[Clang][CodeGen][ObjC]: Fix CoreFoundation on ELF with `-fconstant-cfstrings`.

[Clang][CodeGen][ObjC]: Fix non-bridged CoreFoundation builds on ELF targets
that use `-fconstant-cfstrings`. The original changes from differential
for a similar patch to PE/COFF (https://reviews.llvm.org/D44491) did not
check for an edge case where the global could be a constant which surfaced
as an issue when building for ELF because of different linkage semantics.

This patch addresses several issues with crashes related to CF builds on ELF
as well as improves data layout by ensuring string literals that back
the actual CFConstStrings end up in .rodata in line with Mach-O.

Change itself tested with CoreFoundation on Linux x86_64 but should be valid
for BSD-like systems as well that use ELF as the native object format.

Differential Revision: https://reviews.llvm.org/D52344

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@342883 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 85fed525795dd3dc2ec32bbf1b790a03ece0ee4a..baafa98d5c853501857b915b3b6851b1d9154fc6 100644 (file)
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -4109,37 +4109,48 @@ CodeGenModule::GetAddrOfConstantCFString(const StringLiteral *Literal) {
 
   llvm::Constant *Zero = llvm::Constant::getNullValue(Int32Ty);
   llvm::Constant *Zeros[] = { Zero, Zero };
-
+  
   // If we don't already have it, get __CFConstantStringClassReference.
   if (!CFConstantStringClassRef) {
     llvm::Type *Ty = getTypes().ConvertType(getContext().IntTy);
     Ty = llvm::ArrayType::get(Ty, 0);
-    llvm::GlobalValue *GV = cast<llvm::GlobalValue>(
-        CreateRuntimeVariable(Ty, "__CFConstantStringClassReference"));
-
-    if (getTriple().isOSBinFormatCOFF()) {
-      IdentifierInfo &II = getContext().Idents.get(GV->getName());
-      TranslationUnitDecl *TUDecl = getContext().getTranslationUnitDecl();
-      DeclContext *DC = TranslationUnitDecl::castToDeclContext(TUDecl);
-
-      const VarDecl *VD = nullptr;
-      for (const auto &Result : DC->lookup(&II))
-        if ((VD = dyn_cast<VarDecl>(Result)))
-          break;
-
-      if (!VD || !VD->hasAttr<DLLExportAttr>()) {
-        GV->setDLLStorageClass(llvm::GlobalValue::DLLImportStorageClass);
-        GV->setLinkage(llvm::GlobalValue::ExternalLinkage);
-      } else {
-        GV->setDLLStorageClass(llvm::GlobalValue::DLLExportStorageClass);
-        GV->setLinkage(llvm::GlobalValue::ExternalLinkage);
+    llvm::Constant *C =
+        CreateRuntimeVariable(Ty, "__CFConstantStringClassReference");
+    
+    if (getTriple().isOSBinFormatELF() || getTriple().isOSBinFormatCOFF()) {
+      llvm::GlobalValue *GV = nullptr;
+      
+      if ((GV = dyn_cast<llvm::GlobalValue>(C))) {
+        IdentifierInfo &II = getContext().Idents.get(GV->getName());
+        TranslationUnitDecl *TUDecl = getContext().getTranslationUnitDecl();
+        DeclContext *DC = TranslationUnitDecl::castToDeclContext(TUDecl);
+
+        const VarDecl *VD = nullptr;
+        for (const auto &Result : DC->lookup(&II))
+          if ((VD = dyn_cast<VarDecl>(Result)))
+            break;
+          
+        if (getTriple().isOSBinFormatELF()) {
+          if (!VD)
+            GV->setLinkage(llvm::GlobalValue::ExternalLinkage);
+        }
+        else {
+          if (!VD || !VD->hasAttr<DLLExportAttr>()) {
+            GV->setDLLStorageClass(llvm::GlobalValue::DLLImportStorageClass);
+            GV->setLinkage(llvm::GlobalValue::ExternalLinkage);
+          } else {
+            GV->setDLLStorageClass(llvm::GlobalValue::DLLExportStorageClass);
+            GV->setLinkage(llvm::GlobalValue::ExternalLinkage);
+          }
+        }
+        
+        setDSOLocal(GV);
       }
     }
-    setDSOLocal(GV);
-
+  
     // Decay array -> ptr
     CFConstantStringClassRef =
-        llvm::ConstantExpr::getGetElementPtr(Ty, GV, Zeros);
+        llvm::ConstantExpr::getGetElementPtr(Ty, C, Zeros);
   }
 
   QualType CFTy = getContext().getCFConstantStringType();
@@ -4185,7 +4196,11 @@ CodeGenModule::GetAddrOfConstantCFString(const StringLiteral *Literal) {
   if (getTriple().isOSBinFormatMachO())
     GV->setSection(isUTF16 ? "__TEXT,__ustring"
                            : "__TEXT,__cstring,cstring_literals");
-
+  // Make sure the literal ends up in .rodata to allow for safe ICF and for
+  // the static linker to adjust permissions to read-only later on.
+  else if (getTriple().isOSBinFormatELF())
+    GV->setSection(".rodata");
+  
   // String.
   llvm::Constant *Str =
       llvm::ConstantExpr::getGetElementPtr(GV->getValueType(), GV, Zeros);

diff --git a/test/CodeGen/cfstring-elf.c b/test/CodeGen/cfstring-elf.c
new file mode 100644 (file)
index 0000000..79fd9ba
--- /dev/null
+++ b/test/CodeGen/cfstring-elf.c
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 -triple x86_64-elf -DCF_BUILDING_CF -DDECL -S -emit-llvm %s -o - | FileCheck %s -check-prefix CHECK-CF-IN-CF-DECL
+// RUN: %clang_cc1 -triple x86_64-elf -DCF_BUILDING_CF -DDEFN -S -emit-llvm %s -o - | FileCheck %s -check-prefix CHECK-CF-IN-CF-DEFN
+// RUN: %clang_cc1 -triple x86_64-elf -S -emit-llvm %s -o - | FileCheck %s -check-prefix CHECK-CF
+// RUN: %clang_cc1 -triple x86_64-elf -DEXTERN -S -emit-llvm %s -o - | FileCheck %s -check-prefix CHECK-CF-EXTERN
+
+// RUN: %clang_cc1 -Os -triple x86_64-elf -DCF_BUILDING_CF -DDECL -S -emit-llvm %s -o - | FileCheck %s -check-prefix CHECK-CF-IN-CF-DECL
+// RUN: %clang_cc1 -Os -triple x86_64-elf -DCF_BUILDING_CF -DDEFN -S -emit-llvm %s -o - | FileCheck %s -check-prefix CHECK-CF-IN-CF-DEFN
+// RUN: %clang_cc1 -Os -triple x86_64-elf -S -emit-llvm %s -o - | FileCheck %s -check-prefix CHECK-CF
+// RUN: %clang_cc1 -Os -triple x86_64-elf -DEXTERN -S -emit-llvm %s -o - | FileCheck %s -check-prefix CHECK-CF-EXTERN
+
+
+#if defined(CF_BUILDING_CF)
+#if defined(DECL)
+extern long __CFConstantStringClassReference[];
+#elif defined(DEFN)
+long __CFConstantStringClassReference[32];
+#endif
+#else
+#if defined(EXTERN)
+extern long __CFConstantStringClassReference[];
+#else
+long __CFConstantStringClassReference[];
+#endif
+#endif
+
+typedef struct __CFString *CFStringRef;
+const CFStringRef string = (CFStringRef)__builtin___CFStringMakeConstantString("string");
+
+
+// CHECK-CF-IN-CF-DECL: @__CFConstantStringClassReference = external global [0 x i32]
+// CHECK-CF-IN-CF-DEFN: @__CFConstantStringClassReference = common global [32 x i64] zeroinitializer, align 16
+// CHECK-CF: @__CFConstantStringClassReference = common global [1 x i64] zeroinitializer, align 8
+// CHECK-CF-EXTERN: @__CFConstantStringClassReference = external global [0 x i32]
+// CHECK-CF-EXTERN: @.str = private unnamed_addr constant [7 x i8] c"string\00", section ".rodata", align 1