Auto merge of #69718 - arlosi:debughash, r=eddyb

Add hash of source files in debug info

LLVM supports placing the hash of source files inside the debug info.
This information can be used by a debugger to verify that the source code matches
the executable.

This change adds support for both hash algorithms supported by LLVM, MD5 and SHA1, controlled by a target option.

* DWARF only supports MD5
* LLVM IR supports MD5 and SHA1 (and SHA256 in LLVM 11).
* CodeView (.PDB) supports MD5, SHA1, and SHA256.

Fixes #68980.

Tracking issue: #70401

rustc dev guide PR with further details: https://github.com/rust-lang/rustc-dev-guide/pull/623

19 files changed, 332 insertions, 92 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 15d016a97cf..64c60ab7b4e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -88,12 +88,6 @@ dependencies = [
 ]
 
 [[package]]
-name = "arrayref"
-version = "0.3.5"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0d382e583f07208808f6b1249e60848879ba3543f57c32277bf52d69c2f0f0ee"
-
-[[package]]
 name = "arrayvec"
 version = "0.4.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -187,11 +181,22 @@ dependencies = [
 
 [[package]]
 name = "block-buffer"
-version = "0.3.3"
+version = "0.7.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c0940dc441f31689269e10ac70eb1002a3a1d3ad1390e030043662eb7fe4688b"
+dependencies = [
+ "block-padding",
+ "byte-tools",
+ "byteorder",
+ "generic-array",
+]
+
+[[package]]
+name = "block-padding"
+version = "0.1.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a076c298b9ecdb530ed9d967e74a6027d6a7478924520acddcddc24c1c8ab3ab"
+checksum = "fa79dedbb091f449f1f39e53edf88d5dbe95f895dae6135a8d7b881fb5af73f5"
 dependencies = [
- "arrayref",
  "byte-tools",
 ]
 
@@ -240,9 +245,9 @@ version = "0.1.0"
 
 [[package]]
 name = "byte-tools"
-version = "0.2.0"
+version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "560c32574a12a89ecd91f5e742165893f86e3ab98d21f8ea548658eb9eef5f40"
+checksum = "e3b5ca7a04898ad4bcd41c90c5285445ff5b791899bb1b0abdd2a2aa791211d7"
 
 [[package]]
 name = "bytecount"
@@ -897,9 +902,9 @@ checksum = "524cbf6897b527295dff137cec09ecf3a05f4fddffd7dfcd1585403449e74198"
 
 [[package]]
 name = "digest"
-version = "0.7.6"
+version = "0.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "03b072242a8cbaf9c145665af9d250c59af3b958f83ed6824e13533cf76d5b90"
+checksum = "f3d0c8c8752312f9713efd397ff63acb9f85585afbf179282e720e7704954dd5"
 dependencies = [
  "generic-array",
 ]
@@ -1226,9 +1231,9 @@ dependencies = [
 
 [[package]]
 name = "generic-array"
-version = "0.9.0"
+version = "0.12.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ef25c5683767570c2bbd7deba372926a55eaae9982d7726ee2a1050239d45b9d"
+checksum = "c68f0274ae0e023facc3c97b2e00f076be70e254bc851d972503b328db79b2ec"
 dependencies = [
  "typenum",
 ]
@@ -1963,6 +1968,17 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7ffc5c5338469d4d3ea17d269fa8ea3512ad247247c30bd2df69e68309ed0a08"
 
 [[package]]
+name = "md-5"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a18af3dcaf2b0219366cdb4e2af65a6101457b415c3d1a5c71dd9c2b7c77b9c8"
+dependencies = [
+ "block-buffer",
+ "digest",
+ "opaque-debug",
+]
+
+[[package]]
 name = "mdbook"
 version = "0.3.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2251,6 +2267,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d6a04cb71e910d0034815600180f62a95bf6e67942d7ab52a166a68c7d7e9cd0"
 
 [[package]]
+name = "opaque-debug"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2839e79665f131bdb5782e51f2c6c9599c133c6098982a54c794358bf432529c"
+
+[[package]]
 name = "open"
 version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2467,9 +2489,9 @@ dependencies = [
 
 [[package]]
 name = "pest_meta"
-version = "2.1.0"
+version = "2.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f5a3492a4ed208ffc247adcdcc7ba2a95be3104f58877d0d02f0df39bf3efb5e"
+checksum = "54be6e404f5317079812fc8f9f5279de376d8856929e21c184ecf6bbd692a11d"
 dependencies = [
  "maplit",
  "pest",
@@ -4155,11 +4177,13 @@ dependencies = [
  "arena",
  "cfg-if",
  "log",
+ "md-5",
  "rustc_data_structures",
  "rustc_index",
  "rustc_macros",
  "scoped-tls",
  "serialize",
+ "sha-1",
  "unicode-width",
 ]
 
@@ -4535,14 +4559,14 @@ dependencies = [
 
 [[package]]
 name = "sha-1"
-version = "0.7.0"
+version = "0.8.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "51b9d1f3b5de8a167ab06834a7c883bd197f2191e1dda1a22d9ccfeedbf9aded"
+checksum = "f7d94d0bede923b3cea61f3f1ff57ff8cdfd77b400fb8f9998949e0cf04163df"
 dependencies = [
  "block-buffer",
- "byte-tools",
  "digest",
  "fake-simd",
+ "opaque-debug",
 ]
 
 [[package]]
diff --git a/src/doc/unstable-book/src/compiler-flags/src-hash-algorithm.md b/src/doc/unstable-book/src/compiler-flags/src-hash-algorithm.md
new file mode 100644
index 00000000000..5a7d0655a44
--- /dev/null
+++ b/src/doc/unstable-book/src/compiler-flags/src-hash-algorithm.md
@@ -0,0 +1,11 @@
+# `src-hash-algorithm`
+
+The tracking issue for this feature is: [#70401](https://github.com/rust-lang/rust/issues/70401).
+
+------------------------
+
+The `-Z src-hash-algorithm` compiler flag controls which algorithm is used when hashing each source file. The hash is stored in the debug info and can be used by a debugger to verify the source code matches the executable.
+
+Supported hash algorithms are: `md5`, and `sha1`. Note that not all hash algorithms are supported by all debug info formats.
+
+By default, the compiler chooses the hash algorithm based on the target specification.
diff --git a/src/librustc_codegen_llvm/debuginfo/metadata.rs b/src/librustc_codegen_llvm/debuginfo/metadata.rs
index a9e21c056a3..700f25d35bc 100644
--- a/src/librustc_codegen_llvm/debuginfo/metadata.rs
+++ b/src/librustc_codegen_llvm/debuginfo/metadata.rs
@@ -41,7 +41,7 @@ use rustc_middle::ty::{self, AdtKind, ParamEnv, Ty, TyCtxt};
 use rustc_middle::{bug, span_bug};
 use rustc_session::config::{self, DebugInfo};
 use rustc_span::symbol::{Interner, Symbol};
-use rustc_span::{self, FileName, Span};
+use rustc_span::{self, FileName, SourceFileHash, Span};
 use rustc_target::abi::{Abi, Align, DiscriminantKind, HasDataLayout, Integer, LayoutOf};
 use rustc_target::abi::{Int, Pointer, F32, F64};
 use rustc_target::abi::{Primitive, Size, VariantIdx, Variants};
@@ -751,6 +751,14 @@ pub fn type_metadata(cx: &CodegenCx<'ll, 'tcx>, t: Ty<'tcx>, usage_site_span: Sp
     metadata
 }
 
+fn hex_encode(data: &[u8]) -> String {
+    let mut hex_string = String::with_capacity(data.len() * 2);
+    for byte in data.iter() {
+        write!(&mut hex_string, "{:02x}", byte).unwrap();
+    }
+    hex_string
+}
+
 pub fn file_metadata(
     cx: &CodegenCx<'ll, '_>,
     file_name: &FileName,
@@ -758,6 +766,8 @@ pub fn file_metadata(
 ) -> &'ll DIFile {
     debug!("file_metadata: file_name: {}, defining_crate: {}", file_name, defining_crate);
 
+    let source_file = cx.sess().source_map().get_source_file(file_name);
+    let hash = source_file.as_ref().map(|f| &f.src_hash);
     let file_name = Some(file_name.to_string());
     let directory = if defining_crate == LOCAL_CRATE {
         Some(cx.sess().working_dir.0.to_string_lossy().to_string())
@@ -766,17 +776,18 @@ pub fn file_metadata(
         // independent of the compiler's working directory one way or another.
         None
     };
-    file_metadata_raw(cx, file_name, directory)
+    file_metadata_raw(cx, file_name, directory, hash)
 }
 
 pub fn unknown_file_metadata(cx: &CodegenCx<'ll, '_>) -> &'ll DIFile {
-    file_metadata_raw(cx, None, None)
+    file_metadata_raw(cx, None, None, None)
 }
 
 fn file_metadata_raw(
     cx: &CodegenCx<'ll, '_>,
     file_name: Option<String>,
     directory: Option<String>,
+    hash: Option<&SourceFileHash>,
 ) -> &'ll DIFile {
     let key = (file_name, directory);
 
@@ -789,6 +800,17 @@ fn file_metadata_raw(
             let file_name = file_name.as_deref().unwrap_or("<unknown>");
             let directory = directory.as_deref().unwrap_or("");
 
+            let (hash_kind, hash_value) = match hash {
+                Some(hash) => {
+                    let kind = match hash.kind {
+                        rustc_span::SourceFileHashAlgorithm::Md5 => llvm::ChecksumKind::MD5,
+                        rustc_span::SourceFileHashAlgorithm::Sha1 => llvm::ChecksumKind::SHA1,
+                    };
+                    (kind, hex_encode(hash.hash_bytes()))
+                }
+                None => (llvm::ChecksumKind::None, String::new()),
+            };
+
             let file_metadata = unsafe {
                 llvm::LLVMRustDIBuilderCreateFile(
                     DIB(cx),
@@ -796,6 +818,9 @@ fn file_metadata_raw(
                     file_name.len(),
                     directory.as_ptr().cast(),
                     directory.len(),
+                    hash_kind,
+                    hash_value.as_ptr().cast(),
+                    hash_value.len(),
                 )
             };
 
@@ -920,6 +945,9 @@ pub fn compile_unit_metadata(
             name_in_debuginfo.len(),
             work_dir.as_ptr().cast(),
             work_dir.len(),
+            llvm::ChecksumKind::None,
+            ptr::null(),
+            0,
         );
 
         let unit_metadata = llvm::LLVMRustDIBuilderCreateCompileUnit(
diff --git a/src/librustc_codegen_llvm/llvm/ffi.rs b/src/librustc_codegen_llvm/llvm/ffi.rs
index 1d61d95cc6b..aeb34e5c9c9 100644
--- a/src/librustc_codegen_llvm/llvm/ffi.rs
+++ b/src/librustc_codegen_llvm/llvm/ffi.rs
@@ -546,6 +546,15 @@ pub enum ThreadLocalMode {
     LocalExec,
 }
 
+/// LLVMRustChecksumKind
+#[derive(Copy, Clone)]
+#[repr(C)]
+pub enum ChecksumKind {
+    None,
+    MD5,
+    SHA1,
+}
+
 extern "C" {
     type Opaque;
 }
@@ -1640,6 +1649,9 @@ extern "C" {
         FilenameLen: size_t,
         Directory: *const c_char,
         DirectoryLen: size_t,
+        CSKind: ChecksumKind,
+        Checksum: *const c_char,
+        ChecksumLen: size_t,
     ) -> &'a DIFile;
 
     pub fn LLVMRustDIBuilderCreateSubroutineType(
diff --git a/src/librustc_interface/util.rs b/src/librustc_interface/util.rs
index a8cc34e1854..02bf1aded3b 100644
--- a/src/librustc_interface/util.rs
+++ b/src/librustc_interface/util.rs
@@ -22,7 +22,7 @@ use rustc_session::parse::CrateConfig;
 use rustc_session::CrateDisambiguator;
 use rustc_session::{config, early_error, filesearch, output, DiagnosticOutput, Session};
 use rustc_span::edition::Edition;
-use rustc_span::source_map::{FileLoader, RealFileLoader, SourceMap};
+use rustc_span::source_map::{FileLoader, SourceMap};
 use rustc_span::symbol::{sym, Symbol};
 use smallvec::SmallVec;
 use std::env;
@@ -62,15 +62,13 @@ pub fn create_session(
     lint_caps: FxHashMap<lint::LintId, lint::Level>,
     descriptions: Registry,
 ) -> (Lrc<Session>, Lrc<Box<dyn CodegenBackend>>, Lrc<SourceMap>) {
-    let loader = file_loader.unwrap_or(box RealFileLoader);
-    let source_map = Lrc::new(SourceMap::with_file_loader(loader, sopts.file_path_mapping()));
-    let mut sess = session::build_session_with_source_map(
+    let (mut sess, source_map) = session::build_session_with_source_map(
         sopts,
         input_path,
         descriptions,
-        source_map.clone(),
         diagnostic_output,
         lint_caps,
+        file_loader,
     );
 
     let codegen_backend = get_codegen_backend(&sess);
diff --git a/src/librustc_middle/ich/impls_syntax.rs b/src/librustc_middle/ich/impls_syntax.rs
index c5a4b53b10d..300aac19e51 100644
--- a/src/librustc_middle/ich/impls_syntax.rs
+++ b/src/librustc_middle/ich/impls_syntax.rs
@@ -61,7 +61,7 @@ impl<'a> HashStable<StableHashingContext<'a>> for SourceFile {
             cnum,
             // Do not hash the source as it is not encoded
             src: _,
-            src_hash,
+            ref src_hash,
             external_src: _,
             start_pos,
             end_pos: _,
diff --git a/src/librustc_session/config.rs b/src/librustc_session/config.rs
index 54481bd124d..58a03dbe388 100644
--- a/src/librustc_session/config.rs
+++ b/src/librustc_session/config.rs
@@ -18,9 +18,10 @@ use rustc_feature::UnstableFeatures;
 use rustc_span::edition::{Edition, DEFAULT_EDITION, EDITION_NAME_LIST};
 use rustc_span::source_map::{FileName, FilePathMapping};
 use rustc_span::symbol::{sym, Symbol};
+use rustc_span::SourceFileHashAlgorithm;
 
 use rustc_errors::emitter::HumanReadableErrorType;
-use rustc_errors::{ColorConfig, FatalError, Handler, HandlerFlags};
+use rustc_errors::{ColorConfig, HandlerFlags};
 
 use std::collections::btree_map::{
     Iter as BTreeMapIter, Keys as BTreeMapKeysIter, Values as BTreeMapValuesIter,
@@ -748,25 +749,30 @@ pub fn build_configuration(sess: &Session, mut user_cfg: CrateConfig) -> CrateCo
     user_cfg
 }
 
-pub fn build_target_config(opts: &Options, sp: &Handler) -> Config {
+pub fn build_target_config(opts: &Options, error_format: ErrorOutputType) -> Config {
     let target = Target::search(&opts.target_triple).unwrap_or_else(|e| {
-        sp.struct_fatal(&format!("Error loading target specification: {}", e))
-            .help("Use `--print target-list` for a list of built-in targets")
-            .emit();
-        FatalError.raise();
+        early_error(
+            error_format,
+            &format!(
+                "Error loading target specification: {}. \
+            Use `--print target-list` for a list of built-in targets",
+                e
+            ),
+        )
     });
 
     let ptr_width = match &target.target_pointer_width[..] {
         "16" => 16,
         "32" => 32,
         "64" => 64,
-        w => sp
-            .fatal(&format!(
+        w => early_error(
+            error_format,
+            &format!(
                 "target specification was invalid: \
              unrecognized target-pointer-width {}",
                 w
-            ))
-            .raise(),
+            ),
+        ),
     };
 
     Config { target, ptr_width }
@@ -1971,7 +1977,8 @@ impl PpMode {
 crate mod dep_tracking {
     use super::{
         CFGuard, CrateType, DebugInfo, ErrorOutputType, LinkerPluginLto, LtoCli, OptLevel,
-        OutputTypes, Passes, Sanitizer, SwitchWithOptPath, SymbolManglingVersion,
+        OutputTypes, Passes, Sanitizer, SourceFileHashAlgorithm, SwitchWithOptPath,
+        SymbolManglingVersion,
     };
     use crate::lint;
     use crate::utils::NativeLibraryKind;
@@ -2049,6 +2056,7 @@ crate mod dep_tracking {
     impl_dep_tracking_hash_via_hash!(LinkerPluginLto);
     impl_dep_tracking_hash_via_hash!(SwitchWithOptPath);
     impl_dep_tracking_hash_via_hash!(SymbolManglingVersion);
+    impl_dep_tracking_hash_via_hash!(Option<SourceFileHashAlgorithm>);
 
     impl_dep_tracking_hash_for_sortable_vec_of!(String);
     impl_dep_tracking_hash_for_sortable_vec_of!(PathBuf);
diff --git a/src/librustc_session/options.rs b/src/librustc_session/options.rs
index 432f1e17ab3..3962e30335d 100644
--- a/src/librustc_session/options.rs
+++ b/src/librustc_session/options.rs
@@ -10,6 +10,7 @@ use rustc_target::spec::{LinkerFlavor, MergeFunctions, PanicStrategy, RelroLevel
 
 use rustc_feature::UnstableFeatures;
 use rustc_span::edition::Edition;
+use rustc_span::SourceFileHashAlgorithm;
 
 use std::collections::BTreeMap;
 
@@ -283,12 +284,14 @@ macro_rules! options {
             Some("one of: `disabled`, `trampolines`, or `aliases`");
         pub const parse_symbol_mangling_version: Option<&str> =
             Some("either `legacy` or `v0` (RFC 2603)");
+        pub const parse_src_file_hash: Option<&str> =
+            Some("either `md5`, or `sha1`");
     }
 
     #[allow(dead_code)]
     mod $mod_set {
         use super::{$struct_name, Passes, Sanitizer, LtoCli, LinkerPluginLto, SwitchWithOptPath,
-            SymbolManglingVersion, CFGuard};
+            SymbolManglingVersion, CFGuard, SourceFileHashAlgorithm};
         use rustc_target::spec::{LinkerFlavor, MergeFunctions, PanicStrategy, RelroLevel};
         use std::path::PathBuf;
         use std::str::FromStr;
@@ -622,6 +625,14 @@ macro_rules! options {
             };
             true
         }
+
+        fn parse_src_file_hash(slot: &mut Option<SourceFileHashAlgorithm>, v: Option<&str>) -> bool {
+            match v.and_then(|s| SourceFileHashAlgorithm::from_str(s).ok()) {
+                Some(hash_kind) => *slot = Some(hash_kind),
+                _ => return false,
+            }
+            true
+        }
     }
 ) }
 
@@ -961,4 +972,6 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "use new LLVM pass manager"),
     link_native_libraries: Option<bool> = (None, parse_opt_bool, [UNTRACKED],
         "Link native libraries in the linker invocation."),
+    src_hash_algorithm: Option<SourceFileHashAlgorithm> = (None, parse_src_file_hash, [TRACKED],
+        "hash algorithm of source files in debug info (`md5`, or `sha1`)"),
 }
diff --git a/src/librustc_session/session.rs b/src/librustc_session/session.rs
index 98d0fa74d62..1c5d19db49c 100644
--- a/src/librustc_session/session.rs
+++ b/src/librustc_session/session.rs
@@ -20,7 +20,8 @@ use rustc_errors::emitter::{Emitter, EmitterWriter, HumanReadableErrorType};
 use rustc_errors::json::JsonEmitter;
 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticId, ErrorReported};
 use rustc_span::edition::Edition;
-use rustc_span::source_map::{self, MultiSpan, Span};
+use rustc_span::source_map::{self, FileLoader, MultiSpan, RealFileLoader, SourceMap, Span};
+use rustc_span::SourceFileHashAlgorithm;
 use rustc_target::spec::{PanicStrategy, RelroLevel, Target, TargetTriple};
 
 use std::cell::{self, RefCell};
@@ -870,16 +871,15 @@ pub fn build_session(
     local_crate_source_file: Option<PathBuf>,
     registry: rustc_errors::registry::Registry,
 ) -> Session {
-    let file_path_mapping = sopts.file_path_mapping();
-
     build_session_with_source_map(
         sopts,
         local_crate_source_file,
         registry,
-        Lrc::new(source_map::SourceMap::new(file_path_mapping)),
         DiagnosticOutput::Default,
         Default::default(),
+        None,
     )
+    .0
 }
 
 fn default_emitter(
@@ -956,10 +956,10 @@ pub fn build_session_with_source_map(
     sopts: config::Options,
     local_crate_source_file: Option<PathBuf>,
     registry: rustc_errors::registry::Registry,
-    source_map: Lrc<source_map::SourceMap>,
     diagnostics_output: DiagnosticOutput,
-    lint_caps: FxHashMap<lint::LintId, lint::Level>,
-) -> Session {
+    driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
+    file_loader: Option<Box<dyn FileLoader + Send + Sync + 'static>>,
+) -> (Session, Lrc<SourceMap>) {
     // FIXME: This is not general enough to make the warning lint completely override
     // normal diagnostic warnings, since the warning lint can also be denied and changed
     // later via the source code.
@@ -977,23 +977,33 @@ pub fn build_session_with_source_map(
         DiagnosticOutput::Default => None,
         DiagnosticOutput::Raw(write) => Some(write),
     };
+
+    let target_cfg = config::build_target_config(&sopts, sopts.error_format);
+    let host_triple = TargetTriple::from_triple(config::host_triple());
+    let host = Target::search(&host_triple).unwrap_or_else(|e| {
+        early_error(sopts.error_format, &format!("Error loading host specification: {}", e))
+    });
+
+    let loader = file_loader.unwrap_or(Box::new(RealFileLoader));
+    let hash_kind = sopts.debugging_opts.src_hash_algorithm.unwrap_or_else(|| {
+        if target_cfg.target.options.is_like_msvc {
+            SourceFileHashAlgorithm::Sha1
+        } else {
+            SourceFileHashAlgorithm::Md5
+        }
+    });
+    let source_map = Lrc::new(SourceMap::with_file_loader_and_hash_kind(
+        loader,
+        sopts.file_path_mapping(),
+        hash_kind,
+    ));
     let emitter = default_emitter(&sopts, registry, &source_map, write_dest);
 
-    let diagnostic_handler = rustc_errors::Handler::with_emitter_and_flags(
+    let span_diagnostic = rustc_errors::Handler::with_emitter_and_flags(
         emitter,
         sopts.debugging_opts.diagnostic_handler_flags(can_emit_warnings),
     );
 
-    build_session_(sopts, local_crate_source_file, diagnostic_handler, source_map, lint_caps)
-}
-
-fn build_session_(
-    sopts: config::Options,
-    local_crate_source_file: Option<PathBuf>,
-    span_diagnostic: rustc_errors::Handler,
-    source_map: Lrc<source_map::SourceMap>,
-    driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
-) -> Session {
     let self_profiler = if let SwitchWithOptPath::Enabled(ref d) = sopts.debugging_opts.self_profile
     {
         let directory =
@@ -1015,13 +1025,7 @@ fn build_session_(
         None
     };
 
-    let host_triple = TargetTriple::from_triple(config::host_triple());
-    let host = Target::search(&host_triple).unwrap_or_else(|e| {
-        span_diagnostic.fatal(&format!("Error loading host specification: {}", e)).raise()
-    });
-    let target_cfg = config::build_target_config(&sopts, &span_diagnostic);
-
-    let parse_sess = ParseSess::with_span_handler(span_diagnostic, source_map);
+    let parse_sess = ParseSess::with_span_handler(span_diagnostic, source_map.clone());
     let sysroot = match &sopts.maybe_sysroot {
         Some(sysroot) => sysroot.clone(),
         None => filesearch::get_or_default_sysroot(),
@@ -1135,7 +1139,7 @@ fn build_session_(
 
     validate_commandline_args_with_session_available(&sess);
 
-    sess
+    (sess, source_map)
 }
 
 // If it is useful to have a Session available already for validating a
diff --git a/src/librustc_span/Cargo.toml b/src/librustc_span/Cargo.toml
index c3fa2331d2b..1c2721260d6 100644
--- a/src/librustc_span/Cargo.toml
+++ b/src/librustc_span/Cargo.toml
@@ -19,3 +19,5 @@ scoped-tls = "1.0"
 unicode-width = "0.1.4"
 cfg-if = "0.1.2"
 log = "0.4"
+sha-1 = "0.8"
+md-5 = "0.8"
diff --git a/src/librustc_span/lib.rs b/src/librustc_span/lib.rs
index 3bcc20d36e7..0d9f3f214fb 100644
--- a/src/librustc_span/lib.rs
+++ b/src/librustc_span/lib.rs
@@ -47,9 +47,14 @@ use std::borrow::Cow;
 use std::cell::RefCell;
 use std::cmp::{self, Ordering};
 use std::fmt;
-use std::hash::{Hash, Hasher};
+use std::hash::Hash;
 use std::ops::{Add, Sub};
 use std::path::PathBuf;
+use std::str::FromStr;
+
+use md5::Md5;
+use sha1::Digest;
+use sha1::Sha1;
 
 #[cfg(test)]
 mod tests;
@@ -874,6 +879,70 @@ impl ExternalSource {
 #[derive(Debug)]
 pub struct OffsetOverflowError;
 
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, RustcEncodable, RustcDecodable)]
+pub enum SourceFileHashAlgorithm {
+    Md5,
+    Sha1,
+}
+
+impl FromStr for SourceFileHashAlgorithm {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<SourceFileHashAlgorithm, ()> {
+        match s {
+            "md5" => Ok(SourceFileHashAlgorithm::Md5),
+            "sha1" => Ok(SourceFileHashAlgorithm::Sha1),
+            _ => Err(()),
+        }
+    }
+}
+
+rustc_data_structures::impl_stable_hash_via_hash!(SourceFileHashAlgorithm);
+
+/// The hash of the on-disk source file used for debug info.
+#[derive(Copy, Clone, PartialEq, Eq, Debug, RustcEncodable, RustcDecodable)]
+#[derive(HashStable_Generic)]
+pub struct SourceFileHash {
+    pub kind: SourceFileHashAlgorithm,
+    value: [u8; 20],
+}
+
+impl SourceFileHash {
+    pub fn new(kind: SourceFileHashAlgorithm, src: &str) -> SourceFileHash {
+        let mut hash = SourceFileHash { kind, value: Default::default() };
+        let len = hash.hash_len();
+        let value = &mut hash.value[..len];
+        let data = src.as_bytes();
+        match kind {
+            SourceFileHashAlgorithm::Md5 => {
+                value.copy_from_slice(&Md5::digest(data));
+            }
+            SourceFileHashAlgorithm::Sha1 => {
+                value.copy_from_slice(&Sha1::digest(data));
+            }
+        }
+        hash
+    }
+
+    /// Check if the stored hash matches the hash of the string.
+    pub fn matches(&self, src: &str) -> bool {
+        Self::new(self.kind, src) == *self
+    }
+
+    /// The bytes of the hash.
+    pub fn hash_bytes(&self) -> &[u8] {
+        let len = self.hash_len();
+        &self.value[..len]
+    }
+
+    fn hash_len(&self) -> usize {
+        match self.kind {
+            SourceFileHashAlgorithm::Md5 => 16,
+            SourceFileHashAlgorithm::Sha1 => 20,
+        }
+    }
+}
+
 /// A single source in the `SourceMap`.
 #[derive(Clone)]
 pub struct SourceFile {
@@ -889,7 +958,7 @@ pub struct SourceFile {
     /// The complete source code.
     pub src: Option<Lrc<String>>,
     /// The source code's hash.
-    pub src_hash: u128,
+    pub src_hash: SourceFileHash,
     /// The external source code (used for external crates, which will have a `None`
     /// value as `self.src`.
     pub external_src: Lock<ExternalSource>,
@@ -987,7 +1056,8 @@ impl Decodable for SourceFile {
             let name: FileName = d.read_struct_field("name", 0, |d| Decodable::decode(d))?;
             let name_was_remapped: bool =
                 d.read_struct_field("name_was_remapped", 1, |d| Decodable::decode(d))?;
-            let src_hash: u128 = d.read_struct_field("src_hash", 2, |d| Decodable::decode(d))?;
+            let src_hash: SourceFileHash =
+                d.read_struct_field("src_hash", 2, |d| Decodable::decode(d))?;
             let start_pos: BytePos =
                 d.read_struct_field("start_pos", 3, |d| Decodable::decode(d))?;
             let end_pos: BytePos = d.read_struct_field("end_pos", 4, |d| Decodable::decode(d))?;
@@ -1062,14 +1132,12 @@ impl SourceFile {
         unmapped_path: FileName,
         mut src: String,
         start_pos: BytePos,
+        hash_kind: SourceFileHashAlgorithm,
     ) -> Self {
+        // Compute the file hash before any normalization.
+        let src_hash = SourceFileHash::new(hash_kind, &src);
         let normalized_pos = normalize_src(&mut src, start_pos);
 
-        let src_hash = {
-            let mut hasher: StableHasher = StableHasher::new();
-            hasher.write(src.as_bytes());
-            hasher.finish::<u128>()
-        };
         let name_hash = {
             let mut hasher: StableHasher = StableHasher::new();
             name.hash(&mut hasher);
@@ -1125,10 +1193,7 @@ impl SourceFile {
             } = &mut *external_src
             {
                 if let Some(src) = src {
-                    let mut hasher: StableHasher = StableHasher::new();
-                    hasher.write(src.as_bytes());
-
-                    if hasher.finish::<u128>() == self.src_hash {
+                    if self.src_hash.matches(&src) {
                         *src_kind = ExternalSourceKind::Present(Lrc::new(src));
                         return true;
                     }
diff --git a/src/librustc_span/source_map.rs b/src/librustc_span/source_map.rs
index 57e68320f3f..49e2144b3e3 100644
--- a/src/librustc_span/source_map.rs
+++ b/src/librustc_span/source_map.rs
@@ -141,27 +141,31 @@ pub struct SourceMap {
     // This is used to apply the file path remapping as specified via
     // `--remap-path-prefix` to all `SourceFile`s allocated within this `SourceMap`.
     path_mapping: FilePathMapping,
+
+    /// The algorithm used for hashing the contents of each source file.
+    hash_kind: SourceFileHashAlgorithm,
 }
 
 impl SourceMap {
     pub fn new(path_mapping: FilePathMapping) -> SourceMap {
-        SourceMap {
-            used_address_space: AtomicU32::new(0),
-            files: Default::default(),
-            file_loader: Box::new(RealFileLoader),
+        Self::with_file_loader_and_hash_kind(
+            Box::new(RealFileLoader),
             path_mapping,
-        }
+            SourceFileHashAlgorithm::Md5,
+        )
     }
 
-    pub fn with_file_loader(
+    pub fn with_file_loader_and_hash_kind(
         file_loader: Box<dyn FileLoader + Sync + Send>,
         path_mapping: FilePathMapping,
+        hash_kind: SourceFileHashAlgorithm,
     ) -> SourceMap {
         SourceMap {
             used_address_space: AtomicU32::new(0),
             files: Default::default(),
             file_loader,
             path_mapping,
+            hash_kind,
         }
     }
 
@@ -275,6 +279,7 @@ impl SourceMap {
                     unmapped_path,
                     src,
                     Pos::from_usize(start_pos),
+                    self.hash_kind,
                 ));
 
                 let mut files = self.files.borrow_mut();
@@ -296,7 +301,7 @@ impl SourceMap {
         &self,
         filename: FileName,
         name_was_remapped: bool,
-        src_hash: u128,
+        src_hash: SourceFileHash,
         name_hash: u128,
         source_len: usize,
         cnum: CrateNum,
diff --git a/src/libserialize/serialize.rs b/src/libserialize/serialize.rs
index 8c6548cd3c5..e80d16bb0c7 100644
--- a/src/libserialize/serialize.rs
+++ b/src/libserialize/serialize.rs
@@ -706,6 +706,30 @@ impl<T: Decodable> Decodable for Vec<T> {
     }
 }
 
+impl Encodable for [u8; 20] {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_seq(self.len(), |s| {
+            for (i, e) in self.iter().enumerate() {
+                s.emit_seq_elt(i, |s| e.encode(s))?
+            }
+            Ok(())
+        })
+    }
+}
+
+impl Decodable for [u8; 20] {
+    fn decode<D: Decoder>(d: &mut D) -> Result<[u8; 20], D::Error> {
+        d.read_seq(|d, len| {
+            assert!(len == 20);
+            let mut v = [0u8; 20];
+            for i in 0..len {
+                v[i] = d.read_seq_elt(i, |d| Decodable::decode(d))?;
+            }
+            Ok(v)
+        })
+    }
+}
+
 impl<'a, T: Encodable> Encodable for Cow<'a, [T]>
 where
     [T]: ToOwned<Owned = Vec<T>>,
diff --git a/src/rustllvm/RustWrapper.cpp b/src/rustllvm/RustWrapper.cpp
index 799adb41882..21094b32520 100644
--- a/src/rustllvm/RustWrapper.cpp
+++ b/src/rustllvm/RustWrapper.cpp
@@ -640,6 +640,25 @@ static DICompileUnit::DebugEmissionKind fromRust(LLVMRustDebugEmissionKind Kind)
   }
 }
 
+enum class LLVMRustChecksumKind {
+  None,
+  MD5,
+  SHA1,
+};
+
+static Optional<DIFile::ChecksumKind> fromRust(LLVMRustChecksumKind Kind) {
+  switch (Kind) {
+  case LLVMRustChecksumKind::None:
+    return None;
+  case LLVMRustChecksumKind::MD5:
+    return DIFile::ChecksumKind::CSK_MD5;
+  case LLVMRustChecksumKind::SHA1:
+    return DIFile::ChecksumKind::CSK_SHA1;
+  default:
+    report_fatal_error("bad ChecksumKind.");
+  }
+}
+
 extern "C" uint32_t LLVMRustDebugMetadataVersion() {
   return DEBUG_METADATA_VERSION;
 }
@@ -686,9 +705,15 @@ extern "C" LLVMMetadataRef LLVMRustDIBuilderCreateCompileUnit(
 extern "C" LLVMMetadataRef LLVMRustDIBuilderCreateFile(
     LLVMRustDIBuilderRef Builder,
     const char *Filename, size_t FilenameLen,
-    const char *Directory, size_t DirectoryLen) {
+    const char *Directory, size_t DirectoryLen, LLVMRustChecksumKind CSKind,
+    const char *Checksum, size_t ChecksumLen) {
+  Optional<DIFile::ChecksumKind> llvmCSKind = fromRust(CSKind);
+  Optional<DIFile::ChecksumInfo<StringRef>> CSInfo{};
+  if (llvmCSKind)
+    CSInfo.emplace(*llvmCSKind, StringRef{Checksum, ChecksumLen});
   return wrap(Builder->createFile(StringRef(Filename, FilenameLen),
-                                  StringRef(Directory, DirectoryLen)));
+                                  StringRef(Directory, DirectoryLen),
+                                  CSInfo));
 }
 
 extern "C" LLVMMetadataRef
diff --git a/src/test/codegen/remap_path_prefix/main.rs b/src/test/codegen/remap_path_prefix/main.rs
index 4724dc3c3e5..20475bab0fc 100644
--- a/src/test/codegen/remap_path_prefix/main.rs
+++ b/src/test/codegen/remap_path_prefix/main.rs
@@ -22,7 +22,7 @@ fn main() {
 }
 
 // Here we check that local debuginfo is mapped correctly.
-// CHECK: !DIFile(filename: "/the/src/remap_path_prefix/main.rs", directory: "/the/cwd/")
+// CHECK: !DIFile(filename: "/the/src/remap_path_prefix/main.rs", directory: "/the/cwd/"
 
 // And here that debuginfo from other crates are expanded to absolute paths.
-// CHECK: !DIFile(filename: "/the/aux-src/remap_path_prefix_aux.rs", directory: "")
+// CHECK: !DIFile(filename: "/the/aux-src/remap_path_prefix_aux.rs", directory: ""
diff --git a/src/test/codegen/remap_path_prefix/xcrate-generic.rs b/src/test/codegen/remap_path_prefix/xcrate-generic.rs
index 30d6112fd02..7a9d2ca9b6b 100644
--- a/src/test/codegen/remap_path_prefix/xcrate-generic.rs
+++ b/src/test/codegen/remap_path_prefix/xcrate-generic.rs
@@ -11,4 +11,4 @@ pub fn foo() {
 }
 
 // Here we check that local debuginfo is mapped correctly.
-// CHECK: !DIFile(filename: "/the/aux-src/xcrate-generic.rs", directory: "")
+// CHECK: !DIFile(filename: "/the/aux-src/xcrate-generic.rs", directory: ""
diff --git a/src/test/codegen/src-hash-algorithm/src-hash-algorithm-md5.rs b/src/test/codegen/src-hash-algorithm/src-hash-algorithm-md5.rs
new file mode 100644
index 00000000000..64be1127786
--- /dev/null
+++ b/src/test/codegen/src-hash-algorithm/src-hash-algorithm-md5.rs
@@ -0,0 +1,6 @@
+// compile-flags: -g -Z src-hash-algorithm=md5
+
+#![crate_type = "lib"]
+
+pub fn test() {}
+// CHECK: checksumkind: CSK_MD5
diff --git a/src/test/codegen/src-hash-algorithm/src-hash-algorithm-sha1.rs b/src/test/codegen/src-hash-algorithm/src-hash-algorithm-sha1.rs
new file mode 100644
index 00000000000..54e07152142
--- /dev/null
+++ b/src/test/codegen/src-hash-algorithm/src-hash-algorithm-sha1.rs
@@ -0,0 +1,6 @@
+// compile-flags: -g -Z src-hash-algorithm=sha1
+
+#![crate_type = "lib"]
+
+pub fn test() {}
+// CHECK: checksumkind: CSK_SHA1
diff --git a/src/tools/tidy/src/deps.rs b/src/tools/tidy/src/deps.rs
index a221184fab0..62dc965b55f 100644
--- a/src/tools/tidy/src/deps.rs
+++ b/src/tools/tidy/src/deps.rs
@@ -26,7 +26,6 @@ const LICENSES: &[&str] = &[
 const EXCEPTIONS: &[(&str, &str)] = &[
     ("mdbook", "MPL-2.0"),                  // mdbook
     ("openssl", "Apache-2.0"),              // cargo, mdbook
-    ("arrayref", "BSD-2-Clause"),           // mdbook via handlebars via pest
     ("toml-query", "MPL-2.0"),              // mdbook
     ("toml-query_derive", "MPL-2.0"),       // mdbook
     ("is-match", "MPL-2.0"),                // mdbook
@@ -74,6 +73,9 @@ const WHITELIST: &[&str] = &[
     "backtrace",
     "backtrace-sys",
     "bitflags",
+    "block-buffer",
+    "block-padding",
+    "byte-tools",
     "byteorder",
     "c2-chacha",
     "cc",
@@ -87,15 +89,18 @@ const WHITELIST: &[&str] = &[
     "crossbeam-queue",
     "crossbeam-utils",
     "datafrog",
+    "digest",
     "dlmalloc",
     "either",
     "ena",
     "env_logger",
+    "fake-simd",
     "filetime",
     "flate2",
     "fortanix-sgx-abi",
     "fuchsia-zircon",
     "fuchsia-zircon-sys",
+    "generic-array",
     "getopts",
     "getrandom",
     "hashbrown",
@@ -111,6 +116,7 @@ const WHITELIST: &[&str] = &[
     "lock_api",
     "log",
     "log_settings",
+    "md-5",
     "measureme",
     "memchr",
     "memmap",
@@ -118,6 +124,7 @@ const WHITELIST: &[&str] = &[
     "miniz_oxide",
     "nodrop",
     "num_cpus",
+    "opaque-debug",
     "parking_lot",
     "parking_lot_core",
     "pkg-config",
@@ -150,6 +157,7 @@ const WHITELIST: &[&str] = &[
     "semver-parser",
     "serde",
     "serde_derive",
+    "sha-1",
     "smallvec",
     "stable_deref_trait",
     "syn",
@@ -159,6 +167,7 @@ const WHITELIST: &[&str] = &[
     "termion",
     "termize",
     "thread_local",
+    "typenum",
     "ucd-util",
     "unicode-normalization",
     "unicode-script",