1 //===----------- BPFPreserveDIType.cpp - Preserve DebugInfo Types ---------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // Preserve Debuginfo types encoded in __builtin_btf_type_id() metadata.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "BPF.h"
14 #include "BPFCORE.h"
15 #include "llvm/BinaryFormat/Dwarf.h"
16 #include "llvm/IR/DebugInfoMetadata.h"
17 #include "llvm/IR/GlobalVariable.h"
18 #include "llvm/IR/Instruction.h"
19 #include "llvm/IR/Instructions.h"
20 #include "llvm/IR/Module.h"
21 #include "llvm/IR/PassManager.h"
22 #include "llvm/IR/Type.h"
23 #include "llvm/IR/User.h"
24 #include "llvm/IR/Value.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
27
28 #define DEBUG_TYPE "bpf-preserve-di-type"
29
30 namespace llvm {
31 constexpr StringRef BPFCoreSharedInfo::TypeIdAttr;
32 } // namespace llvm
33
34 using namespace llvm;
35
36 namespace {
37
BPFPreserveDITypeImpl(Function & F)38 static bool BPFPreserveDITypeImpl(Function &F) {
39 LLVM_DEBUG(dbgs() << "********** preserve debuginfo type **********\n");
40
41 Module *M = F.getParent();
42
43 // Bail out if no debug info.
44 if (M->debug_compile_units().empty())
45 return false;
46
47 std::vector<CallInst *> PreserveDITypeCalls;
48
49 for (auto &BB : F) {
50 for (auto &I : BB) {
51 auto *Call = dyn_cast<CallInst>(&I);
52 if (!Call)
53 continue;
54
55 const auto *GV = dyn_cast<GlobalValue>(Call->getCalledOperand());
56 if (!GV)
57 continue;
58
59 if (GV->getName().startswith("llvm.bpf.btf.type.id")) {
60 if (!Call->getMetadata(LLVMContext::MD_preserve_access_index))
61 report_fatal_error(
62 "Missing metadata for llvm.bpf.btf.type.id intrinsic");
63 PreserveDITypeCalls.push_back(Call);
64 }
65 }
66 }
67
68 if (PreserveDITypeCalls.empty())
69 return false;
70
71 std::string BaseName = "llvm.btf_type_id.";
72 static int Count = 0;
73 for (auto *Call : PreserveDITypeCalls) {
74 const ConstantInt *Flag = dyn_cast<ConstantInt>(Call->getArgOperand(1));
75 assert(Flag);
76 uint64_t FlagValue = Flag->getValue().getZExtValue();
77
78 if (FlagValue >= BPFCoreSharedInfo::MAX_BTF_TYPE_ID_FLAG)
79 report_fatal_error("Incorrect flag for llvm.bpf.btf.type.id intrinsic");
80
81 MDNode *MD = Call->getMetadata(LLVMContext::MD_preserve_access_index);
82
83 uint32_t Reloc;
84 if (FlagValue == BPFCoreSharedInfo::BTF_TYPE_ID_LOCAL_RELOC) {
85 Reloc = BPFCoreSharedInfo::BTF_TYPE_ID_LOCAL;
86 } else {
87 Reloc = BPFCoreSharedInfo::BTF_TYPE_ID_REMOTE;
88 DIType *Ty = cast<DIType>(MD);
89 while (auto *DTy = dyn_cast<DIDerivedType>(Ty)) {
90 unsigned Tag = DTy->getTag();
91 if (Tag != dwarf::DW_TAG_const_type &&
92 Tag != dwarf::DW_TAG_volatile_type)
93 break;
94 Ty = DTy->getBaseType();
95 }
96
97 if (Ty->getName().empty()) {
98 if (isa<DISubroutineType>(Ty))
99 report_fatal_error(
100 "SubroutineType not supported for BTF_TYPE_ID_REMOTE reloc");
101 else
102 report_fatal_error("Empty type name for BTF_TYPE_ID_REMOTE reloc");
103 }
104 MD = Ty;
105 }
106
107 BasicBlock *BB = Call->getParent();
108 IntegerType *VarType = Type::getInt64Ty(BB->getContext());
109 std::string GVName =
110 BaseName + std::to_string(Count) + "$" + std::to_string(Reloc);
111 GlobalVariable *GV = new GlobalVariable(
112 *M, VarType, false, GlobalVariable::ExternalLinkage, nullptr, GVName);
113 GV->addAttribute(BPFCoreSharedInfo::TypeIdAttr);
114 GV->setMetadata(LLVMContext::MD_preserve_access_index, MD);
115
116 // Load the global variable which represents the type info.
117 auto *LDInst =
118 new LoadInst(Type::getInt64Ty(BB->getContext()), GV, "", Call);
119 Instruction *PassThroughInst =
120 BPFCoreSharedInfo::insertPassThrough(M, BB, LDInst, Call);
121 Call->replaceAllUsesWith(PassThroughInst);
122 Call->eraseFromParent();
123 Count++;
124 }
125
126 return true;
127 }
128
129 class BPFPreserveDIType final : public FunctionPass {
130 bool runOnFunction(Function &F) override;
131
132 public:
133 static char ID;
BPFPreserveDIType()134 BPFPreserveDIType() : FunctionPass(ID) {}
135 };
136 } // End anonymous namespace
137
138 char BPFPreserveDIType::ID = 0;
139 INITIALIZE_PASS(BPFPreserveDIType, DEBUG_TYPE, "BPF Preserve Debuginfo Type",
140 false, false)
141
createBPFPreserveDIType()142 FunctionPass *llvm::createBPFPreserveDIType() {
143 return new BPFPreserveDIType();
144 }
145
runOnFunction(Function & F)146 bool BPFPreserveDIType::runOnFunction(Function &F) {
147 return BPFPreserveDITypeImpl(F);
148 }
149
run(Function & F,FunctionAnalysisManager & AM)150 PreservedAnalyses BPFPreserveDITypePass::run(Function &F,
151 FunctionAnalysisManager &AM) {
152 return BPFPreserveDITypeImpl(F) ? PreservedAnalyses::none()
153 : PreservedAnalyses::all();
154 }
155