Add default sanitizers to TargetOptions

compiler/rustc_session/src/session.rs

@@ -1112,6 +1112,8 @@ pub fn build_session(
 
     let timings = TimingSectionHandler::new(sopts.json_timings);
 
+    let sopts = enable_default_sanitizers(sopts, &target);
+
     let sess = Session {
         target,
         host,
@@ -1143,6 +1145,16 @@ pub fn build_session(
     sess
 }
 
+/// Update parsed sanitizers with the target defaults.
+//
+// This is the first time we have access to both the target and parsed options,
+// and we need to update the sanitizer list for ABI changing sanitizers, like
+// Shadow Call Stack.
+fn enable_default_sanitizers(mut sopts: config::Options, target: &Target) -> config::Options {
+    sopts.unstable_opts.sanitizer |= target.options.default_sanitizers;
+    return sopts;
+}
+
 /// Validate command line arguments with a `Session`.
 ///
 /// If it is useful to have a Session available already for validating a commandline argument, you

compiler/rustc_target/src/spec/json.rs

@@ -214,6 +214,11 @@ impl Target {
                 supported_sanitizers.into_iter().fold(SanitizerSet::empty(), |a, b| a | b);
         }
 
+        if let Some(default_sanitizers) = json.default_sanitizers {
+            base.default_sanitizers =
+                default_sanitizers.into_iter().fold(SanitizerSet::empty(), |a, b| a | b);
+        }
+
         forward!(generate_arange_section);
         forward!(supports_stack_protector);
         forward!(small_data_threshold_support);
@@ -392,6 +397,7 @@ impl ToJson for Target {
         target_option_val!(split_debuginfo);
         target_option_val!(supported_split_debuginfo);
         target_option_val!(supported_sanitizers);
+        target_option_val!(default_sanitizers);
         target_option_val!(c_enum_min_bits);
         target_option_val!(generate_arange_section);
         target_option_val!(supports_stack_protector);
@@ -612,6 +618,7 @@ struct TargetSpecJson {
     split_debuginfo: Option<SplitDebuginfo>,
     supported_split_debuginfo: Option<StaticCow<[SplitDebuginfo]>>,
     supported_sanitizers: Option<Vec<SanitizerSet>>,
+    default_sanitizers: Option<Vec<SanitizerSet>>,
     generate_arange_section: Option<bool>,
     supports_stack_protector: Option<bool>,
     small_data_threshold_support: Option<SmallDataThresholdSupport>,

compiler/rustc_target/src/spec/mod.rs

@@ -2319,6 +2319,13 @@ pub struct TargetOptions {
     /// distributed with the target, the sanitizer should still appear in this list for the target.
     pub supported_sanitizers: SanitizerSet,
 
+    /// The sanitizers that are enabled by default on this target.
+    ///
+    /// Note that the support here is at a codegen level. If the machine code with sanitizer
+    /// enabled can generated on this target, but the necessary supporting libraries are not
+    /// distributed with the target, the sanitizer should still appear in this list for the target.
+    pub default_sanitizers: SanitizerSet,
+
     /// Minimum number of bits in #[repr(C)] enum. Defaults to the size of c_int
     pub c_enum_min_bits: Option<u64>,
 
@@ -2567,6 +2574,7 @@ impl Default for TargetOptions {
             // `Off` is supported by default, but targets can remove this manually, e.g. Windows.
             supported_split_debuginfo: Cow::Borrowed(&[SplitDebuginfo::Off]),
             supported_sanitizers: SanitizerSet::empty(),
+            default_sanitizers: SanitizerSet::empty(),
             c_enum_min_bits: None,
             generate_arange_section: true,
             supports_stack_protector: true,

compiler/rustc_target/src/spec/targets/aarch64_unknown_fuchsia.rs

@@ -12,6 +12,7 @@ pub(crate) fn target() -> Target {
         | SanitizerSet::CFI
         | SanitizerSet::LEAK
         | SanitizerSet::SHADOWCALLSTACK;
+    base.default_sanitizers = SanitizerSet::SHADOWCALLSTACK;
     base.supports_xray = true;
 
     base.add_pre_link_args(

compiler/rustc_target/src/spec/targets/riscv64gc_unknown_fuchsia.rs

@@ -9,6 +9,7 @@ pub(crate) fn target() -> Target {
     base.max_atomic_width = Some(64);
     base.stack_probes = StackProbeType::Inline;
     base.supported_sanitizers = SanitizerSet::SHADOWCALLSTACK;
+    base.default_sanitizers = SanitizerSet::SHADOWCALLSTACK;
     base.supports_xray = true;
 
     Target {