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//===- StripAttributes.cpp - Remove attributes not supported by PNaCl------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass strips out attributes that are not supported by PNaCl's
// stable ABI. Currently, this strips out:
//
// * Function and argument attributes from functions and function
// calls.
// * Calling conventions from functions and function calls.
// * The "align" attribute on functions.
// * The alignment argument of memcpy/memmove/memset intrinsic calls.
// * The "unnamed_addr" attribute on functions and global variables.
// * The distinction between "internal" and "private" linkage.
// * "protected" and "internal" visibility of functions and globals.
// * The arithmetic attributes "nsw", "nuw" and "exact".
// * It reduces the set of possible "align" attributes on memory
// accesses.
//
//===----------------------------------------------------------------------===//
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/Pass.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Transforms/NaCl.h"
using namespace llvm;
namespace {
// This is a ModulePass so that it can modify attributes of global
// variables.
class StripAttributes : public ModulePass {
public:
static char ID; // Pass identification, replacement for typeid
StripAttributes() : ModulePass(ID) {
initializeStripAttributesPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnModule(Module &M);
};
}
char StripAttributes::ID = 0;
INITIALIZE_PASS(StripAttributes, "nacl-strip-attributes",
"Strip out attributes that are not part of PNaCl's ABI",
false, false)
// Most attributes are just hints which can safely be removed. A few
// attributes can break programs if removed, so check all attributes
// before removing them, in case LLVM adds new attributes.
static void CheckAttributes(AttributeSet Attrs) {
for (unsigned Slot = 0; Slot < Attrs.getNumSlots(); ++Slot) {
for (AttributeSet::iterator Attr = Attrs.begin(Slot), E = Attrs.end(Slot);
Attr != E; ++Attr) {
if (!Attr->isEnumAttribute()) {
continue;
}
switch (Attr->getKindAsEnum()) {
// The following attributes can affect calling conventions.
// Rather than complaining, we just strip these out.
// ExpandSmallArguments should have rendered SExt/ZExt
// meaningless since the function arguments will be at least
// 32-bit.
case Attribute::InReg:
case Attribute::SExt:
case Attribute::ZExt:
// These attributes influence ABI decisions that should not be
// visible to PNaCl pexes.
case Attribute::NonLazyBind: // Only relevant to dynamic linking.
case Attribute::NoRedZone:
case Attribute::StackAlignment:
// The following attributes are just hints, which can be
// safely removed.
case Attribute::AlwaysInline:
case Attribute::InlineHint:
case Attribute::MinSize:
case Attribute::NoAlias:
case Attribute::NoBuiltin:
case Attribute::NoCapture:
case Attribute::NoDuplicate:
case Attribute::NoImplicitFloat:
case Attribute::NoInline:
case Attribute::NoReturn:
case Attribute::OptimizeForSize:
case Attribute::ReadNone:
case Attribute::ReadOnly:
// PNaCl does not support -fstack-protector in the translator.
case Attribute::StackProtect:
case Attribute::StackProtectReq:
case Attribute::StackProtectStrong:
// PNaCl does not support ASan in the translator.
case Attribute::SanitizeAddress:
case Attribute::SanitizeThread:
case Attribute::SanitizeMemory:
// The Language References cites setjmp() as an example of a
// function which returns twice, and says ReturnsTwice is
// necessary to disable optimizations such as tail calls.
// However, in the PNaCl ABI, setjmp() is an intrinsic, and
// user-defined functions are not allowed to return twice.
case Attribute::ReturnsTwice:
// NoUnwind is not a hint if it causes unwind info to be
// omitted, since this will prevent C++ exceptions from
// propagating. In the future, when PNaCl supports zero-cost
// C++ exception handling using unwind info, we might allow
// NoUnwind and UWTable. Alternatively, we might continue to
// disallow them, and just generate unwind info for all
// functions.
case Attribute::NoUnwind:
case Attribute::UWTable:
break;
case Attribute::ByVal:
case Attribute::StructRet:
case Attribute::Alignment:
Attrs.dump();
report_fatal_error(
"Attribute should already have been removed by ExpandByVal");
case Attribute::Naked:
case Attribute::Nest:
Attrs.dump();
report_fatal_error("Unsupported attribute");
default:
Attrs.dump();
report_fatal_error("Unrecognized attribute");
}
}
}
}
void stripGlobalValueAttrs(GlobalValue *GV) {
// In case source code uses __attribute__((visibility("hidden"))) or
// __attribute__((visibility("protected"))), strip these attributes.
GV->setVisibility(GlobalValue::DefaultVisibility);
GV->setUnnamedAddr(false);
// Convert "private" linkage to "internal" to reduce the number of
// linkage types that need to be represented in PNaCl's wire format.
//
// We convert "private" to "internal" rather than vice versa because
// "private" symbols are omitted from the nexe's symbol table, which
// would get in the way of debugging when an unstripped pexe is
// translated offline.
if (GV->getLinkage() == GlobalValue::PrivateLinkage)
GV->setLinkage(GlobalValue::InternalLinkage);
}
static unsigned normalizeAlignment(DataLayout *DL, unsigned Alignment,
Type *Ty, bool IsAtomic) {
#if 0
unsigned MaxAllowed = 1;
if (Ty->isDoubleTy() || Ty->isFloatTy() || IsAtomic)
MaxAllowed = DL->getTypeAllocSize(Ty);
// If the alignment is set to 0, this means "use the default
// alignment for the target", which we fill in explicitly.
if (Alignment == 0 || Alignment >= MaxAllowed)
return MaxAllowed;
return 1;
#else
return Alignment; // EMSCRIPTEN: no need to change alignment
#endif
}
void stripFunctionAttrs(DataLayout *DL, Function *Func) {
CheckAttributes(Func->getAttributes());
Func->setAttributes(AttributeSet());
Func->setCallingConv(CallingConv::C);
Func->setAlignment(0);
for (Function::iterator BB = Func->begin(), E = Func->end();
BB != E; ++BB) {
for (BasicBlock::iterator Inst = BB->begin(), E = BB->end();
Inst != E; ++Inst) {
CallSite Call(Inst);
if (Call) {
CheckAttributes(Call.getAttributes());
Call.setAttributes(AttributeSet());
Call.setCallingConv(CallingConv::C);
#if 0 // EMSCRIPTEN: we do support alignment info in these calls
// Set memcpy(), memmove() and memset() to use pessimistic
// alignment assumptions.
if (MemIntrinsic *MemOp = dyn_cast<MemIntrinsic>(Inst)) {
Type *AlignTy = MemOp->getAlignmentCst()->getType();
MemOp->setAlignment(ConstantInt::get(AlignTy, 1));
}
#endif
} else if (OverflowingBinaryOperator *Op =
dyn_cast<OverflowingBinaryOperator>(Inst)) {
cast<BinaryOperator>(Op)->setHasNoUnsignedWrap(false);
cast<BinaryOperator>(Op)->setHasNoSignedWrap(false);
} else if (PossiblyExactOperator *Op =
dyn_cast<PossiblyExactOperator>(Inst)) {
cast<BinaryOperator>(Op)->setIsExact(false);
} else if (LoadInst *Load = dyn_cast<LoadInst>(Inst)) {
Load->setAlignment(normalizeAlignment(
DL, Load->getAlignment(),
Load->getType(),
Load->isAtomic()));
} else if (StoreInst *Store = dyn_cast<StoreInst>(Inst)) {
Store->setAlignment(normalizeAlignment(
DL, Store->getAlignment(),
Store->getValueOperand()->getType(),
Store->isAtomic()));
}
}
}
}
bool StripAttributes::runOnModule(Module &M) {
DataLayout DL(&M);
for (Module::iterator Func = M.begin(), E = M.end(); Func != E; ++Func) {
// Avoid stripping attributes from intrinsics because the
// constructor for Functions just adds them back again. It would
// be confusing if the attributes were sometimes present on
// intrinsics and sometimes not.
if (!Func->isIntrinsic()) {
stripGlobalValueAttrs(Func);
stripFunctionAttrs(&DL, Func);
}
}
for (Module::global_iterator GV = M.global_begin(), E = M.global_end();
GV != E; ++GV) {
stripGlobalValueAttrs(GV);
}
return true;
}
ModulePass *llvm::createStripAttributesPass() {
return new StripAttributes();
}
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