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These linkages were introduced some time ago, but it was never very clear what exactly their semantics were or what they should be used for. Some investigation found these uses: * utf-16 strings in clang. * non-unnamed_addr strings produced by the sanitizers. It turns out they were just working around a more fundamental problem. For some sections a MachO linker needs a symbol in order to split the section into atoms, and llvm had no idea that was the case. I fixed that in r201700 and it is now safe to use the private linkage. When the object ends up in a section that requires symbols, llvm will use a 'l' prefix instead of a 'L' prefix and things just work. With that, these linkages were already dead, but there was a potential future user in the objc metadata information. I am still looking at CGObjcMac.cpp, but at this point I am convinced that linker_private and linker_private_weak are not what they need. The objc uses are currently split in * Regular symbols (no '\01' prefix). LLVM already directly provides whatever semantics they need. * Uses of a private name (start with "\01L" or "\01l") and private linkage. We can drop the "\01L" and "\01l" prefixes as soon as llvm agrees with clang on L being ok or not for a given section. I have two patches in code review for this. * Uses of private name and weak linkage. The last case is the one that one could think would fit one of these linkages. That is not the case. The semantics are * the linker will merge these symbol by *name*. * the linker will hide them in the final DSO. Given that the merging is done by name, any of the private (or internal) linkages would be a bad match. They allow llvm to rename the symbols, and that is really not what we want. From the llvm point of view, these objects should really be (linkonce|weak)(_odr)?. For now, just keeping the "\01l" prefix is probably the best for these symbols. If we one day want to have a more direct support in llvm, IMHO what we should add is not a linkage, it is just a hidden_symbol attribute. It would be applicable to multiple linkages. For example, on weak it would produce the current behavior we have for objc metadata. On internal, it would be equivalent to private (and we should then remove private). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203866 91177308-0d34-0410-b5e6-96231b3b80d8
145 lines
4.7 KiB
C++
145 lines
4.7 KiB
C++
//===-- Mangler.cpp - Self-contained c/asm llvm name mangler --------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Unified name mangler for assembly backends.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/IR/Mangler.h"
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#include "llvm/ADT/SmallString.h"
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#include "llvm/ADT/Twine.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Function.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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static void getNameWithPrefixx(raw_ostream &OS, const Twine &GVName,
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Mangler::ManglerPrefixTy PrefixTy,
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const DataLayout &DL, bool UseAt) {
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SmallString<256> TmpData;
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StringRef Name = GVName.toStringRef(TmpData);
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assert(!Name.empty() && "getNameWithPrefix requires non-empty name");
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if (PrefixTy == Mangler::Private)
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OS << DL.getPrivateGlobalPrefix();
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else if (PrefixTy == Mangler::LinkerPrivate)
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OS << DL.getLinkerPrivateGlobalPrefix();
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if (UseAt) {
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OS << '@';
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} else {
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char Prefix = DL.getGlobalPrefix();
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if (Prefix != '\0')
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OS << Prefix;
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}
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// If this is a simple string that doesn't need escaping, just append it.
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OS << Name;
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}
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void Mangler::getNameWithPrefix(raw_ostream &OS, const Twine &GVName,
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ManglerPrefixTy PrefixTy) const {
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return getNameWithPrefixx(OS, GVName, PrefixTy, *DL, false);
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}
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void Mangler::getNameWithPrefix(SmallVectorImpl<char> &OutName,
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const Twine &GVName,
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ManglerPrefixTy PrefixTy) const {
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raw_svector_ostream OS(OutName);
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return getNameWithPrefix(OS, GVName, PrefixTy);
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}
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/// AddFastCallStdCallSuffix - Microsoft fastcall and stdcall functions require
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/// a suffix on their name indicating the number of words of arguments they
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/// take.
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static void AddFastCallStdCallSuffix(raw_ostream &OS, const Function *F,
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const DataLayout &TD) {
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// Calculate arguments size total.
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unsigned ArgWords = 0;
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for (Function::const_arg_iterator AI = F->arg_begin(), AE = F->arg_end();
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AI != AE; ++AI) {
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Type *Ty = AI->getType();
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// 'Dereference' type in case of byval or inalloca parameter attribute.
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if (AI->hasByValOrInAllocaAttr())
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Ty = cast<PointerType>(Ty)->getElementType();
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// Size should be aligned to DWORD boundary
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ArgWords += ((TD.getTypeAllocSize(Ty) + 3)/4)*4;
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}
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OS << '@' << ArgWords;
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}
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void Mangler::getNameWithPrefix(raw_ostream &OS, const GlobalValue *GV,
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bool CannotUsePrivateLabel) const {
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ManglerPrefixTy PrefixTy = Mangler::Default;
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if (GV->hasPrivateLinkage()) {
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if (CannotUsePrivateLabel)
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PrefixTy = Mangler::LinkerPrivate;
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else
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PrefixTy = Mangler::Private;
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}
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if (!GV->hasName()) {
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// Get the ID for the global, assigning a new one if we haven't got one
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// already.
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unsigned &ID = AnonGlobalIDs[GV];
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if (ID == 0)
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ID = NextAnonGlobalID++;
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// Must mangle the global into a unique ID.
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getNameWithPrefix(OS, "__unnamed_" + Twine(ID), PrefixTy);
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return;
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}
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StringRef Name = GV->getName();
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// No need to do anything special if the global has the special "do not
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// mangle" flag in the name.
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if (Name[0] == '\1') {
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OS << Name.substr(1);
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return;
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}
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bool UseAt = false;
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const Function *MSFunc = NULL;
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CallingConv::ID CC;
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if (DL->hasMicrosoftFastStdCallMangling()) {
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if ((MSFunc = dyn_cast<Function>(GV))) {
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CC = MSFunc->getCallingConv();
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// fastcall functions need to start with @ instead of _.
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if (CC == CallingConv::X86_FastCall)
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UseAt = true;
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}
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}
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getNameWithPrefixx(OS, Name, PrefixTy, *DL, UseAt);
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if (!MSFunc)
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return;
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// If we are supposed to add a microsoft-style suffix for stdcall/fastcall,
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// add it.
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// fastcall and stdcall functions usually need @42 at the end to specify
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// the argument info.
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FunctionType *FT = MSFunc->getFunctionType();
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if ((CC == CallingConv::X86_FastCall || CC == CallingConv::X86_StdCall) &&
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// "Pure" variadic functions do not receive @0 suffix.
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(!FT->isVarArg() || FT->getNumParams() == 0 ||
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(FT->getNumParams() == 1 && MSFunc->hasStructRetAttr())))
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AddFastCallStdCallSuffix(OS, MSFunc, *DL);
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}
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void Mangler::getNameWithPrefix(SmallVectorImpl<char> &OutName,
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const GlobalValue *GV,
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bool CannotUsePrivateLabel) const {
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raw_svector_ostream OS(OutName);
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getNameWithPrefix(OS, GV, CannotUsePrivateLabel);
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}
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