Target modifiers (special marked options) are recorded in metainfo

compiler/rustc_interface/src/passes.rs

@@ -269,6 +269,7 @@ fn configure_and_expand(
 
     resolver.resolve_crate(&krate);
 
+    CStore::from_tcx(tcx).report_incompatible_target_modifiers(tcx, &krate);
     krate
 }
 

compiler/rustc_metadata/messages.ftl

@@ -113,6 +113,14 @@ metadata_incompatible_rustc =
     found crate `{$crate_name}` compiled by an incompatible version of rustc{$add_info}
     .help = please recompile that crate using this compiler ({$rustc_version}) (consider running `cargo clean` first)
 
+metadata_incompatible_target_modifiers =
+    mixing `{$flag_name_prefixed}` will cause an ABI mismatch in crate `{$local_crate}`
+    .note = `{$flag_name_prefixed}={$flag_local_value}` in this crate is incompatible with `{$flag_name_prefixed}={$flag_extern_value}` in dependency `{$extern_crate}`
+    .help = the `{$flag_name_prefixed}` flag modifies the ABI so Rust crates compiled with different values of this flag cannot be used together safely
+
+metadata_incompatible_target_modifiers_help_allow = if you are sure this will not cause problems, you may use `-Cunsafe-allow-abi-mismatch={$flag_name}` to silence this error
+metadata_incompatible_target_modifiers_help_fix = set `{$flag_name_prefixed}={$flag_extern_value}` in this crate or `{$flag_name_prefixed}={$flag_local_value}` in `{$extern_crate}`
+
 metadata_incompatible_wasm_link =
     `wasm_import_module` is incompatible with other arguments in `#[link]` attributes
 
@@ -284,6 +292,8 @@ metadata_unknown_link_kind =
 metadata_unknown_link_modifier =
     unknown linking modifier `{$modifier}`, expected one of: bundle, verbatim, whole-archive, as-needed
 
+metadata_unknown_target_modifier_unsafe_allowed = unknown target modifier `{$flag_name}`, requested by `-Cunsafe-allow-abi-mismatch={$flag_name}`
+
 metadata_unsupported_abi =
     ABI not supported by `#[link(kind = "raw-dylib")]` on this architecture
 

compiler/rustc_metadata/src/creader.rs

@@ -23,7 +23,10 @@ use rustc_hir::definitions::Definitions;
 use rustc_index::IndexVec;
 use rustc_middle::bug;
 use rustc_middle::ty::{TyCtxt, TyCtxtFeed};
-use rustc_session::config::{self, CrateType, ExternLocation};
+use rustc_session::config::{
+    self, CrateType, ExtendedTargetModifierInfo, ExternLocation, OptionsTargetModifiers,
+    TargetModifier,
+};
 use rustc_session::cstore::{CrateDepKind, CrateSource, ExternCrate, ExternCrateSource};
 use rustc_session::lint::{self, BuiltinLintDiag};
 use rustc_session::output::validate_crate_name;
@@ -35,7 +38,9 @@ use tracing::{debug, info, trace};
 
 use crate::errors;
 use crate::locator::{CrateError, CrateLocator, CratePaths};
-use crate::rmeta::{CrateDep, CrateMetadata, CrateNumMap, CrateRoot, MetadataBlob};
+use crate::rmeta::{
+    CrateDep, CrateMetadata, CrateNumMap, CrateRoot, MetadataBlob, TargetModifiers,
+};
 
 /// The backend's way to give the crate store access to the metadata in a library.
 /// Note that it returns the raw metadata bytes stored in the library file, whether
@@ -296,6 +301,94 @@ impl CStore {
         }
     }
 
+    fn report_target_modifiers_extended(
+        tcx: TyCtxt<'_>,
+        krate: &Crate,
+        mods: &TargetModifiers,
+        dep_mods: &TargetModifiers,
+        data: &CrateMetadata,
+    ) {
+        let span = krate.spans.inner_span.shrink_to_lo();
+        let allowed_flag_mismatches = &tcx.sess.opts.cg.unsafe_allow_abi_mismatch;
+        let name = tcx.crate_name(LOCAL_CRATE);
+        let tmod_extender = |tmod: &TargetModifier| (tmod.extend(), tmod.clone());
+        let report_diff = |prefix: &String,
+                           opt_name: &String,
+                           flag_local_value: &String,
+                           flag_extern_value: &String| {
+            if allowed_flag_mismatches.contains(&opt_name) {
+                return;
+            }
+            tcx.dcx().emit_err(errors::IncompatibleTargetModifiers {
+                span,
+                extern_crate: data.name(),
+                local_crate: name,
+                flag_name: opt_name.clone(),
+                flag_name_prefixed: format!("-{}{}", prefix, opt_name),
+                flag_local_value: flag_local_value.to_string(),
+                flag_extern_value: flag_extern_value.to_string(),
+            });
+        };
+        let mut it1 = mods.iter().map(tmod_extender);
+        let mut it2 = dep_mods.iter().map(tmod_extender);
+        let mut left_name_val: Option<(ExtendedTargetModifierInfo, TargetModifier)> = None;
+        let mut right_name_val: Option<(ExtendedTargetModifierInfo, TargetModifier)> = None;
+        let no_val = "*".to_string();
+        loop {
+            left_name_val = left_name_val.or_else(|| it1.next());
+            right_name_val = right_name_val.or_else(|| it2.next());
+            match (&left_name_val, &right_name_val) {
+                (Some(l), Some(r)) => match l.1.opt.cmp(&r.1.opt) {
+                    cmp::Ordering::Equal => {
+                        if l.0.tech_value != r.0.tech_value {
+                            report_diff(&l.0.prefix, &l.0.name, &l.1.value_name, &r.1.value_name);
+                        }
+                        left_name_val = None;
+                        right_name_val = None;
+                    }
+                    cmp::Ordering::Greater => {
+                        report_diff(&r.0.prefix, &r.0.name, &no_val, &r.1.value_name);
+                        right_name_val = None;
+                    }
+                    cmp::Ordering::Less => {
+                        report_diff(&l.0.prefix, &l.0.name, &l.1.value_name, &no_val);
+                        left_name_val = None;
+                    }
+                },
+                (Some(l), None) => {
+                    report_diff(&l.0.prefix, &l.0.name, &l.1.value_name, &no_val);
+                    left_name_val = None;
+                }
+                (None, Some(r)) => {
+                    report_diff(&r.0.prefix, &r.0.name, &no_val, &r.1.value_name);
+                    right_name_val = None;
+                }
+                (None, None) => break,
+            }
+        }
+    }
+
+    pub fn report_incompatible_target_modifiers(&self, tcx: TyCtxt<'_>, krate: &Crate) {
+        for flag_name in &tcx.sess.opts.cg.unsafe_allow_abi_mismatch {
+            if !OptionsTargetModifiers::is_target_modifier(flag_name) {
+                tcx.dcx().emit_err(errors::UnknownTargetModifierUnsafeAllowed {
+                    span: krate.spans.inner_span.shrink_to_lo(),
+                    flag_name: flag_name.clone(),
+                });
+            }
+        }
+        let mods = tcx.sess.opts.gather_target_modifiers();
+        for (_cnum, data) in self.iter_crate_data() {
+            if data.is_proc_macro_crate() {
+                continue;
+            }
+            let dep_mods = data.target_modifiers();
+            if mods != dep_mods {
+                Self::report_target_modifiers_extended(tcx, krate, &mods, &dep_mods, data);
+            }
+        }
+    }
+
     pub fn new(metadata_loader: Box<MetadataLoaderDyn>) -> CStore {
         CStore {
             metadata_loader,

compiler/rustc_metadata/src/errors.rs

@@ -739,3 +739,28 @@ pub(crate) struct WasmCAbi {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(metadata_incompatible_target_modifiers)]
+#[help]
+#[note]
+#[help(metadata_incompatible_target_modifiers_help_fix)]
+#[help(metadata_incompatible_target_modifiers_help_allow)]
+pub struct IncompatibleTargetModifiers {
+    #[primary_span]
+    pub span: Span,
+    pub extern_crate: Symbol,
+    pub local_crate: Symbol,
+    pub flag_name: String,
+    pub flag_name_prefixed: String,
+    pub flag_local_value: String,
+    pub flag_extern_value: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(metadata_unknown_target_modifier_unsafe_allowed)]
+pub struct UnknownTargetModifierUnsafeAllowed {
+    #[primary_span]
+    pub span: Span,
+    pub flag_name: String,
+}

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -29,6 +29,7 @@ use rustc_middle::{bug, implement_ty_decoder};
 use rustc_serialize::opaque::MemDecoder;
 use rustc_serialize::{Decodable, Decoder};
 use rustc_session::Session;
+use rustc_session::config::TargetModifier;
 use rustc_session::cstore::{CrateSource, ExternCrate};
 use rustc_span::hygiene::HygieneDecodeContext;
 use rustc_span::{BytePos, DUMMY_SP, Pos, SpanData, SpanDecoder, SyntaxContext, kw};
@@ -73,6 +74,9 @@ impl MetadataBlob {
 /// own crate numbers.
 pub(crate) type CrateNumMap = IndexVec<CrateNum, CrateNum>;
 
+/// Target modifiers - abi or exploit mitigations flags
+pub(crate) type TargetModifiers = Vec<TargetModifier>;
+
 pub(crate) struct CrateMetadata {
     /// The primary crate data - binary metadata blob.
     blob: MetadataBlob,
@@ -961,6 +965,13 @@ impl CrateRoot {
     ) -> impl ExactSizeIterator<Item = CrateDep> + Captures<'a> {
         self.crate_deps.decode(metadata)
     }
+
+    pub(crate) fn decode_target_modifiers<'a>(
+        &self,
+        metadata: &'a MetadataBlob,
+    ) -> impl ExactSizeIterator<Item = TargetModifier> + Captures<'a> {
+        self.target_modifiers.decode(metadata)
+    }
 }
 
 impl<'a> CrateMetadataRef<'a> {
@@ -1883,6 +1894,10 @@ impl CrateMetadata {
         self.dependencies.push(cnum);
     }
 
+    pub(crate) fn target_modifiers(&self) -> TargetModifiers {
+        self.root.decode_target_modifiers(&self.blob).collect()
+    }
+
     pub(crate) fn update_extern_crate(&mut self, new_extern_crate: ExternCrate) -> bool {
         let update =
             Some(new_extern_crate.rank()) > self.extern_crate.as_ref().map(ExternCrate::rank);

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -25,7 +25,7 @@ use rustc_middle::ty::{AssocItemContainer, SymbolName};
 use rustc_middle::util::common::to_readable_str;
 use rustc_middle::{bug, span_bug};
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder, opaque};
-use rustc_session::config::{CrateType, OptLevel};
+use rustc_session::config::{CrateType, OptLevel, TargetModifier};
 use rustc_span::hygiene::HygieneEncodeContext;
 use rustc_span::{
     ExternalSource, FileName, SourceFile, SpanData, SpanEncoder, StableSourceFileId, SyntaxContext,
@@ -692,6 +692,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         // Encode source_map. This needs to be done last, because encoding `Span`s tells us which
         // `SourceFiles` we actually need to encode.
         let source_map = stat!("source-map", || self.encode_source_map());
+        let target_modifiers = stat!("target-modifiers", || self.encode_target_modifiers());
 
         let root = stat!("final", || {
             let attrs = tcx.hir().krate_attrs();
@@ -735,6 +736,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 native_libraries,
                 foreign_modules,
                 source_map,
+                target_modifiers,
                 traits,
                 impls,
                 incoherent_impls,
@@ -2009,6 +2011,12 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         self.lazy_array(deps.iter().map(|(_, dep)| dep))
     }
 
+    fn encode_target_modifiers(&mut self) -> LazyArray<TargetModifier> {
+        empty_proc_macro!(self);
+        let tcx = self.tcx;
+        self.lazy_array(tcx.sess.opts.gather_target_modifiers())
+    }
+
     fn encode_lib_features(&mut self) -> LazyArray<(Symbol, FeatureStability)> {
         empty_proc_macro!(self);
         let tcx = self.tcx;

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -1,7 +1,7 @@
 use std::marker::PhantomData;
 use std::num::NonZero;
 
-pub(crate) use decoder::{CrateMetadata, CrateNumMap, MetadataBlob};
+pub(crate) use decoder::{CrateMetadata, CrateNumMap, MetadataBlob, TargetModifiers};
 use decoder::{DecodeContext, Metadata};
 use def_path_hash_map::DefPathHashMapRef;
 use encoder::EncodeContext;
@@ -32,7 +32,7 @@ use rustc_middle::ty::{
 use rustc_middle::util::Providers;
 use rustc_middle::{mir, trivially_parameterized_over_tcx};
 use rustc_serialize::opaque::FileEncoder;
-use rustc_session::config::SymbolManglingVersion;
+use rustc_session::config::{SymbolManglingVersion, TargetModifier};
 use rustc_session::cstore::{CrateDepKind, ForeignModule, LinkagePreference, NativeLib};
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::{ExpnIndex, MacroKind, SyntaxContextData};
@@ -282,6 +282,7 @@ pub(crate) struct CrateRoot {
     def_path_hash_map: LazyValue<DefPathHashMapRef<'static>>,
 
     source_map: LazyTable<u32, Option<LazyValue<rustc_span::SourceFile>>>,
+    target_modifiers: LazyArray<TargetModifier>,
 
     compiler_builtins: bool,
     needs_allocator: bool,

compiler/rustc_middle/src/ty/parameterized.rs

@@ -101,6 +101,7 @@ trivially_parameterized_over_tcx! {
     rustc_session::cstore::ForeignModule,
     rustc_session::cstore::LinkagePreference,
     rustc_session::cstore::NativeLib,
+    rustc_session::config::TargetModifier,
     rustc_span::ExpnData,
     rustc_span::ExpnHash,
     rustc_span::ExpnId,

compiler/rustc_session/src/config.rs

@@ -1191,6 +1191,7 @@ impl Default for Options {
             color: ColorConfig::Auto,
             logical_env: FxIndexMap::default(),
             verbose: false,
+            target_modifiers: BTreeMap::default(),
         }
     }
 }
@@ -2337,14 +2338,16 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
     let crate_types = parse_crate_types_from_list(unparsed_crate_types)
         .unwrap_or_else(|e| early_dcx.early_fatal(e));
 
-    let mut unstable_opts = UnstableOptions::build(early_dcx, matches);
+    let mut target_modifiers = BTreeMap::<OptionsTargetModifiers, String>::new();
+
+    let mut unstable_opts = UnstableOptions::build(early_dcx, matches, &mut target_modifiers);
     let (lint_opts, describe_lints, lint_cap) = get_cmd_lint_options(early_dcx, matches);
 
     check_error_format_stability(early_dcx, &unstable_opts, error_format);
 
     let output_types = parse_output_types(early_dcx, &unstable_opts, matches);
 
-    let mut cg = CodegenOptions::build(early_dcx, matches);
+    let mut cg = CodegenOptions::build(early_dcx, matches, &mut target_modifiers);
     let (disable_local_thinlto, codegen_units) = should_override_cgus_and_disable_thinlto(
         early_dcx,
         &output_types,
@@ -2615,6 +2618,7 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
         color,
         logical_env,
         verbose,
+        target_modifiers,
     }
 }
 

compiler/rustc_session/src/lib.rs

@@ -4,6 +4,9 @@
 #![feature(let_chains)]
 #![feature(map_many_mut)]
 #![feature(rustc_attrs)]
+// To generate CodegenOptionsTargetModifiers and UnstableOptionsTargetModifiers enums
+// with macro_rules, it is necessary to use recursive mechanic ("Incremental TT Munchers").
+#![recursion_limit = "256"]
 #![warn(unreachable_pub)]
 // tidy-alphabetical-end
 

src/librustdoc/config.rs

@@ -9,8 +9,8 @@ use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::DiagCtxtHandle;
 use rustc_session::config::{
     self, CodegenOptions, CrateType, ErrorOutputType, Externs, Input, JsonUnusedExterns,
-    UnstableOptions, get_cmd_lint_options, nightly_options, parse_crate_types_from_list,
-    parse_externs, parse_target_triple,
+    OptionsTargetModifiers, UnstableOptions, get_cmd_lint_options, nightly_options,
+    parse_crate_types_from_list, parse_externs, parse_target_triple,
 };
 use rustc_session::lint::Level;
 use rustc_session::search_paths::SearchPath;
@@ -387,8 +387,9 @@ impl Options {
             config::parse_error_format(early_dcx, matches, color, json_color, json_rendered);
         let diagnostic_width = matches.opt_get("diagnostic-width").unwrap_or_default();
 
-        let codegen_options = CodegenOptions::build(early_dcx, matches);
-        let unstable_opts = UnstableOptions::build(early_dcx, matches);
+        let mut target_modifiers = BTreeMap::<OptionsTargetModifiers, String>::new();
+        let codegen_options = CodegenOptions::build(early_dcx, matches, &mut target_modifiers);
+        let unstable_opts = UnstableOptions::build(early_dcx, matches, &mut target_modifiers);
 
         let remap_path_prefix = match parse_remap_path_prefix(matches) {
             Ok(prefix_mappings) => prefix_mappings,

tests/ui/target_modifiers/auxiliary/default_reg_struct_return.rs

@@ -0,0 +1,20 @@
+//@ compile-flags: --target i686-unknown-linux-gnu -Cpanic=abort
+// Auxiliary build problems with aarch64-apple:
+// Shared library linking cc seems to convert "-m32" flag into -arch armv4t
+// Auxiliary build problems with i686-mingw: linker `cc` not found
+//@ only-x86
+//@ ignore-windows
+//@ ignore-apple
+//@ needs-llvm-components: x86
+#![crate_type = "rlib"]
+#![no_core]
+#![feature(no_core, lang_items, repr_simd)]
+
+#[lang = "sized"]
+trait Sized {}
+#[lang = "copy"]
+trait Copy {}
+
+pub fn somefun() {}
+
+pub struct S;

tests/ui/target_modifiers/auxiliary/wrong_regparm.rs

@@ -0,0 +1,20 @@
+//@ compile-flags: --target i686-unknown-linux-gnu -Zregparm=2 -Cpanic=abort
+// Auxiliary build problems with aarch64-apple:
+// Shared library linking cc seems to convert "-m32" flag into -arch armv4t
+// Auxiliary build problems with i686-mingw: linker `cc` not found
+//@ only-x86
+//@ ignore-windows
+//@ ignore-apple
+//@ needs-llvm-components: x86
+#![crate_type = "rlib"]
+#![no_core]
+#![feature(no_core, lang_items, repr_simd)]
+
+#[lang = "sized"]
+trait Sized {}
+#[lang = "copy"]
+trait Copy {}
+
+pub fn somefun() {}
+
+pub struct S;

tests/ui/target_modifiers/auxiliary/wrong_regparm_and_ret.rs

@@ -0,0 +1,20 @@
+//@ compile-flags: --target i686-unknown-linux-gnu -Zregparm=2 -Zreg-struct-return=true -Cpanic=abort
+// Auxiliary build problems with aarch64-apple:
+// Shared library linking cc seems to convert "-m32" flag into -arch armv4t
+// Auxiliary build problems with i686-mingw: linker `cc` not found
+//@ only-x86
+//@ ignore-windows
+//@ ignore-apple
+//@ needs-llvm-components: x86
+#![crate_type = "rlib"]
+#![no_core]
+#![feature(no_core, lang_items, repr_simd)]
+
+#[lang = "sized"]
+trait Sized {}
+#[lang = "copy"]
+trait Copy {}
+
+pub fn somefun() {}
+
+pub struct S;

tests/ui/target_modifiers/defaults_check.error.stderr

@@ -0,0 +1,13 @@
+error: mixing `-Zreg-struct-return` will cause an ABI mismatch in crate `defaults_check`
+  --> $DIR/defaults_check.rs:20:1
+   |
+LL | #![crate_type = "rlib"]
+   | ^
+   |
+   = help: the `-Zreg-struct-return` flag modifies the ABI so Rust crates compiled with different values of this flag cannot be used together safely
+   = note: `-Zreg-struct-return=true` in this crate is incompatible with `-Zreg-struct-return=` in dependency `default_reg_struct_return`
+   = help: set `-Zreg-struct-return=` in this crate or `-Zreg-struct-return=true` in `default_reg_struct_return`
+   = help: if you are sure this will not cause problems, you may use `-Cunsafe-allow-abi-mismatch=reg-struct-return` to silence this error
+
+error: aborting due to 1 previous error
+

tests/ui/target_modifiers/defaults_check.rs

@@ -0,0 +1,27 @@
+// Tests that default unspecified target modifier value in dependency crate is ok linked
+// with the same value, explicitly specified
+//@ aux-crate:default_reg_struct_return=default_reg_struct_return.rs
+//@ compile-flags: --target i686-unknown-linux-gnu -Cpanic=abort
+//@ revisions:error ok ok_explicit
+//@[ok] compile-flags:
+//@[ok_explicit] compile-flags: -Zreg-struct-return=false
+//@[error] compile-flags: -Zreg-struct-return=true
+
+// Auxiliary build problems with aarch64-apple:
+// Shared library linking cc seems to convert "-m32" flag into -arch armv4t
+// Auxiliary build problems with i686-mingw: linker `cc` not found
+//@ only-x86
+//@ ignore-windows
+//@ ignore-apple
+//@ needs-llvm-components: x86
+//@[ok] build-pass
+//@[ok_explicit] build-pass
+
+#![crate_type = "rlib"]
+//[error]~^ ERROR mixing `-Zreg-struct-return` will cause an ABI mismatch in crate `defaults_check`
+#![no_core]
+#![feature(no_core, lang_items, repr_simd)]
+
+fn foo() {
+    default_reg_struct_return::somefun();
+}

tests/ui/target_modifiers/incompatible_regparm.allow_no_value.stderr

@@ -0,0 +1,2 @@
+error: codegen option `unsafe-allow-abi-mismatch` requires a comma-separated list of strings (C unsafe-allow-abi-mismatch=<value>)
+

tests/ui/target_modifiers/incompatible_regparm.error_generated.stderr

@@ -0,0 +1,13 @@
+error: mixing `-Zregparm` will cause an ABI mismatch in crate `incompatible_regparm`
+  --> $DIR/incompatible_regparm.rs:16:1
+   |
+LL | #![crate_type = "rlib"]
+   | ^
+   |
+   = help: the `-Zregparm` flag modifies the ABI so Rust crates compiled with different values of this flag cannot be used together safely
+   = note: `-Zregparm=1` in this crate is incompatible with `-Zregparm=2` in dependency `wrong_regparm`
+   = help: set `-Zregparm=2` in this crate or `-Zregparm=1` in `wrong_regparm`
+   = help: if you are sure this will not cause problems, you may use `-Cunsafe-allow-abi-mismatch=regparm` to silence this error
+
+error: aborting due to 1 previous error
+

tests/ui/target_modifiers/incompatible_regparm.rs

@@ -0,0 +1,23 @@
+//@ aux-crate:wrong_regparm=wrong_regparm.rs
+//@ compile-flags: --target i686-unknown-linux-gnu -Zregparm=1 -Cpanic=abort
+// Auxiliary build problems with aarch64-apple:
+// Shared library linking cc seems to convert "-m32" flag into -arch armv4t
+// Auxiliary build problems with i686-mingw: linker `cc` not found
+//@ only-x86
+//@ ignore-windows
+//@ ignore-apple
+//@ needs-llvm-components: x86
+//@ revisions:error_generated allow_regparm_mismatch allow_no_value
+
+//@[allow_regparm_mismatch] compile-flags: -Cunsafe-allow-abi-mismatch=regparm
+//@[allow_regparm_mismatch] build-pass
+//@[allow_no_value] compile-flags: -Cunsafe-allow-abi-mismatch
+
+#![crate_type = "rlib"]
+//[error_generated]~^ ERROR mixing `-Zregparm` will cause an ABI mismatch in crate `incompatible_regparm`
+#![no_core]
+#![feature(no_core, lang_items, repr_simd)]
+
+fn foo() {
+    wrong_regparm::somefun();
+}

tests/ui/target_modifiers/two_flags.rs

@@ -0,0 +1,23 @@
+//@ aux-crate:wrong_regparm_and_ret=wrong_regparm_and_ret.rs
+//@ compile-flags: --target i686-unknown-linux-gnu -Cpanic=abort
+// Auxiliary build problems with aarch64-apple:
+// Shared library linking cc seems to convert "-m32" flag into -arch armv4t
+// Auxiliary build problems with i686-mingw: linker `cc` not found
+//@ only-x86
+//@ ignore-windows
+//@ ignore-apple
+//@ needs-llvm-components: x86
+//@ revisions:two_allowed unknown_allowed
+
+//@[two_allowed] compile-flags: -Cunsafe-allow-abi-mismatch=regparm,reg-struct-return
+//@[two_allowed] build-pass
+//@[unknown_allowed] compile-flags: -Cunsafe-allow-abi-mismatch=unknown_flag -Zregparm=2 -Zreg-struct-return=true
+
+#![crate_type = "rlib"]
+//[unknown_allowed]~^ ERROR unknown target modifier `unknown_flag`, requested by `-Cunsafe-allow-abi-mismatch=unknown_flag`
+#![no_core]
+#![feature(no_core, lang_items, repr_simd)]
+
+fn foo() {
+    wrong_regparm_and_ret::somefun();
+}

tests/ui/target_modifiers/two_flags.unknown_allowed.stderr

@@ -0,0 +1,8 @@
+error: unknown target modifier `unknown_flag`, requested by `-Cunsafe-allow-abi-mismatch=unknown_flag`
+  --> $DIR/two_flags.rs:16:1
+   |
+LL | #![crate_type = "rlib"]
+   | ^
+
+error: aborting due to 1 previous error
+