Rollup merge of rust-lang#157788 - PiJoules:multiple-sanitizer-flags, r=petrochenkov

Accumulate multiple -Zsanitizer target modifiers

When passing multiple `-Zsanitizer` flags to the compiler (e.g., `-Zsanitizer=address -Zsanitizer=shadow-call-stack`), the options parser was overwriting the previous values in `target_modifiers` instead of accumulating them. This resulted in only the last sanitizer being recorded in the crate metadata's target modifiers, even though the frontend correctly enabled all of them. The only way to provide multiple sanitizers is to combine them into a comma-separated list passed to a single `-Zsanitizer=` flag, but this doesn't fit very well into the GN build system where different targets may pass different combinations of sanitizer flags.

Consequently, this caused spurious "incompatible target modifiers" ABI mismatch errors when linking against dependencies compiled with accumulated flags.

Fix this by entry-modifying the `target_modifiers` map to accumulate the sanitizers as a comma-separated list when the option is `sanitizer`.

Author: JonathanBrouwer

compiler/rustc_session/src/options.rs

@@ -727,7 +727,25 @@ fn build_options<O: Default>(
                 }
                 if let Some(tmod) = *tmod {
                     let v = value.map_or(String::new(), ToOwned::to_owned);
-                    collected_options.target_modifiers.insert(tmod, v);
+
+                    // Accumulate all the -Zsanitizer flags into a single target modifier.
+                    match tmod {
+                        OptionsTargetModifiers::UnstableOptions(
+                            UnstableOptionsTargetModifiers::Sanitizer,
+                        ) => {
+                            collected_options
+                                .target_modifiers
+                                .entry(tmod)
+                                .and_modify(|existing| {
+                                    existing.push(',');
+                                    existing.push_str(&v);
+                                })
+                                .or_insert(v);
+                        }
+                        _ => {
+                            collected_options.target_modifiers.insert(tmod, v);
+                        }
+                    }
                 }
                 if let Some(mitigation) = mitigation {
                     collected_options.mitigations.reset_mitigation(*mitigation, index);

tests/codegen-llvm/sanitizer/multiple-sanitizers.rs

@@ -0,0 +1,16 @@
+// Verifies that multiple compatible sanitizers (CFI + SafeStack) can be enabled together
+// and their target modifiers accumulate instead of overwriting.
+//
+//@ only-x86_64
+//@ only-linux
+//@ compile-flags: -Zsanitizer=cfi -Zsanitizer=safestack -Clto -Ccodegen-units=1 -C unsafe-allow-abi-mismatch=sanitizer
+
+#![crate_type = "lib"]
+
+// CHECK: ; Function Attrs:{{.*}}safestack
+// CHECK: define{{.*}}foo{{.*}}!type
+pub fn foo(f: fn(i32) -> i32, arg: i32) -> i32 {
+    f(arg)
+}
+
+// CHECK: attributes #0 = {{.*}}safestack{{.*}}

tests/ui/target_modifiers/sanitizers-safestack-and-kcfi.missed_both.stderr

@@ -1,5 +1,5 @@
 error: mixing `-Zsanitizer` will cause an ABI mismatch in crate `sanitizers_safestack_and_kcfi`
-  --> $DIR/sanitizers-safestack-and-kcfi.rs:16:1
+  --> $DIR/sanitizers-safestack-and-kcfi.rs:18:1
    |
 LL | #![feature(no_core)]
    | ^

tests/ui/target_modifiers/sanitizers-safestack-and-kcfi.missed_kcfi.stderr

@@ -1,5 +1,5 @@
 error: mixing `-Zsanitizer` will cause an ABI mismatch in crate `sanitizers_safestack_and_kcfi`
-  --> $DIR/sanitizers-safestack-and-kcfi.rs:16:1
+  --> $DIR/sanitizers-safestack-and-kcfi.rs:18:1
    |
 LL | #![feature(no_core)]
    | ^

tests/ui/target_modifiers/sanitizers-safestack-and-kcfi.missed_safestack.stderr

@@ -1,5 +1,5 @@
 error: mixing `-Zsanitizer` will cause an ABI mismatch in crate `sanitizers_safestack_and_kcfi`
-  --> $DIR/sanitizers-safestack-and-kcfi.rs:16:1
+  --> $DIR/sanitizers-safestack-and-kcfi.rs:18:1
    |
 LL | #![feature(no_core)]
    | ^

tests/ui/target_modifiers/sanitizers-safestack-and-kcfi.rs

@@ -4,14 +4,16 @@
 //@ aux-build:safestack-and-kcfi.rs
 //@ compile-flags: -Cpanic=abort
 
-//@ revisions: good good_reverted missed_safestack missed_kcfi missed_both
+//@ revisions: good good_reverted good_multiple missed_safestack missed_kcfi missed_both
 //@[good] compile-flags: -Zsanitizer=safestack,kcfi
 //@[good_reverted] compile-flags: -Zsanitizer=kcfi,safestack
+//@[good_multiple] compile-flags: -Zsanitizer=safestack -Zsanitizer=kcfi
 //@[missed_safestack] compile-flags: -Zsanitizer=kcfi
 //@[missed_kcfi] compile-flags: -Zsanitizer=safestack
 // [missed_both] no additional compile-flags:
 //@[good] check-pass
 //@[good_reverted] check-pass
+//@[good_multiple] check-pass
 
 #![feature(no_core)]
 //[missed_safestack]~^ ERROR mixing `-Zsanitizer` will cause an ABI mismatch in crate `sanitizers_safestack_and_kcfi`