                    was_remapped = mapped.1;
+                    *path_to_be_remapped = mapped.0;
+                }
             }
-            other => (other, false),
-        };
+        } else {
+            was_remapped = false;
+        }
 
         let file_id =
             StableSourceFileId::new_from_pieces(&filename, was_remapped, Some(&unmapped_path));
@@ -998,7 +1016,7 @@ impl SourceMap {
     }
     pub fn ensure_source_file_source_present(&self, source_file: Lrc<SourceFile>) -> bool {
         source_file.add_external_src(|| match source_file.name {
-            FileName::Real(ref name) => self.file_loader.read_file(name).ok(),
+            FileName::Real(ref name) => self.file_loader.read_file(name.local_path()).ok(),
             _ => None,
         })
     }
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index 5b364ed95cf59..07631093edda4 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -473,7 +473,7 @@ pub fn run(
     } = options;
 
     let src_root = match krate.src {
-        FileName::Real(ref p) => match p.parent() {
+        FileName::Real(ref p) => match p.local_path().parent() {
             Some(p) => p.to_path_buf(),
             None => PathBuf::new(),
         },
@@ -1621,9 +1621,10 @@ impl Context {
 
         // We can safely ignore synthetic `SourceFile`s.
         let file = match item.source.filename {
-            FileName::Real(ref path) => path,
+            FileName::Real(ref path) => path.local_path().to_path_buf(),
             _ => return None,
         };
+        let file = &file;
 
         let (krate, path) = if item.source.cnum == LOCAL_CRATE {
             if let Some(path) = self.shared.local_sources.get(file) {
diff --git a/src/librustdoc/html/render/cache.rs b/src/librustdoc/html/render/cache.rs
index 57d385de32096..225940773413e 100644
--- a/src/librustdoc/html/render/cache.rs
+++ b/src/librustdoc/html/render/cache.rs
@@ -173,7 +173,7 @@ impl Cache {
         // Cache where all our extern crates are located
         for &(n, ref e) in &krate.externs {
             let src_root = match e.src {
-                FileName::Real(ref p) => match p.parent() {
+                FileName::Real(ref p) => match p.local_path().parent() {
                     Some(p) => p.to_path_buf(),
                     None => PathBuf::new(),
                 },
diff --git a/src/librustdoc/html/sources.rs b/src/librustdoc/html/sources.rs
index c5f44baced2e4..018c0e82c4561 100644
--- a/src/librustdoc/html/sources.rs
+++ b/src/librustdoc/html/sources.rs
@@ -67,10 +67,10 @@ impl<'a> SourceCollector<'a> {
     /// Renders the given filename into its corresponding HTML source file.
     fn emit_source(&mut self, filename: &FileName) -> Result<(), Error> {
         let p = match *filename {
-            FileName::Real(ref file) => file,
+            FileName::Real(ref file) => file.local_path().to_path_buf(),
             _ => return Ok(()),
         };
-        if self.scx.local_sources.contains_key(&**p) {
+        if self.scx.local_sources.contains_key(&*p) {
             // We've already emitted this source
             return Ok(());
         }
diff --git a/src/librustdoc/test.rs b/src/librustdoc/test.rs
index 85ba4cbdc7e1b..4b15a591da71f 100644
--- a/src/librustdoc/test.rs
+++ b/src/librustdoc/test.rs
@@ -688,7 +688,7 @@ impl Collector {
             let filename = source_map.span_to_filename(self.position);
             if let FileName::Real(ref filename) = filename {
                 if let Ok(cur_dir) = env::current_dir() {
-                    if let Ok(path) = filename.strip_prefix(&cur_dir) {
+                    if let Ok(path) = filename.local_path().strip_prefix(&cur_dir) {
                         return path.to_owned().into();
                     }
                 }
@@ -718,7 +718,7 @@ impl Tester for Collector {
         // FIXME(#44940): if doctests ever support path remapping, then this filename
         // needs to be the result of `SourceMap::span_to_unmapped_path`.
         let path = match &filename {
-            FileName::Real(path) => path.clone(),
+            FileName::Real(path) => path.local_path().to_path_buf(),
             _ => PathBuf::from(r"doctest.rs"),
         };