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llvm-project/llvm/lib/Target/BPF/BPFAbstractMemberAccess.cpp
Yonghong Song 98e2274458 [BPF] fix a CO-RE bitfield relocation error with >8 record alignment 
Jussi Maki reported a fatal error like below for a bitfield
CO-RE relocation:
  fatal error: error in backend: Unsupported field expression for
  llvm.bpf.preserve.field.info, requiring too big alignment
The failure is related to kernel struct thread_struct. The following
is a simplied example.

Suppose we have below structure:
  struct t2 {
    int a[8];
  } __attribute__((aligned(64))) __attribute__((preserve_access_index));
  struct t1 {
    int f1:1;
    int f2:2;
    struct t2 f3;
  } __attribute__((preserve_access_index));

Note that struct t2 has aligned 64, which is used sometimes in the
kernel to enforce cache line alignment.

The above struct will be encoded into BTF and the following is what
C code looks like and the struct will appear in the file like vmlinux.h.
  struct t2 {
        int a[8];
        long: 64;
        long: 64;
        long: 64;
        long: 64;
  } __attribute__((preserve_access_index));
  struct t1 {
        int f1: 1;
        int f2: 2;
        long: 61;
        long: 64;
        long: 64;
        long: 64;
        long: 64;
        long: 64;
        long: 64;
        long: 64;
        struct t2 f3;
  } __attribute__((preserve_access_index));

Note that after
  origin_source -> BTF -> new_source
transition, the new source has the same memory layout as the old one
but the alignment interpretation inside the compiler could be different.
The bpf program will use the later explicitly padded structure as in
vmlinux.h.

In the above case, the compiler internal ABI alignment for new struct t1
is 16 while it is 4 for old struct t1. I didn't do a thorough investigation
why the ABI alignment is 16 and I suspect it is related to anonymous padding
in the above.

Current BPF bitfield CO-RE handling requires alignment <= 8 so proper
bitfield operatin can be performed. Therefore, alignment 16 will cause
a compiler fatal error.

To fix the ABI alignment >=16, let us check whether the bitfield
can be held within a 8-byte-aligned range. If this is the case,
we can use alignment 8. Otherwise, a fatal error will be reported.

Differential Revision: https://reviews.llvm.org/D121821
2022-03-16 12:16:46 -07:00

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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/BinaryFormat/Dwarf.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicsBPF.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.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;
uint32_t BPFCoreSharedInfo::SeqNum;
Instruction *BPFCoreSharedInfo::insertPassThrough(Module *M, BasicBlock *BB,
Instruction *Input,
Instruction *Before) {
Function *Fn = Intrinsic::getDeclaration(
M, Intrinsic::bpf_passthrough, {Input->getType(), Input->getType()});
Constant *SeqNumVal = ConstantInt::get(Type::getInt32Ty(BB->getContext()),
BPFCoreSharedInfo::SeqNum++);
auto *NewInst = CallInst::Create(Fn, {SeqNumVal, Input});
BB->getInstList().insert(Before->getIterator(), NewInst);
return NewInst;
}
} // namespace llvm
using namespace llvm;
namespace {
class BPFAbstractMemberAccess final {
public:
BPFAbstractMemberAccess(BPFTargetMachine *TM) : TM(TM) {}
bool run(Function &F);
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,
};
TargetMachine *TM;
const DataLayout *DL = nullptr;
Module *M = nullptr;
static 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(Function &F);
void traceAICall(CallInst *Call, CallInfo &ParentInfo);
void traceBitCast(BitCastInst *BitCast, CallInst *Parent,
CallInfo &ParentInfo);
void traceGEP(GetElementPtrInst *GEP, CallInst *Parent,
CallInfo &ParentInfo);
void collectAICallChains(Function &F);
bool IsPreserveDIAccessIndexCall(const CallInst *Call, CallInfo &Cinfo);
bool IsValidAIChain(const MDNode *ParentMeta, uint32_t ParentAI,
const MDNode *ChildMeta);
bool removePreserveAccessIndexIntrinsic(Function &F);
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);
MDNode *computeAccessKey(CallInst *Call, CallInfo &CInfo,
std::string &AccessKey, bool &IsInt32Ret);
uint64_t getConstant(const Value *IndexValue);
bool transformGEPChain(CallInst *Call, CallInfo &CInfo);
};
std::map<std::string, GlobalVariable *> BPFAbstractMemberAccess::GEPGlobals;
class BPFAbstractMemberAccessLegacyPass final : public FunctionPass {
BPFTargetMachine *TM;
bool runOnFunction(Function &F) override {
return BPFAbstractMemberAccess(TM).run(F);
}
public:
static char ID;
// 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.
BPFAbstractMemberAccessLegacyPass(BPFTargetMachine *TM = nullptr)
: FunctionPass(ID), TM(TM) {}
};
} // End anonymous namespace
char BPFAbstractMemberAccessLegacyPass::ID = 0;
INITIALIZE_PASS(BPFAbstractMemberAccessLegacyPass, DEBUG_TYPE,
"BPF Abstract Member Access", false, false)
FunctionPass *llvm::createBPFAbstractMemberAccess(BPFTargetMachine *TM) {
return new BPFAbstractMemberAccessLegacyPass(TM);
}
bool BPFAbstractMemberAccess::run(Function &F) {
LLVM_DEBUG(dbgs() << "********** Abstract Member Accesses **********\n");
M = F.getParent();
if (!M)
return false;
// Bail out if no debug info.
if (M->debug_compile_units().empty())
return false;
DL = &M->getDataLayout();
return doTransformation(F);
}
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;
}
static Type *getBaseElementType(const CallInst *Call) {
// Element type is stored in an elementtype() attribute on the first param.
return Call->getParamElementType(0);
}
/// 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(getBaseElementType(Call));
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(getBaseElementType(Call));
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;
}
if (GV->getName().startswith("llvm.bpf.preserve.type.info")) {
CInfo.Kind = BPFPreserveFieldInfoAI;
CInfo.Metadata = Call->getMetadata(LLVMContext::MD_preserve_access_index);
if (!CInfo.Metadata)
report_fatal_error("Missing metadata for llvm.preserve.type.info intrinsic");
uint64_t Flag = getConstant(Call->getArgOperand(1));
if (Flag >= BPFCoreSharedInfo::MAX_PRESERVE_TYPE_INFO_FLAG)
report_fatal_error("Incorrect flag for llvm.bpf.preserve.type.info intrinsic");
if (Flag == BPFCoreSharedInfo::PRESERVE_TYPE_INFO_EXISTENCE)
CInfo.AccessIndex = BPFCoreSharedInfo::TYPE_EXISTENCE;
else
CInfo.AccessIndex = BPFCoreSharedInfo::TYPE_SIZE;
return true;
}
if (GV->getName().startswith("llvm.bpf.preserve.enum.value")) {
CInfo.Kind = BPFPreserveFieldInfoAI;
CInfo.Metadata = Call->getMetadata(LLVMContext::MD_preserve_access_index);
if (!CInfo.Metadata)
report_fatal_error("Missing metadata for llvm.preserve.enum.value intrinsic");
uint64_t Flag = getConstant(Call->getArgOperand(2));
if (Flag >= BPFCoreSharedInfo::MAX_PRESERVE_ENUM_VALUE_FLAG)
report_fatal_error("Incorrect flag for llvm.bpf.preserve.enum.value intrinsic");
if (Flag == BPFCoreSharedInfo::PRESERVE_ENUM_VALUE_EXISTENCE)
CInfo.AccessIndex = BPFCoreSharedInfo::ENUM_VALUE_EXISTENCE;
else
CInfo.AccessIndex = BPFCoreSharedInfo::ENUM_VALUE;
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(
getBaseElementType(Call), Call->getArgOperand(0), IdxList, "", Call);
Call->replaceAllUsesWith(GEP);
Call->eraseFromParent();
}
}
bool BPFAbstractMemberAccess::removePreserveAccessIndexIntrinsic(Function &F) {
std::vector<CallInst *> PreserveArrayIndexCalls;
std::vector<CallInst *> PreserveUnionIndexCalls;
std::vector<CallInst *> PreserveStructIndexCalls;
bool Found = false;
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(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();
if (RecordAlignment > 8) {
// If the Bits are within an aligned 8-byte, set the RecordAlignment
// to 8, other report the fatal error.
if (MemberBitOffset / 64 != (MemberBitOffset + MemberBitSize) / 64)
report_fatal_error("Unsupported field expression for llvm.bpf.preserve.field.info, "
"requiring too big alignment");
RecordAlignment = Align(8);
}
uint32_t AlignBits = RecordAlignment.value() * 8;
if (MemberBitSize > AlignBits)
report_fatal_error("Unsupported field expression for llvm.bpf.preserve.field.info, "
"bitfield size greater than record 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;
if (InfoKind == BPFCoreSharedInfo::FIELD_EXISTENCE)
PatchImm = 1;
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;
}
MDNode *BPFAbstractMemberAccess::computeAccessKey(CallInst *Call,
CallInfo &CInfo,
std::string &AccessKey,
bool &IsInt32Ret) {
DIType *Ty = stripQualifiers(cast<DIType>(CInfo.Metadata), false);
assert(!Ty->getName().empty());
int64_t PatchImm;
std::string AccessStr("0");
if (CInfo.AccessIndex == BPFCoreSharedInfo::TYPE_EXISTENCE) {
PatchImm = 1;
} else if (CInfo.AccessIndex == BPFCoreSharedInfo::TYPE_SIZE) {
// typedef debuginfo type has size 0, get the eventual base type.
DIType *BaseTy = stripQualifiers(Ty, true);
PatchImm = BaseTy->getSizeInBits() / 8;
} else {
// ENUM_VALUE_EXISTENCE and ENUM_VALUE
IsInt32Ret = false;
const auto *CE = cast<ConstantExpr>(Call->getArgOperand(1));
const GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
assert(GV->hasInitializer());
const ConstantDataArray *DA = cast<ConstantDataArray>(GV->getInitializer());
assert(DA->isString());
StringRef ValueStr = DA->getAsString();
// ValueStr format: <EnumeratorStr>:<Value>
size_t Separator = ValueStr.find_first_of(':');
StringRef EnumeratorStr = ValueStr.substr(0, Separator);
// Find enumerator index in the debuginfo
DIType *BaseTy = stripQualifiers(Ty, true);
const auto *CTy = cast<DICompositeType>(BaseTy);
assert(CTy->getTag() == dwarf::DW_TAG_enumeration_type);
int EnumIndex = 0;
for (const auto Element : CTy->getElements()) {
const auto *Enum = cast<DIEnumerator>(Element);
if (Enum->getName() == EnumeratorStr) {
AccessStr = std::to_string(EnumIndex);
break;
}
EnumIndex++;
}
if (CInfo.AccessIndex == BPFCoreSharedInfo::ENUM_VALUE) {
StringRef EValueStr = ValueStr.substr(Separator + 1);
PatchImm = std::stoll(std::string(EValueStr));
} else {
PatchImm = 1;
}
}
AccessKey = "llvm." + Ty->getName().str() + ":" +
std::to_string(CInfo.AccessIndex) + std::string(":") +
std::to_string(PatchImm) + std::string("$") + AccessStr;
return Ty;
}
/// Call/Kind is the base preserve_*_access_index() call. Attempts to do
/// transformation to a chain of relocable GEPs.
bool BPFAbstractMemberAccess::transformGEPChain(CallInst *Call,
CallInfo &CInfo) {
std::string AccessKey;
MDNode *TypeMeta;
Value *Base = nullptr;
bool IsInt32Ret;
IsInt32Ret = CInfo.Kind == BPFPreserveFieldInfoAI;
if (CInfo.Kind == BPFPreserveFieldInfoAI && CInfo.Metadata) {
TypeMeta = computeAccessKey(Call, CInfo, AccessKey, IsInt32Ret);
} else {
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 (IsInt32Ret)
VarType = Type::getInt32Ty(BB->getContext()); // 32bit return value
else
VarType = Type::getInt64Ty(BB->getContext()); // 64bit ptr or enum value
GV = new GlobalVariable(*M, VarType, false, GlobalVariable::ExternalLinkage,
nullptr, 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.
LoadInst *LDInst;
if (IsInt32Ret)
LDInst = new LoadInst(Type::getInt32Ty(BB->getContext()), GV, "", Call);
else
LDInst = new LoadInst(Type::getInt64Ty(BB->getContext()), GV, "", Call);
Instruction *PassThroughInst =
BPFCoreSharedInfo::insertPassThrough(M, BB, LDInst, Call);
Call->replaceAllUsesWith(PassThroughInst);
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 llvm.sk_buff:0:50$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);
// For the following code,
// Block0:
// ...
// if (...) goto Block1 else ...
// Block1:
// %6 = load llvm.sk_buff:0:50$0:0:0:2:0
// %7 = bitcast %struct.sk_buff* %2 to i8*
// %8 = getelementptr i8, i8* %7, %6
// ...
// goto CommonExit
// Block2:
// ...
// if (...) goto Block3 else ...
// Block3:
// %6 = load llvm.bpf_map:0:40$0:0:0:2:0
// %7 = bitcast %struct.sk_buff* %2 to i8*
// %8 = getelementptr i8, i8* %7, %6
// ...
// goto CommonExit
// CommonExit
// SimplifyCFG may generate:
// Block0:
// ...
// if (...) goto Block_Common else ...
// Block2:
// ...
// if (...) goto Block_Common else ...
// Block_Common:
// PHI = [llvm.sk_buff:0:50$0:0:0:2:0, llvm.bpf_map:0:40$0:0:0:2:0]
// %6 = load PHI
// %7 = bitcast %struct.sk_buff* %2 to i8*
// %8 = getelementptr i8, i8* %7, %6
// ...
// goto CommonExit
// For the above code, we cannot perform proper relocation since
// "load PHI" has two possible relocations.
//
// To prevent above tail merging, we use __builtin_bpf_passthrough()
// where one of its parameters is a seq_num. Since two
// __builtin_bpf_passthrough() funcs will always have different seq_num,
// tail merging cannot happen. The __builtin_bpf_passthrough() will be
// removed in the beginning of Target IR passes.
//
// This approach is also used in other places when global var
// representing a relocation is used.
Instruction *PassThroughInst =
BPFCoreSharedInfo::insertPassThrough(M, BB, BCInst2, Call);
Call->replaceAllUsesWith(PassThroughInst);
Call->eraseFromParent();
return true;
}
bool BPFAbstractMemberAccess::doTransformation(Function &F) {
bool Transformed = false;
// Collect PreserveDIAccessIndex Intrinsic call chains.
// The call chains will be used to generate the access
// patterns similar to GEP.
collectAICallChains(F);
for (auto &C : BaseAICalls)
Transformed = transformGEPChain(C.first, C.second) || Transformed;
return removePreserveAccessIndexIntrinsic(F) || Transformed;
}
PreservedAnalyses
BPFAbstractMemberAccessPass::run(Function &F, FunctionAnalysisManager &AM) {
return BPFAbstractMemberAccess(TM).run(F) ? PreservedAnalyses::none()
: PreservedAnalyses::all();
}
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