[lld][WebAssembly] Fix check for exporting mutable globals (llvm#160787)

We were not actually checking whether the global in question was
actually mutable before reporting the error.

Author: sbc100

lld/test/wasm/mutable-global-exports.s

@@ -16,6 +16,10 @@
 
 .globl _start
 .globl foo_global
+.globl bar_global
+
+.globaltype bar_global, i32, immutable
+bar_global:
 
 .globaltype foo_global, i32
 foo_global:
@@ -33,6 +37,7 @@ _start:
   .ascii  "atomics"
 
 # CHECK-ERR: mutable global exported but 'mutable-globals' feature not present in inputs: `foo_global`. Use --no-check-features to suppress
+# CHECK-ERR-NOT: bar_global
 
 #      CHECK:  - Type:            EXPORT
 # CHECK-NEXT:    Exports:
@@ -74,36 +79,39 @@ _start:
 # CHECK-ALL-NEXT:      - Name:            foo_global
 # CHECK-ALL-NEXT:        Kind:            GLOBAL
 # CHECK-ALL-NEXT:        Index:           1
-# CHECK-ALL-NEXT:      - Name:            __dso_handle
+# CHECK-ALL-NEXT:      - Name:            bar_global
 # CHECK-ALL-NEXT:        Kind:            GLOBAL
 # CHECK-ALL-NEXT:        Index:           2
-# CHECK-ALL-NEXT:      - Name:            __data_end
+# CHECK-ALL-NEXT:      - Name:            __dso_handle
 # CHECK-ALL-NEXT:        Kind:            GLOBAL
 # CHECK-ALL-NEXT:        Index:           3
-# CHECK-ALL-NEXT:      - Name:            __stack_low
+# CHECK-ALL-NEXT:      - Name:            __data_end
 # CHECK-ALL-NEXT:        Kind:            GLOBAL
 # CHECK-ALL-NEXT:        Index:           4
-# CHECK-ALL-NEXT:      - Name:            __stack_high
+# CHECK-ALL-NEXT:      - Name:            __stack_low
 # CHECK-ALL-NEXT:        Kind:            GLOBAL
 # CHECK-ALL-NEXT:        Index:           5
-# CHECK-ALL-NEXT:      - Name:            __global_base
+# CHECK-ALL-NEXT:      - Name:            __stack_high
 # CHECK-ALL-NEXT:        Kind:            GLOBAL
 # CHECK-ALL-NEXT:        Index:           6
-# CHECK-ALL-NEXT:      - Name:            __heap_base
+# CHECK-ALL-NEXT:      - Name:            __global_base
 # CHECK-ALL-NEXT:        Kind:            GLOBAL
 # CHECK-ALL-NEXT:        Index:           7
-# CHECK-ALL-NEXT:      - Name:            __heap_end
+# CHECK-ALL-NEXT:      - Name:            __heap_base
 # CHECK-ALL-NEXT:        Kind:            GLOBAL
 # CHECK-ALL-NEXT:        Index:           8
-# CHECK-ALL-NEXT:      - Name:            __memory_base
+# CHECK-ALL-NEXT:      - Name:            __heap_end
 # CHECK-ALL-NEXT:        Kind:            GLOBAL
 # CHECK-ALL-NEXT:        Index:           9
-# CHECK-ALL-NEXT:      - Name:            __table_base
+# CHECK-ALL-NEXT:      - Name:            __memory_base
 # CHECK-ALL-NEXT:        Kind:            GLOBAL
 # CHECK-ALL-NEXT:        Index:           10
-# CHECK-ALL-NEXT:      - Name:            __wasm_first_page_end
+# CHECK-ALL-NEXT:      - Name:            __table_base
 # CHECK-ALL-NEXT:        Kind:            GLOBAL
 # CHECK-ALL-NEXT:        Index:           11
+# CHECK-ALL-NEXT:      - Name:            __wasm_first_page_end
+# CHECK-ALL-NEXT:        Kind:            GLOBAL
+# CHECK-ALL-NEXT:        Index:           12
 # CHECK-ALL-NEXT:  - Type:            CODE
 
 # CHECK-ALL:         Name:            target_features

lld/wasm/Writer.cpp

@@ -576,7 +576,7 @@ void Writer::populateTargetFeatures() {
 
   if (ctx.isPic) {
     // This should not be necessary because all PIC objects should
-    // contain the mutable-globals feature.
+    // contain the `mutable-globals` feature.
     // TODO (https://github.com/llvm/llvm-project/issues/51681)
     allowed.insert("mutable-globals");
   }
@@ -703,10 +703,12 @@ void Writer::checkImportExportTargetFeatures() {
       }
     }
     for (const Symbol *sym : out.exportSec->exportedSymbols) {
-      if (isa<GlobalSymbol>(sym)) {
-        error(Twine("mutable global exported but 'mutable-globals' feature "
-                    "not present in inputs: `") +
-              toString(*sym) + "`. Use --no-check-features to suppress.");
+      if (auto *global = dyn_cast<GlobalSymbol>(sym)) {
+        if (global->getGlobalType()->Mutable) {
+          error(Twine("mutable global exported but 'mutable-globals' feature "
+                      "not present in inputs: `") +
+                toString(*sym) + "`. Use --no-check-features to suppress.");
+        }
       }
     }
   }