Use lib-asan sysroot when ASAN is enabled

This commit also adds a unstable rustc flag to toggle using prebuilt
libraries.
Since we are not yet distributing the prebuilt artifacts, it is currently
set to `no`. Eventually, with cargo and `-Z build-std` we want to
disable using the prebuilt standard libraries (which is why it is should
later be `yes` by default).

Co-authored-by: Eric Holk <ericholk@microsoft.com>

Author: jakos-sec

compiler/rustc_session/src/filesearch.rs

@@ -49,6 +49,11 @@ pub fn make_target_lib_path(sysroot: &Path, target_triple: &str) -> PathBuf {
     sysroot.join(rustlib_path).join("lib")
 }
 
+pub fn make_target_lib_path_with_asan(sysroot: &Path, target_triple: &str) -> PathBuf {
+    let rustlib_path = rustc_target::relative_target_rustlib_path(sysroot, target_triple);
+    sysroot.join(rustlib_path).join("lib-asan")
+}
+
 /// Returns a path to the target's `bin` folder within its `rustlib` path in the sysroot. This is
 /// where binaries are usually installed, e.g. the self-contained linkers, lld-wrappers, LLVM tools,
 /// etc.

compiler/rustc_session/src/options.rs

@@ -2591,6 +2591,8 @@ written to standard error output)"),
         "enable origins tracking in MemorySanitizer"),
     sanitizer_recover: SanitizerSet = (SanitizerSet::empty(), parse_sanitizers, [TRACKED],
         "enable recovery for selected sanitizers"),
+    sanitizer_use_prebuilt_library: bool = (false, parse_bool, [TRACKED],
+        "enable using the prebuilt sanitizer instrumented library artifacts (default: no)"),
     saturating_float_casts: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "make float->int casts UB-free: numbers outside the integer type's range are clipped to \
         the max/min integer respectively, and NaN is mapped to 0 (default: yes)"),

compiler/rustc_session/src/search_paths.rs

@@ -5,7 +5,7 @@ use rustc_macros::{Decodable, Encodable, HashStable_Generic};
 use rustc_target::spec::TargetTuple;
 
 use crate::EarlyDiagCtxt;
-use crate::filesearch::make_target_lib_path;
+use crate::filesearch::{make_target_lib_path, make_target_lib_path_with_asan};
 
 #[derive(Clone, Debug)]
 pub struct SearchPath {
@@ -131,6 +131,10 @@ impl SearchPath {
         Self::new(PathKind::All, make_target_lib_path(sysroot, triple))
     }
 
+    pub fn from_sysroot_and_triple_with_asan(sysroot: &Path, triple: &str) -> Self {
+        Self::new(PathKind::All, make_target_lib_path_with_asan(sysroot, triple))
+    }
+
     pub fn new(kind: PathKind, dir: PathBuf) -> Self {
         // Get the files within the directory.
         let mut files = match std::fs::read_dir(&dir) {

compiler/rustc_session/src/session.rs

@@ -1088,12 +1088,18 @@ pub fn build_session(
     let mut psess = ParseSess::with_dcx(dcx, source_map);
     psess.assume_incomplete_release = sopts.unstable_opts.assume_incomplete_release;
 
+    let asan = sopts.unstable_opts.sanitizer.contains(SanitizerSet::ADDRESS);
+
     let host_triple = config::host_tuple();
     let target_triple = sopts.target_triple.tuple();
     // FIXME use host sysroot?
     let host_tlib_path =
         Arc::new(SearchPath::from_sysroot_and_triple(sopts.sysroot.path(), host_triple));
-    let target_tlib_path = if host_triple == target_triple {
+    let target_tlib_path = if asan && sopts.unstable_opts.sanitizer_use_prebuilt_library {
+        // If ASAN is enabled, we need to use the target lib path with ASAN
+        // enabled, which is different from the host lib path.
+        Arc::new(SearchPath::from_sysroot_and_triple_with_asan(sopts.sysroot.path(), target_triple))
+    } else if host_triple == target_triple {
         // Use the same `SearchPath` if host and target triple are identical to avoid unnecessary
         // rescanning of the target lib path and an unnecessary allocation.
         Arc::clone(&host_tlib_path)