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The `-fwritable-strings' flag doesn't make the backing store strings of all 

CFStrings writable.

The strings (both Unicode and ASCII) should reside in a read-only section. E.g.,
__TEXT,__cstring instead of __DATA,__data. This is done by making the global
variable created for the strings constant despite the value of that flag.
<rdar://problem/10657500>

llvm-svn: 147845
This commit is contained in:
Bill Wendling 2012-01-10 08:46:39 +00:00
parent 430f3f1bd6
commit 86131f2c8d
2 changed files with 16 additions and 10 deletions
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16
clang/lib/CodeGen/CodeGenModule.cpp
View File

@ -1848,24 +1848,20 @@ CodeGenModule::GetAddrOfConstantCFString(const StringLiteral *Literal) {
llvm::Constant *C = llvm::ConstantArray::get(VMContext, Entry.getKey().str());
llvm::GlobalValue::LinkageTypes Linkage;
bool isConstant;
if (isUTF16) {
if (isUTF16)
// FIXME: why do utf strings get "_" labels instead of "L" labels?
Linkage = llvm::GlobalValue::InternalLinkage;
// Note: -fwritable-strings doesn't make unicode CFStrings writable, but
// does make plain ascii ones writable.
isConstant = true;
} else {
else
// FIXME: With OS X ld 123.2 (xcode 4) and LTO we would get a linker error
// when using private linkage. It is not clear if this is a bug in ld
// or a reasonable new restriction.
Linkage = llvm::GlobalValue::LinkerPrivateLinkage;
isConstant = !Features.WritableStrings;
}
// Note: -fwritable-strings doesn't make the backing store strings of
// CFStrings writable. (See <rdar://problem/10657500>)
llvm::GlobalVariable *GV =
new llvm::GlobalVariable(getModule(), C->getType(), isConstant, Linkage, C,
".str");
new llvm::GlobalVariable(getModule(), C->getType(), /*isConstant=*/true,
Linkage, C, ".str");
GV->setUnnamedAddr(true);
if (isUTF16) {
CharUnits Align = getContext().getTypeAlignInChars(getContext().ShortTy);

10
clang/test/CodeGen/cfstring.c
View File

@ -1,4 +1,14 @@
// RUN: %clang_cc1 -emit-llvm %s -o %t
// <rdar://problem/10657500>: Check that the backing store of CFStrings are
// constant with the -fwritable-strings flag.
//
// RUN: %clang_cc1 -fwritable-strings -emit-llvm %s -o - | FileCheck %s
//
// CHECK: @.str = linker_private unnamed_addr constant [14 x i8] c"Hello, World!\00", align 1
// CHECK: @.str1 = linker_private unnamed_addr constant [7 x i8] c"yo joe\00", align 1
// CHECK: @.str3 = linker_private unnamed_addr constant [16 x i8] c"Goodbye, World!\00", align 1
#define CFSTR __builtin___CFStringMakeConstantString
void f() {