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llvm-project/llvm/lib/Target/BPF/BPFAbstractMemberAccess.cpp

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//===------ BPFAbstractMemberAccess.cpp - Abstracting Member Accesses -----===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This pass abstracted struct/union member accesses in order to support
// compile-once run-everywhere (CO-RE). The CO-RE intends to compile the program
// which can run on different kernels. In particular, if bpf program tries to
// access a particular kernel data structure member, the details of the
// intermediate member access will be remembered so bpf loader can do
// necessary adjustment right before program loading.
//
// For example,
//
// struct s {
// int a;
// int b;
// };
// struct t {
// struct s c;
// int d;
// };
// struct t e;
//
// For the member access e.c.b, the compiler will generate code
// &e + 4
//
// The compile-once run-everywhere instead generates the following code
// r = 4
// &e + r
// The "4" in "r = 4" can be changed based on a particular kernel version.
// For example, on a particular kernel version, if struct s is changed to
//
// struct s {
// int new_field;
// int a;
// int b;
// }
//
// By repeating the member access on the host, the bpf loader can
// adjust "r = 4" as "r = 8".
//
// This feature relies on the following three intrinsic calls:
// addr = preserve_array_access_index(base, dimension, index)
// addr = preserve_union_access_index(base, di_index)
// !llvm.preserve.access.index <union_ditype>
// addr = preserve_struct_access_index(base, gep_index, di_index)
// !llvm.preserve.access.index <struct_ditype>
//
// Bitfield member access needs special attention. User cannot take the
// address of a bitfield acceess. To facilitate kernel verifier
// for easy bitfield code optimization, a new clang intrinsic is introduced:
// uint32_t __builtin_preserve_field_info(member_access, info_kind)
// In IR, a chain with two (or more) intrinsic calls will be generated:
// ...
// addr = preserve_struct_access_index(base, 1, 1) !struct s
// uint32_t result = bpf_preserve_field_info(addr, info_kind)
//
// Suppose the info_kind is FIELD_SIGNEDNESS,
// The above two IR intrinsics will be replaced with
// a relocatable insn:
// signness = /* signness of member_access */
// and signness can be changed by bpf loader based on the
// types on the host.
//
// User can also test whether a field exists or not with
// uint32_t result = bpf_preserve_field_info(member_access, FIELD_EXISTENCE)
// The field will be always available (result = 1) during initial
// compilation, but bpf loader can patch with the correct value
// on the target host where the member_access may or may not be available
//
//===----------------------------------------------------------------------===//
#include "BPF.h"
#include "BPFCORE.h"
#include "BPFTargetMachine.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include <stack>
#define DEBUG_TYPE "bpf-abstract-member-access"
namespace llvm {
constexpr StringRef BPFCoreSharedInfo::AmaAttr;
} // namespace llvm
using namespace llvm;
namespace {
class BPFAbstractMemberAccess final : public ModulePass {
StringRef getPassName() const override {
return "BPF Abstract Member Access";
}
bool runOnModule(Module &M) override;
public:
static char ID;
TargetMachine *TM;
// Add optional BPFTargetMachine parameter so that BPF backend can add the phase
// with target machine to find out the endianness. The default constructor (without
// parameters) is used by the pass manager for managing purposes.
BPFAbstractMemberAccess(BPFTargetMachine *TM = nullptr) : ModulePass(ID), TM(TM) {}
struct CallInfo {
uint32_t Kind;
uint32_t AccessIndex;
Align RecordAlignment;
MDNode *Metadata;
Value *Base;
};
typedef std::stack<std::pair<CallInst *, CallInfo>> CallInfoStack;
private:
enum : uint32_t {
BPFPreserveArrayAI = 1,
BPFPreserveUnionAI = 2,
BPFPreserveStructAI = 3,
BPFPreserveFieldInfoAI = 4,
};
const DataLayout *DL = nullptr;
std::map<std::string, GlobalVariable *> GEPGlobals;
// A map to link preserve_*_access_index instrinsic calls.
std::map<CallInst *, std::pair<CallInst *, CallInfo>> AIChain;
// A map to hold all the base preserve_*_access_index instrinsic calls.
// The base call is not an input of any other preserve_*
// intrinsics.
std::map<CallInst *, CallInfo> BaseAICalls;
bool doTransformation(Module &M);
void traceAICall(CallInst *Call, CallInfo &ParentInfo);
void traceBitCast(BitCastInst *BitCast, CallInst *Parent,
CallInfo &ParentInfo);
void traceGEP(GetElementPtrInst *GEP, CallInst *Parent,
CallInfo &ParentInfo);
void collectAICallChains(Module &M, Function &F);
bool IsPreserveDIAccessIndexCall(const CallInst *Call, CallInfo &Cinfo);
bool IsValidAIChain(const MDNode *ParentMeta, uint32_t ParentAI,
const MDNode *ChildMeta);
bool removePreserveAccessIndexIntrinsic(Module &M);
void replaceWithGEP(std::vector<CallInst *> &CallList,
uint32_t NumOfZerosIndex, uint32_t DIIndex);
bool HasPreserveFieldInfoCall(CallInfoStack &CallStack);
void GetStorageBitRange(DIDerivedType *MemberTy, Align RecordAlignment,
uint32_t &StartBitOffset, uint32_t &EndBitOffset);
uint32_t GetFieldInfo(uint32_t InfoKind, DICompositeType *CTy,
uint32_t AccessIndex, uint32_t PatchImm,
Align RecordAlignment);
Value *computeBaseAndAccessKey(CallInst *Call, CallInfo &CInfo,
std::string &AccessKey, MDNode *&BaseMeta);
uint64_t getConstant(const Value *IndexValue);
bool transformGEPChain(Module &M, CallInst *Call, CallInfo &CInfo);
};
} // End anonymous namespace
char BPFAbstractMemberAccess::ID = 0;
INITIALIZE_PASS(BPFAbstractMemberAccess, DEBUG_TYPE,
"abstracting struct/union member accessees", false, false)
ModulePass *llvm::createBPFAbstractMemberAccess(BPFTargetMachine *TM) {
return new BPFAbstractMemberAccess(TM);
}
bool BPFAbstractMemberAccess::runOnModule(Module &M) {
LLVM_DEBUG(dbgs() << "********** Abstract Member Accesses **********\n");
// Bail out if no debug info.
if (M.debug_compile_units().empty())
return false;
DL = &M.getDataLayout();
return doTransformation(M);
}
static bool SkipDIDerivedTag(unsigned Tag, bool skipTypedef) {
if (Tag != dwarf::DW_TAG_typedef && Tag != dwarf::DW_TAG_const_type &&
Tag != dwarf::DW_TAG_volatile_type &&
Tag != dwarf::DW_TAG_restrict_type &&
Tag != dwarf::DW_TAG_member)
return false;
if (Tag == dwarf::DW_TAG_typedef && !skipTypedef)
return false;
return true;
}
static DIType * stripQualifiers(DIType *Ty, bool skipTypedef = true) {
while (auto *DTy = dyn_cast<DIDerivedType>(Ty)) {
if (!SkipDIDerivedTag(DTy->getTag(), skipTypedef))
break;
Ty = DTy->getBaseType();
}
return Ty;
}
static const DIType * stripQualifiers(const DIType *Ty) {
while (auto *DTy = dyn_cast<DIDerivedType>(Ty)) {
if (!SkipDIDerivedTag(DTy->getTag(), true))
break;
Ty = DTy->getBaseType();
}
return Ty;
}
static uint32_t calcArraySize(const DICompositeType *CTy, uint32_t StartDim) {
DINodeArray Elements = CTy->getElements();
uint32_t DimSize = 1;
for (uint32_t I = StartDim; I < Elements.size(); ++I) {
if (auto *Element = dyn_cast_or_null<DINode>(Elements[I]))
if (Element->getTag() == dwarf::DW_TAG_subrange_type) {
const DISubrange *SR = cast<DISubrange>(Element);
auto *CI = SR->getCount().dyn_cast<ConstantInt *>();
DimSize *= CI->getSExtValue();
}
}
return DimSize;
}
/// Check whether a call is a preserve_*_access_index intrinsic call or not.
bool BPFAbstractMemberAccess::IsPreserveDIAccessIndexCall(const CallInst *Call,
CallInfo &CInfo) {
if (!Call)
return false;
const auto *GV = dyn_cast<GlobalValue>(Call->getCalledOperand());
if (!GV)
return false;
if (GV->getName().startswith("llvm.preserve.array.access.index")) {
CInfo.Kind = BPFPreserveArrayAI;
CInfo.Metadata = Call->getMetadata(LLVMContext::MD_preserve_access_index);
if (!CInfo.Metadata)
report_fatal_error("Missing metadata for llvm.preserve.array.access.index intrinsic");
CInfo.AccessIndex = getConstant(Call->getArgOperand(2));
CInfo.Base = Call->getArgOperand(0);
CInfo.RecordAlignment =
DL->getABITypeAlign(CInfo.Base->getType()->getPointerElementType());
return true;
}
if (GV->getName().startswith("llvm.preserve.union.access.index")) {
CInfo.Kind = BPFPreserveUnionAI;
CInfo.Metadata = Call->getMetadata(LLVMContext::MD_preserve_access_index);
if (!CInfo.Metadata)
report_fatal_error("Missing metadata for llvm.preserve.union.access.index intrinsic");
CInfo.AccessIndex = getConstant(Call->getArgOperand(1));
CInfo.Base = Call->getArgOperand(0);
CInfo.RecordAlignment =
DL->getABITypeAlign(CInfo.Base->getType()->getPointerElementType());
return true;
}
if (GV->getName().startswith("llvm.preserve.struct.access.index")) {
CInfo.Kind = BPFPreserveStructAI;
CInfo.Metadata = Call->getMetadata(LLVMContext::MD_preserve_access_index);
if (!CInfo.Metadata)
report_fatal_error("Missing metadata for llvm.preserve.struct.access.index intrinsic");
CInfo.AccessIndex = getConstant(Call->getArgOperand(2));
CInfo.Base = Call->getArgOperand(0);
CInfo.RecordAlignment =
DL->getABITypeAlign(CInfo.Base->getType()->getPointerElementType());
return true;
}
if (GV->getName().startswith("llvm.bpf.preserve.field.info")) {
CInfo.Kind = BPFPreserveFieldInfoAI;
CInfo.Metadata = nullptr;
// Check validity of info_kind as clang did not check this.
uint64_t InfoKind = getConstant(Call->getArgOperand(1));
if (InfoKind >= BPFCoreSharedInfo::MAX_FIELD_RELOC_KIND)
report_fatal_error("Incorrect info_kind for llvm.bpf.preserve.field.info intrinsic");
CInfo.AccessIndex = InfoKind;
return true;
}
return false;
}
void BPFAbstractMemberAccess::replaceWithGEP(std::vector<CallInst *> &CallList,
uint32_t DimensionIndex,
uint32_t GEPIndex) {
for (auto Call : CallList) {
uint32_t Dimension = 1;
if (DimensionIndex > 0)
Dimension = getConstant(Call->getArgOperand(DimensionIndex));
Constant *Zero =
ConstantInt::get(Type::getInt32Ty(Call->getParent()->getContext()), 0);
SmallVector<Value *, 4> IdxList;
for (unsigned I = 0; I < Dimension; ++I)
IdxList.push_back(Zero);
IdxList.push_back(Call->getArgOperand(GEPIndex));
auto *GEP = GetElementPtrInst::CreateInBounds(Call->getArgOperand(0),
IdxList, "", Call);
Call->replaceAllUsesWith(GEP);
Call->eraseFromParent();
}
}
bool BPFAbstractMemberAccess::removePreserveAccessIndexIntrinsic(Module &M) {
std::vector<CallInst *> PreserveArrayIndexCalls;
std::vector<CallInst *> PreserveUnionIndexCalls;
std::vector<CallInst *> PreserveStructIndexCalls;
bool Found = false;
for (Function &F : M)
for (auto &BB : F)
for (auto &I : BB) {
auto *Call = dyn_cast<CallInst>(&I);
CallInfo CInfo;
if (!IsPreserveDIAccessIndexCall(Call, CInfo))
continue;
Found = true;
if (CInfo.Kind == BPFPreserveArrayAI)
PreserveArrayIndexCalls.push_back(Call);
else if (CInfo.Kind == BPFPreserveUnionAI)
PreserveUnionIndexCalls.push_back(Call);
else
PreserveStructIndexCalls.push_back(Call);
}
// do the following transformation:
// . addr = preserve_array_access_index(base, dimension, index)
// is transformed to
// addr = GEP(base, dimenion's zero's, index)
// . addr = preserve_union_access_index(base, di_index)
// is transformed to
// addr = base, i.e., all usages of "addr" are replaced by "base".
// . addr = preserve_struct_access_index(base, gep_index, di_index)
// is transformed to
// addr = GEP(base, 0, gep_index)
replaceWithGEP(PreserveArrayIndexCalls, 1, 2);
replaceWithGEP(PreserveStructIndexCalls, 0, 1);
for (auto Call : PreserveUnionIndexCalls) {
Call->replaceAllUsesWith(Call->getArgOperand(0));
Call->eraseFromParent();
}
return Found;
}
/// Check whether the access index chain is valid. We check
/// here because there may be type casts between two
/// access indexes. We want to ensure memory access still valid.
bool BPFAbstractMemberAccess::IsValidAIChain(const MDNode *ParentType,
uint32_t ParentAI,
const MDNode *ChildType) {
if (!ChildType)
return true; // preserve_field_info, no type comparison needed.
const DIType *PType = stripQualifiers(cast<DIType>(ParentType));
const DIType *CType = stripQualifiers(cast<DIType>(ChildType));
// Child is a derived/pointer type, which is due to type casting.
// Pointer type cannot be in the middle of chain.
if (isa<DIDerivedType>(CType))
return false;
// Parent is a pointer type.
if (const auto *PtrTy = dyn_cast<DIDerivedType>(PType)) {
if (PtrTy->getTag() != dwarf::DW_TAG_pointer_type)
return false;
return stripQualifiers(PtrTy->getBaseType()) == CType;
}
// Otherwise, struct/union/array types
const auto *PTy = dyn_cast<DICompositeType>(PType);
const auto *CTy = dyn_cast<DICompositeType>(CType);
assert(PTy && CTy && "ParentType or ChildType is null or not composite");
uint32_t PTyTag = PTy->getTag();
assert(PTyTag == dwarf::DW_TAG_array_type ||
PTyTag == dwarf::DW_TAG_structure_type ||
PTyTag == dwarf::DW_TAG_union_type);
uint32_t CTyTag = CTy->getTag();
assert(CTyTag == dwarf::DW_TAG_array_type ||
CTyTag == dwarf::DW_TAG_structure_type ||
CTyTag == dwarf::DW_TAG_union_type);
// Multi dimensional arrays, base element should be the same
if (PTyTag == dwarf::DW_TAG_array_type && PTyTag == CTyTag)
return PTy->getBaseType() == CTy->getBaseType();
DIType *Ty;
if (PTyTag == dwarf::DW_TAG_array_type)
Ty = PTy->getBaseType();
else
Ty = dyn_cast<DIType>(PTy->getElements()[ParentAI]);
return dyn_cast<DICompositeType>(stripQualifiers(Ty)) == CTy;
}
void BPFAbstractMemberAccess::traceAICall(CallInst *Call,
CallInfo &ParentInfo) {
for (User *U : Call->users()) {
Instruction *Inst = dyn_cast<Instruction>(U);
if (!Inst)
continue;
if (auto *BI = dyn_cast<BitCastInst>(Inst)) {
traceBitCast(BI, Call, ParentInfo);
} else if (auto *CI = dyn_cast<CallInst>(Inst)) {
CallInfo ChildInfo;
if (IsPreserveDIAccessIndexCall(CI, ChildInfo) &&
IsValidAIChain(ParentInfo.Metadata, ParentInfo.AccessIndex,
ChildInfo.Metadata)) {
AIChain[CI] = std::make_pair(Call, ParentInfo);
traceAICall(CI, ChildInfo);
} else {
BaseAICalls[Call] = ParentInfo;
}
} else if (auto *GI = dyn_cast<GetElementPtrInst>(Inst)) {
if (GI->hasAllZeroIndices())
traceGEP(GI, Call, ParentInfo);
else
BaseAICalls[Call] = ParentInfo;
} else {
BaseAICalls[Call] = ParentInfo;
}
}
}
void BPFAbstractMemberAccess::traceBitCast(BitCastInst *BitCast,
CallInst *Parent,
CallInfo &ParentInfo) {
for (User *U : BitCast->users()) {
Instruction *Inst = dyn_cast<Instruction>(U);
if (!Inst)
continue;
if (auto *BI = dyn_cast<BitCastInst>(Inst)) {
traceBitCast(BI, Parent, ParentInfo);
} else if (auto *CI = dyn_cast<CallInst>(Inst)) {
CallInfo ChildInfo;
if (IsPreserveDIAccessIndexCall(CI, ChildInfo) &&
IsValidAIChain(ParentInfo.Metadata, ParentInfo.AccessIndex,
ChildInfo.Metadata)) {
AIChain[CI] = std::make_pair(Parent, ParentInfo);
traceAICall(CI, ChildInfo);
} else {
BaseAICalls[Parent] = ParentInfo;
}
} else if (auto *GI = dyn_cast<GetElementPtrInst>(Inst)) {
if (GI->hasAllZeroIndices())
traceGEP(GI, Parent, ParentInfo);
else
BaseAICalls[Parent] = ParentInfo;
} else {
BaseAICalls[Parent] = ParentInfo;
}
}
}
void BPFAbstractMemberAccess::traceGEP(GetElementPtrInst *GEP, CallInst *Parent,
CallInfo &ParentInfo) {
for (User *U : GEP->users()) {
Instruction *Inst = dyn_cast<Instruction>(U);
if (!Inst)
continue;
if (auto *BI = dyn_cast<BitCastInst>(Inst)) {
traceBitCast(BI, Parent, ParentInfo);
} else if (auto *CI = dyn_cast<CallInst>(Inst)) {
CallInfo ChildInfo;
if (IsPreserveDIAccessIndexCall(CI, ChildInfo) &&
IsValidAIChain(ParentInfo.Metadata, ParentInfo.AccessIndex,
ChildInfo.Metadata)) {
AIChain[CI] = std::make_pair(Parent, ParentInfo);
traceAICall(CI, ChildInfo);
} else {
BaseAICalls[Parent] = ParentInfo;
}
} else if (auto *GI = dyn_cast<GetElementPtrInst>(Inst)) {
if (GI->hasAllZeroIndices())
traceGEP(GI, Parent, ParentInfo);
else
BaseAICalls[Parent] = ParentInfo;
} else {
BaseAICalls[Parent] = ParentInfo;
}
}
}
void BPFAbstractMemberAccess::collectAICallChains(Module &M, Function &F) {
AIChain.clear();
BaseAICalls.clear();
for (auto &BB : F)
for (auto &I : BB) {
CallInfo CInfo;
auto *Call = dyn_cast<CallInst>(&I);
if (!IsPreserveDIAccessIndexCall(Call, CInfo) ||
AIChain.find(Call) != AIChain.end())
continue;
traceAICall(Call, CInfo);
}
}
uint64_t BPFAbstractMemberAccess::getConstant(const Value *IndexValue) {
const ConstantInt *CV = dyn_cast<ConstantInt>(IndexValue);
assert(CV);
return CV->getValue().getZExtValue();
}
/// Get the start and the end of storage offset for \p MemberTy.
void BPFAbstractMemberAccess::GetStorageBitRange(DIDerivedType *MemberTy,
Align RecordAlignment,
uint32_t &StartBitOffset,
uint32_t &EndBitOffset) {
uint32_t MemberBitSize = MemberTy->getSizeInBits();
uint32_t MemberBitOffset = MemberTy->getOffsetInBits();
uint32_t AlignBits = RecordAlignment.value() * 8;
if (RecordAlignment > 8 || MemberBitSize > AlignBits)
report_fatal_error("Unsupported field expression for llvm.bpf.preserve.field.info, "
"requiring too big alignment");
StartBitOffset = MemberBitOffset & ~(AlignBits - 1);
if ((StartBitOffset + AlignBits) < (MemberBitOffset + MemberBitSize))
report_fatal_error("Unsupported field expression for llvm.bpf.preserve.field.info, "
"cross alignment boundary");
EndBitOffset = StartBitOffset + AlignBits;
}
uint32_t BPFAbstractMemberAccess::GetFieldInfo(uint32_t InfoKind,
DICompositeType *CTy,
uint32_t AccessIndex,
uint32_t PatchImm,
Align RecordAlignment) {
if (InfoKind == BPFCoreSharedInfo::FIELD_EXISTENCE)
return 1;
uint32_t Tag = CTy->getTag();
if (InfoKind == BPFCoreSharedInfo::FIELD_BYTE_OFFSET) {
if (Tag == dwarf::DW_TAG_array_type) {
auto *EltTy = stripQualifiers(CTy->getBaseType());
PatchImm += AccessIndex * calcArraySize(CTy, 1) *
(EltTy->getSizeInBits() >> 3);
} else if (Tag == dwarf::DW_TAG_structure_type) {
auto *MemberTy = cast<DIDerivedType>(CTy->getElements()[AccessIndex]);
if (!MemberTy->isBitField()) {
PatchImm += MemberTy->getOffsetInBits() >> 3;
} else {
unsigned SBitOffset, NextSBitOffset;
GetStorageBitRange(MemberTy, RecordAlignment, SBitOffset,
NextSBitOffset);
PatchImm += SBitOffset >> 3;
}
}
return PatchImm;
}
if (InfoKind == BPFCoreSharedInfo::FIELD_BYTE_SIZE) {
if (Tag == dwarf::DW_TAG_array_type) {
auto *EltTy = stripQualifiers(CTy->getBaseType());
return calcArraySize(CTy, 1) * (EltTy->getSizeInBits() >> 3);
} else {
auto *MemberTy = cast<DIDerivedType>(CTy->getElements()[AccessIndex]);
uint32_t SizeInBits = MemberTy->getSizeInBits();
if (!MemberTy->isBitField())
return SizeInBits >> 3;
unsigned SBitOffset, NextSBitOffset;
GetStorageBitRange(MemberTy, RecordAlignment, SBitOffset, NextSBitOffset);
SizeInBits = NextSBitOffset - SBitOffset;
if (SizeInBits & (SizeInBits - 1))
report_fatal_error("Unsupported field expression for llvm.bpf.preserve.field.info");
return SizeInBits >> 3;
}
}
if (InfoKind == BPFCoreSharedInfo::FIELD_SIGNEDNESS) {
const DIType *BaseTy;
if (Tag == dwarf::DW_TAG_array_type) {
// Signedness only checked when final array elements are accessed.
if (CTy->getElements().size() != 1)
report_fatal_error("Invalid array expression for llvm.bpf.preserve.field.info");
BaseTy = stripQualifiers(CTy->getBaseType());
} else {
auto *MemberTy = cast<DIDerivedType>(CTy->getElements()[AccessIndex]);
BaseTy = stripQualifiers(MemberTy->getBaseType());
}
// Only basic types and enum types have signedness.
const auto *BTy = dyn_cast<DIBasicType>(BaseTy);
while (!BTy) {
const auto *CompTy = dyn_cast<DICompositeType>(BaseTy);
// Report an error if the field expression does not have signedness.
if (!CompTy || CompTy->getTag() != dwarf::DW_TAG_enumeration_type)
report_fatal_error("Invalid field expression for llvm.bpf.preserve.field.info");
BaseTy = stripQualifiers(CompTy->getBaseType());
BTy = dyn_cast<DIBasicType>(BaseTy);
}
uint32_t Encoding = BTy->getEncoding();
return (Encoding == dwarf::DW_ATE_signed || Encoding == dwarf::DW_ATE_signed_char);
}
if (InfoKind == BPFCoreSharedInfo::FIELD_LSHIFT_U64) {
// The value is loaded into a value with FIELD_BYTE_SIZE size,
// and then zero or sign extended to U64.
// FIELD_LSHIFT_U64 and FIELD_RSHIFT_U64 are operations
// to extract the original value.
const Triple &Triple = TM->getTargetTriple();
DIDerivedType *MemberTy = nullptr;
bool IsBitField = false;
uint32_t SizeInBits;
if (Tag == dwarf::DW_TAG_array_type) {
auto *EltTy = stripQualifiers(CTy->getBaseType());
SizeInBits = calcArraySize(CTy, 1) * EltTy->getSizeInBits();
} else {
MemberTy = cast<DIDerivedType>(CTy->getElements()[AccessIndex]);
SizeInBits = MemberTy->getSizeInBits();
IsBitField = MemberTy->isBitField();
}
if (!IsBitField) {
if (SizeInBits > 64)
report_fatal_error("too big field size for llvm.bpf.preserve.field.info");
return 64 - SizeInBits;
}
unsigned SBitOffset, NextSBitOffset;
GetStorageBitRange(MemberTy, RecordAlignment, SBitOffset, NextSBitOffset);
if (NextSBitOffset - SBitOffset > 64)
report_fatal_error("too big field size for llvm.bpf.preserve.field.info");
unsigned OffsetInBits = MemberTy->getOffsetInBits();
if (Triple.getArch() == Triple::bpfel)
return SBitOffset + 64 - OffsetInBits - SizeInBits;
else
return OffsetInBits + 64 - NextSBitOffset;
}
if (InfoKind == BPFCoreSharedInfo::FIELD_RSHIFT_U64) {
DIDerivedType *MemberTy = nullptr;
bool IsBitField = false;
uint32_t SizeInBits;
if (Tag == dwarf::DW_TAG_array_type) {
auto *EltTy = stripQualifiers(CTy->getBaseType());
SizeInBits = calcArraySize(CTy, 1) * EltTy->getSizeInBits();
} else {
MemberTy = cast<DIDerivedType>(CTy->getElements()[AccessIndex]);
SizeInBits = MemberTy->getSizeInBits();
IsBitField = MemberTy->isBitField();
}
if (!IsBitField) {
if (SizeInBits > 64)
report_fatal_error("too big field size for llvm.bpf.preserve.field.info");
return 64 - SizeInBits;
}
unsigned SBitOffset, NextSBitOffset;
GetStorageBitRange(MemberTy, RecordAlignment, SBitOffset, NextSBitOffset);
if (NextSBitOffset - SBitOffset > 64)
report_fatal_error("too big field size for llvm.bpf.preserve.field.info");
return 64 - SizeInBits;
}
llvm_unreachable("Unknown llvm.bpf.preserve.field.info info kind");
}
bool BPFAbstractMemberAccess::HasPreserveFieldInfoCall(CallInfoStack &CallStack) {
// This is called in error return path, no need to maintain CallStack.
while (CallStack.size()) {
auto StackElem = CallStack.top();
if (StackElem.second.Kind == BPFPreserveFieldInfoAI)
return true;
CallStack.pop();
}
return false;
}
/// Compute the base of the whole preserve_* intrinsics chains, i.e., the base
/// pointer of the first preserve_*_access_index call, and construct the access
/// string, which will be the name of a global variable.
Value *BPFAbstractMemberAccess::computeBaseAndAccessKey(CallInst *Call,
CallInfo &CInfo,
std::string &AccessKey,
MDNode *&TypeMeta) {
Value *Base = nullptr;
std::string TypeName;
CallInfoStack CallStack;
// Put the access chain into a stack with the top as the head of the chain.
while (Call) {
CallStack.push(std::make_pair(Call, CInfo));
CInfo = AIChain[Call].second;
Call = AIChain[Call].first;
}
// The access offset from the base of the head of chain is also
// calculated here as all debuginfo types are available.
// Get type name and calculate the first index.
// We only want to get type name from typedef, structure or union.
// If user wants a relocation like
// int *p; ... __builtin_preserve_access_index(&p[4]) ...
// or
// int a[10][20]; ... __builtin_preserve_access_index(&a[2][3]) ...
// we will skip them.
uint32_t FirstIndex = 0;
uint32_t PatchImm = 0; // AccessOffset or the requested field info
uint32_t InfoKind = BPFCoreSharedInfo::FIELD_BYTE_OFFSET;
while (CallStack.size()) {
auto StackElem = CallStack.top();
Call = StackElem.first;
CInfo = StackElem.second;
if (!Base)
Base = CInfo.Base;
DIType *PossibleTypeDef = stripQualifiers(cast<DIType>(CInfo.Metadata),
false);
DIType *Ty = stripQualifiers(PossibleTypeDef);
if (CInfo.Kind == BPFPreserveUnionAI ||
CInfo.Kind == BPFPreserveStructAI) {
// struct or union type. If the typedef is in the metadata, always
// use the typedef.
TypeName = std::string(PossibleTypeDef->getName());
TypeMeta = PossibleTypeDef;
PatchImm += FirstIndex * (Ty->getSizeInBits() >> 3);
break;
}
assert(CInfo.Kind == BPFPreserveArrayAI);
// Array entries will always be consumed for accumulative initial index.
CallStack.pop();
// BPFPreserveArrayAI
uint64_t AccessIndex = CInfo.AccessIndex;
DIType *BaseTy = nullptr;
bool CheckElemType = false;
if (const auto *CTy = dyn_cast<DICompositeType>(Ty)) {
// array type
assert(CTy->getTag() == dwarf::DW_TAG_array_type);
FirstIndex += AccessIndex * calcArraySize(CTy, 1);
BaseTy = stripQualifiers(CTy->getBaseType());
CheckElemType = CTy->getElements().size() == 1;
} else {
// pointer type
auto *DTy = cast<DIDerivedType>(Ty);
assert(DTy->getTag() == dwarf::DW_TAG_pointer_type);
BaseTy = stripQualifiers(DTy->getBaseType());
CTy = dyn_cast<DICompositeType>(BaseTy);
if (!CTy) {
CheckElemType = true;
} else if (CTy->getTag() != dwarf::DW_TAG_array_type) {
FirstIndex += AccessIndex;
CheckElemType = true;
} else {
FirstIndex += AccessIndex * calcArraySize(CTy, 0);
}
}
if (CheckElemType) {
auto *CTy = dyn_cast<DICompositeType>(BaseTy);
if (!CTy) {
if (HasPreserveFieldInfoCall(CallStack))
report_fatal_error("Invalid field access for llvm.preserve.field.info intrinsic");
return nullptr;
}
unsigned CTag = CTy->getTag();
if (CTag == dwarf::DW_TAG_structure_type || CTag == dwarf::DW_TAG_union_type) {
TypeName = std::string(CTy->getName());
} else {
if (HasPreserveFieldInfoCall(CallStack))
report_fatal_error("Invalid field access for llvm.preserve.field.info intrinsic");
return nullptr;
}
TypeMeta = CTy;
PatchImm += FirstIndex * (CTy->getSizeInBits() >> 3);
break;
}
}
assert(TypeName.size());
AccessKey += std::to_string(FirstIndex);
// Traverse the rest of access chain to complete offset calculation
// and access key construction.
while (CallStack.size()) {
auto StackElem = CallStack.top();
CInfo = StackElem.second;
CallStack.pop();
if (CInfo.Kind == BPFPreserveFieldInfoAI) {
InfoKind = CInfo.AccessIndex;
break;
}
// If the next Call (the top of the stack) is a BPFPreserveFieldInfoAI,
// the action will be extracting field info.
if (CallStack.size()) {
auto StackElem2 = CallStack.top();
CallInfo CInfo2 = StackElem2.second;
if (CInfo2.Kind == BPFPreserveFieldInfoAI) {
InfoKind = CInfo2.AccessIndex;
assert(CallStack.size() == 1);
}
}
// Access Index
uint64_t AccessIndex = CInfo.AccessIndex;
AccessKey += ":" + std::to_string(AccessIndex);
MDNode *MDN = CInfo.Metadata;
// At this stage, it cannot be pointer type.
auto *CTy = cast<DICompositeType>(stripQualifiers(cast<DIType>(MDN)));
PatchImm = GetFieldInfo(InfoKind, CTy, AccessIndex, PatchImm,
CInfo.RecordAlignment);
}
// Access key is the
// "llvm." + type name + ":" + reloc type + ":" + patched imm + "$" +
// access string,
// uniquely identifying one relocation.
// The prefix "llvm." indicates this is a temporary global, which should
// not be emitted to ELF file.
AccessKey = "llvm." + TypeName + ":" + std::to_string(InfoKind) + ":" +
std::to_string(PatchImm) + "$" + AccessKey;
return Base;
}
/// Call/Kind is the base preserve_*_access_index() call. Attempts to do
/// transformation to a chain of relocable GEPs.
bool BPFAbstractMemberAccess::transformGEPChain(Module &M, CallInst *Call,
CallInfo &CInfo) {
std::string AccessKey;
MDNode *TypeMeta;
Value *Base =
computeBaseAndAccessKey(Call, CInfo, AccessKey, TypeMeta);
if (!Base)
return false;
BasicBlock *BB = Call->getParent();
GlobalVariable *GV;
if (GEPGlobals.find(AccessKey) == GEPGlobals.end()) {
IntegerType *VarType;
if (CInfo.Kind == BPFPreserveFieldInfoAI)
VarType = Type::getInt32Ty(BB->getContext()); // 32bit return value
else
VarType = Type::getInt64Ty(BB->getContext()); // 64bit ptr arith
GV = new GlobalVariable(M, VarType, false, GlobalVariable::ExternalLinkage,
NULL, AccessKey);
GV->addAttribute(BPFCoreSharedInfo::AmaAttr);
GV->setMetadata(LLVMContext::MD_preserve_access_index, TypeMeta);
GEPGlobals[AccessKey] = GV;
} else {
GV = GEPGlobals[AccessKey];
}
if (CInfo.Kind == BPFPreserveFieldInfoAI) {
// Load the global variable which represents the returned field info.
auto *LDInst = new LoadInst(Type::getInt32Ty(BB->getContext()), GV, "",
Call);
Call->replaceAllUsesWith(LDInst);
Call->eraseFromParent();
return true;
}
// For any original GEP Call and Base %2 like
// %4 = bitcast %struct.net_device** %dev1 to i64*
// it is transformed to:
// %6 = load sk_buff:50:$0:0:0:2:0
// %7 = bitcast %struct.sk_buff* %2 to i8*
// %8 = getelementptr i8, i8* %7, %6
// %9 = bitcast i8* %8 to i64*
// using %9 instead of %4
// The original Call inst is removed.
// Load the global variable.
auto *LDInst = new LoadInst(Type::getInt64Ty(BB->getContext()), GV, "", Call);
// Generate a BitCast
auto *BCInst = new BitCastInst(Base, Type::getInt8PtrTy(BB->getContext()));
BB->getInstList().insert(Call->getIterator(), BCInst);
// Generate a GetElementPtr
auto *GEP = GetElementPtrInst::Create(Type::getInt8Ty(BB->getContext()),
BCInst, LDInst);
BB->getInstList().insert(Call->getIterator(), GEP);
// Generate a BitCast
auto *BCInst2 = new BitCastInst(GEP, Call->getType());
BB->getInstList().insert(Call->getIterator(), BCInst2);
Call->replaceAllUsesWith(BCInst2);
Call->eraseFromParent();
return true;
}
bool BPFAbstractMemberAccess::doTransformation(Module &M) {
bool Transformed = false;
for (Function &F : M) {
// Collect PreserveDIAccessIndex Intrinsic call chains.
// The call chains will be used to generate the access
// patterns similar to GEP.
collectAICallChains(M, F);
for (auto &C : BaseAICalls)
Transformed = transformGEPChain(M, C.first, C.second) || Transformed;
}
return removePreserveAccessIndexIntrinsic(M) || Transformed;
}
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