LTOModule.cpp   [plain text]

//===-- LTOModule.cpp - LLVM Link Time Optimizer --------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
// This file implements the Link Time Optimization library. This library is 
// intended to be used by linker to optimize code at link time.
//
//===----------------------------------------------------------------------===//

#include "LTOModule.h"

#include "llvm/Constants.h"
#include "llvm/LLVMContext.h"
#include "llvm/Module.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/ADT/Triple.h"
#include "llvm/Bitcode/ReaderWriter.h"
#include "llvm/Support/SystemUtils.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/System/Host.h"
#include "llvm/System/Path.h"
#include "llvm/System/Process.h"
#include "llvm/Target/Mangler.h"
#include "llvm/Target/SubtargetFeature.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegistry.h"
#include "llvm/Target/TargetSelect.h"

using namespace llvm;

bool LTOModule::isBitcodeFile(const void* mem, size_t length)
{
    return llvm::sys::IdentifyFileType((char*)mem, length) 
        == llvm::sys::Bitcode_FileType;
}

bool LTOModule::isBitcodeFile(const char* path)
{
    return llvm::sys::Path(path).isBitcodeFile();
}

bool LTOModule::isBitcodeFileForTarget(const void* mem, size_t length,
                                       const char* triplePrefix) 
{
    MemoryBuffer* buffer = makeBuffer(mem, length);
    if (!buffer)
        return false;
    return isTargetMatch(buffer, triplePrefix);
}


bool LTOModule::isBitcodeFileForTarget(const char* path,
                                       const char* triplePrefix) 
{
    MemoryBuffer *buffer = MemoryBuffer::getFile(path);
    if (buffer == NULL)
        return false;
    return isTargetMatch(buffer, triplePrefix);
}

// takes ownership of buffer
bool LTOModule::isTargetMatch(MemoryBuffer* buffer, const char* triplePrefix)
{
    OwningPtr<Module> m(getLazyBitcodeModule(buffer, getGlobalContext()));
    // on success, m owns buffer and both are deleted at end of this method
    if (!m) {
        delete buffer;
        return false;
    }
    std::string actualTarget = m->getTargetTriple();
    return (strncmp(actualTarget.c_str(), triplePrefix, 
                    strlen(triplePrefix)) == 0);
}


LTOModule::LTOModule(Module* m, TargetMachine* t) 
 : _module(m), _target(t), _symbolsParsed(false)
{
}

LTOModule* LTOModule::makeLTOModule(const char* path,
                                    std::string& errMsg)
{
    OwningPtr<MemoryBuffer> buffer(MemoryBuffer::getFile(path, &errMsg));
    if (!buffer)
        return NULL;
    return makeLTOModule(buffer.get(), errMsg);
}

/// makeBuffer - create a MemoryBuffer from a memory range.
/// MemoryBuffer requires the byte past end of the buffer to be a zero.
/// We might get lucky and already be that way, otherwise make a copy.
/// Also if next byte is on a different page, don't assume it is readable.
MemoryBuffer* LTOModule::makeBuffer(const void* mem, size_t length)
{
    const char *startPtr = (char*)mem;
    const char *endPtr = startPtr+length;
    if (((uintptr_t)endPtr & (sys::Process::GetPageSize()-1)) == 0 ||
        *endPtr != 0) 
        return MemoryBuffer::getMemBufferCopy(StringRef(startPtr, length));
  
    return MemoryBuffer::getMemBuffer(StringRef(startPtr, length));
}


LTOModule* LTOModule::makeLTOModule(const void* mem, size_t length, 
                                    std::string& errMsg)
{
    OwningPtr<MemoryBuffer> buffer(makeBuffer(mem, length));
    if (!buffer)
        return NULL;
    return makeLTOModule(buffer.get(), errMsg);
}

LTOModule* LTOModule::makeLTOModule(MemoryBuffer* buffer,
                                    std::string& errMsg)
{
    InitializeAllTargets();

    // parse bitcode buffer
    OwningPtr<Module> m(ParseBitcodeFile(buffer, getGlobalContext(), &errMsg));
    if (!m)
        return NULL;

    std::string Triple = m->getTargetTriple();
    if (Triple.empty())
      Triple = sys::getHostTriple();

    // find machine architecture for this module
    const Target* march = TargetRegistry::lookupTarget(Triple, errMsg);
    if (!march) 
        return NULL;

    // construct LTModule, hand over ownership of module and target
    SubtargetFeatures Features;
    Features.getDefaultSubtargetFeatures("" /* cpu */, llvm::Triple(Triple));
    std::string FeatureStr = Features.getString();
    TargetMachine* target = march->createTargetMachine(Triple, FeatureStr);
    return new LTOModule(m.take(), target);
}


const char* LTOModule::getTargetTriple()
{
    return _module->getTargetTriple().c_str();
}

void LTOModule::addDefinedFunctionSymbol(Function* f, Mangler &mangler)
{
    // add to list of defined symbols
    addDefinedSymbol(f, mangler, true); 

    // add external symbols referenced by this function.
    for (Function::iterator b = f->begin(); b != f->end(); ++b) {
        for (BasicBlock::iterator i = b->begin(); i != b->end(); ++i) {
            for (unsigned count = 0, total = i->getNumOperands(); 
                                        count != total; ++count) {
                findExternalRefs(i->getOperand(count), mangler);
            }
        }
    }
}

// get string that data pointer points to 
bool LTOModule::objcClassNameFromExpression(Constant* c, std::string& name)
{
    if (ConstantExpr* ce = dyn_cast<ConstantExpr>(c)) {
        Constant* op = ce->getOperand(0);
        if (GlobalVariable* gvn = dyn_cast<GlobalVariable>(op)) {
            Constant* cn = gvn->getInitializer(); 
            if (ConstantArray* ca = dyn_cast<ConstantArray>(cn)) {
                if (ca->isCString()) {
                    name = ".objc_class_name_" + ca->getAsString();
                    return true;
                }
            }
        }
    }
    return false;
}

// parse i386/ppc ObjC class data structure 
void LTOModule::addObjCClass(GlobalVariable* clgv)
{
    if (ConstantStruct* c = dyn_cast<ConstantStruct>(clgv->getInitializer())) {
        // second slot in __OBJC,__class is pointer to superclass name
        std::string superclassName;
        if (objcClassNameFromExpression(c->getOperand(1), superclassName)) {
            NameAndAttributes info;
            if (_undefines.find(superclassName.c_str()) == _undefines.end()) {
                const char* symbolName = ::strdup(superclassName.c_str());
                info.name = ::strdup(symbolName);
                info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
                // string is owned by _undefines
                _undefines[info.name] = info;
            }
        }
        // third slot in __OBJC,__class is pointer to class name
        std::string className;
         if (objcClassNameFromExpression(c->getOperand(2), className)) {
            const char* symbolName = ::strdup(className.c_str());
            NameAndAttributes info;
            info.name = symbolName;
            info.attributes = (lto_symbol_attributes)
                (LTO_SYMBOL_PERMISSIONS_DATA |
                 LTO_SYMBOL_DEFINITION_REGULAR | 
                 LTO_SYMBOL_SCOPE_DEFAULT);
            _symbols.push_back(info);
            _defines[info.name] = 1;
         }
    }
}


// parse i386/ppc ObjC category data structure 
void LTOModule::addObjCCategory(GlobalVariable* clgv)
{
    if (ConstantStruct* c = dyn_cast<ConstantStruct>(clgv->getInitializer())) {
        // second slot in __OBJC,__category is pointer to target class name
        std::string targetclassName;
        if (objcClassNameFromExpression(c->getOperand(1), targetclassName)) {
            NameAndAttributes info;
            if (_undefines.find(targetclassName.c_str()) == _undefines.end()) {
                const char* symbolName = ::strdup(targetclassName.c_str());
                info.name = ::strdup(symbolName);
                info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
                // string is owned by _undefines
               _undefines[info.name] = info;
            }
        }
    }
}


// parse i386/ppc ObjC class list data structure 
void LTOModule::addObjCClassRef(GlobalVariable* clgv)
{
    std::string targetclassName;
    if (objcClassNameFromExpression(clgv->getInitializer(), targetclassName)) {
        NameAndAttributes info;
        if (_undefines.find(targetclassName.c_str()) == _undefines.end()) {
            const char* symbolName = ::strdup(targetclassName.c_str());
            info.name = ::strdup(symbolName);
            info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
            // string is owned by _undefines
            _undefines[info.name] = info;
        }
    }
}


void LTOModule::addDefinedDataSymbol(GlobalValue* v, Mangler& mangler)
{    
    // add to list of defined symbols
    addDefinedSymbol(v, mangler, false); 

    // Special case i386/ppc ObjC data structures in magic sections:
    // The issue is that the old ObjC object format did some strange 
    // contortions to avoid real linker symbols.  For instance, the 
    // ObjC class data structure is allocated statically in the executable 
    // that defines that class.  That data structures contains a pointer to
    // its superclass.  But instead of just initializing that part of the 
    // struct to the address of its superclass, and letting the static and 
    // dynamic linkers do the rest, the runtime works by having that field
    // instead point to a C-string that is the name of the superclass. 
    // At runtime the objc initialization updates that pointer and sets 
    // it to point to the actual super class.  As far as the linker
    // knows it is just a pointer to a string.  But then someone wanted the 
    // linker to issue errors at build time if the superclass was not found.  
    // So they figured out a way in mach-o object format to use an absolute 
    // symbols (.objc_class_name_Foo = 0) and a floating reference 
    // (.reference .objc_class_name_Bar) to cause the linker into erroring when
    // a class was missing.   
    // The following synthesizes the implicit .objc_* symbols for the linker
    // from the ObjC data structures generated by the front end.
    if (v->hasSection() /* && isTargetDarwin */) {
        // special case if this data blob is an ObjC class definition
        if (v->getSection().compare(0, 15, "__OBJC,__class,") == 0) {
            if (GlobalVariable* gv = dyn_cast<GlobalVariable>(v)) {
                addObjCClass(gv);
            }
        }                        
    
        // special case if this data blob is an ObjC category definition
        else if (v->getSection().compare(0, 18, "__OBJC,__category,") == 0) {
            if (GlobalVariable* gv = dyn_cast<GlobalVariable>(v)) {
                addObjCCategory(gv);
            }
        }                        
        
        // special case if this data blob is the list of referenced classes
        else if (v->getSection().compare(0, 18, "__OBJC,__cls_refs,") == 0) {
            if (GlobalVariable* gv = dyn_cast<GlobalVariable>(v)) {
                addObjCClassRef(gv);
            }
        }                        
    }

    // add external symbols referenced by this data.
    for (unsigned count = 0, total = v->getNumOperands();
                                                count != total; ++count) {
        findExternalRefs(v->getOperand(count), mangler);
    }
}


void LTOModule::addDefinedSymbol(GlobalValue* def, Mangler &mangler, 
                                 bool isFunction)
{    
    // ignore all llvm.* symbols
    if (def->getName().startswith("llvm."))
        return;

    // string is owned by _defines
    const char* symbolName = ::strdup(mangler.getNameWithPrefix(def).c_str());

    // set alignment part log2() can have rounding errors
    uint32_t align = def->getAlignment();
    uint32_t attr = align ? CountTrailingZeros_32(def->getAlignment()) : 0;
    
    // set permissions part
    if (isFunction)
        attr |= LTO_SYMBOL_PERMISSIONS_CODE;
    else {
        GlobalVariable* gv = dyn_cast<GlobalVariable>(def);
        if (gv && gv->isConstant())
            attr |= LTO_SYMBOL_PERMISSIONS_RODATA;
        else
            attr |= LTO_SYMBOL_PERMISSIONS_DATA;
    }
    
    // set definition part 
    if (def->hasWeakLinkage() || def->hasLinkOnceLinkage()) {
        attr |= LTO_SYMBOL_DEFINITION_WEAK;
    }
    else if (def->hasCommonLinkage()) {
        attr |= LTO_SYMBOL_DEFINITION_TENTATIVE;
    }
    else { 
        attr |= LTO_SYMBOL_DEFINITION_REGULAR;
    }
    
    // set scope part
    if (def->hasHiddenVisibility())
        attr |= LTO_SYMBOL_SCOPE_HIDDEN;
    else if (def->hasProtectedVisibility())
        attr |= LTO_SYMBOL_SCOPE_PROTECTED;
    else if (def->hasExternalLinkage() || def->hasWeakLinkage()
             || def->hasLinkOnceLinkage() || def->hasCommonLinkage())
        attr |= LTO_SYMBOL_SCOPE_DEFAULT;
    else
        attr |= LTO_SYMBOL_SCOPE_INTERNAL;

    // add to table of symbols
    NameAndAttributes info;
    info.name = symbolName;
    info.attributes = (lto_symbol_attributes)attr;
    _symbols.push_back(info);
    _defines[info.name] = 1;
}

void LTOModule::addAsmGlobalSymbol(const char *name) {
    // only add new define if not already defined
    if (_defines.count(name)) 
        return;
        
    // string is owned by _defines
    const char *symbolName = ::strdup(name);
    uint32_t attr = LTO_SYMBOL_DEFINITION_REGULAR;
    attr |= LTO_SYMBOL_SCOPE_DEFAULT;
    NameAndAttributes info;
    info.name = symbolName;
    info.attributes = (lto_symbol_attributes)attr;
    _symbols.push_back(info);
    _defines[info.name] = 1;
}

void LTOModule::addPotentialUndefinedSymbol(GlobalValue* decl, Mangler &mangler)
{   
    // ignore all llvm.* symbols
    if (decl->getName().startswith("llvm."))
        return;

    // ignore all aliases
    if (isa<GlobalAlias>(decl))
        return;

    std::string name = mangler.getNameWithPrefix(decl);

    // we already have the symbol
    if (_undefines.find(name) != _undefines.end())
      return;

    NameAndAttributes info;
    // string is owned by _undefines
    info.name = ::strdup(name.c_str());
    if (decl->hasExternalWeakLinkage())
      info.attributes = LTO_SYMBOL_DEFINITION_WEAKUNDEF;
    else
      info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
    _undefines[name] = info;
}



// Find external symbols referenced by VALUE. This is a recursive function.
void LTOModule::findExternalRefs(Value* value, Mangler &mangler) {

    if (GlobalValue* gv = dyn_cast<GlobalValue>(value)) {
        if (!gv->hasExternalLinkage())
            addPotentialUndefinedSymbol(gv, mangler);
        // If this is a variable definition, do not recursively process
        // initializer.  It might contain a reference to this variable
        // and cause an infinite loop.  The initializer will be
        // processed in addDefinedDataSymbol(). 
        return;
    }

    // GlobalValue, even with InternalLinkage type, may have operands with 
    // ExternalLinkage type. Do not ignore these operands.
    if (Constant* c = dyn_cast<Constant>(value)) {
        // Handle ConstantExpr, ConstantStruct, ConstantArry etc.
        for (unsigned i = 0, e = c->getNumOperands(); i != e; ++i)
            findExternalRefs(c->getOperand(i), mangler);
    }
}

void LTOModule::lazyParseSymbols()
{
    if (!_symbolsParsed) {
        _symbolsParsed = true;
        
        // Use mangler to add GlobalPrefix to names to match linker names.
        MCContext Context(*_target->getMCAsmInfo());
        Mangler mangler(Context, *_target->getTargetData());

        // add functions
        for (Module::iterator f = _module->begin(); f != _module->end(); ++f) {
            if (f->isDeclaration())
                addPotentialUndefinedSymbol(f, mangler);
            else 
                addDefinedFunctionSymbol(f, mangler);
        }
        
        // add data 
        for (Module::global_iterator v = _module->global_begin(), 
                                    e = _module->global_end(); v !=  e; ++v) {
            if (v->isDeclaration())
                addPotentialUndefinedSymbol(v, mangler);
            else 
                addDefinedDataSymbol(v, mangler);
        }

        // add asm globals
        const std::string &inlineAsm = _module->getModuleInlineAsm();
        const std::string glbl = ".globl";
        std::string asmSymbolName;
        std::string::size_type pos = inlineAsm.find(glbl, 0);
        while (pos != std::string::npos) {
          // eat .globl
          pos = pos + 6;

          // skip white space between .globl and symbol name
          std::string::size_type pbegin = inlineAsm.find_first_not_of(' ', pos);
          if (pbegin == std::string::npos)
            break;

          // find end-of-line
          std::string::size_type pend = inlineAsm.find_first_of('\n', pbegin);
          if (pend == std::string::npos)
            break;

          asmSymbolName.assign(inlineAsm, pbegin, pend - pbegin);
          addAsmGlobalSymbol(asmSymbolName.c_str());

          // search next .globl
          pos = inlineAsm.find(glbl, pend);
        }

        // make symbols for all undefines
        for (StringMap<NameAndAttributes>::iterator it=_undefines.begin(); 
                                                it != _undefines.end(); ++it) {
            // if this symbol also has a definition, then don't make an undefine
            // because it is a tentative definition
            if (_defines.count(it->getKey()) == 0) {
              NameAndAttributes info = it->getValue();
              _symbols.push_back(info);
            }
        }
    }    
}


uint32_t LTOModule::getSymbolCount()
{
    lazyParseSymbols();
    return _symbols.size();
}


lto_symbol_attributes LTOModule::getSymbolAttributes(uint32_t index)
{
    lazyParseSymbols();
    if (index < _symbols.size())
        return _symbols[index].attributes;
    else
        return lto_symbol_attributes(0);
}

const char* LTOModule::getSymbolName(uint32_t index)
{
    lazyParseSymbols();
    if (index < _symbols.size())
        return _symbols[index].name;
    else
        return NULL;
}