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/DebugInfo/BTF/BTF.h"
17#include "llvm/IR/DebugInfoMetadata.h"
18#include "llvm/IR/GlobalVariable.h"
19#include "llvm/IR/Instruction.h"
20#include "llvm/IR/Instructions.h"
21#include "llvm/IR/Module.h"
22#include "llvm/IR/PassManager.h"
23#include "llvm/IR/Type.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
30namespace llvm {
31constexpr StringRef BPFCoreSharedInfo::TypeIdAttr;
32} // namespace llvm
33
34using namespace llvm;
35
36namespace {
37
38static 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>(Val: &I);
52 if (!Call)
53 continue;
54
55 const auto *GV = dyn_cast<GlobalValue>(Val: Call->getCalledOperand());
56 if (!GV)
57 continue;
58
59 if (GV->getName().starts_with(Prefix: "llvm.bpf.btf.type.id")) {
60 if (!Call->getMetadata(KindID: LLVMContext::MD_preserve_access_index))
61 report_fatal_error(
62 reason: "Missing metadata for llvm.bpf.btf.type.id intrinsic");
63 PreserveDITypeCalls.push_back(x: 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>(Val: Call->getArgOperand(i: 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(reason: "Incorrect flag for llvm.bpf.btf.type.id intrinsic");
80
81 MDNode *MD = Call->getMetadata(KindID: LLVMContext::MD_preserve_access_index);
82
83 uint32_t Reloc;
84 if (FlagValue == BPFCoreSharedInfo::BTF_TYPE_ID_LOCAL_RELOC) {
85 Reloc = BTF::BTF_TYPE_ID_LOCAL;
86 } else {
87 Reloc = BTF::BTF_TYPE_ID_REMOTE;
88 }
89 DIType *Ty = cast<DIType>(Val: MD);
90 while (auto *DTy = dyn_cast<DIDerivedType>(Val: Ty)) {
91 unsigned Tag = DTy->getTag();
92 if (Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type)
93 break;
94 Ty = DTy->getBaseType();
95 }
96
97 if (Reloc == BTF::BTF_TYPE_ID_REMOTE) {
98 if (Ty->getName().empty()) {
99 if (isa<DISubroutineType>(Val: Ty))
100 report_fatal_error(
101 reason: "SubroutineType not supported for BTF_TYPE_ID_REMOTE reloc");
102 else
103 report_fatal_error(reason: "Empty type name for BTF_TYPE_ID_REMOTE reloc");
104 }
105 }
106 MD = Ty;
107
108 BasicBlock *BB = Call->getParent();
109 IntegerType *VarType = Type::getInt64Ty(C&: BB->getContext());
110 std::string GVName =
111 BaseName + std::to_string(val: Count) + "$" + std::to_string(val: Reloc);
112 GlobalVariable *GV = new GlobalVariable(
113 *M, VarType, false, GlobalVariable::ExternalLinkage, nullptr, GVName);
114 GV->addAttribute(Kind: BPFCoreSharedInfo::TypeIdAttr);
115 GV->setMetadata(KindID: LLVMContext::MD_preserve_access_index, Node: MD);
116
117 // Load the global variable which represents the type info.
118 auto *LDInst = new LoadInst(Type::getInt64Ty(C&: BB->getContext()), GV, "",
119 Call->getIterator());
120 Instruction *PassThroughInst =
121 BPFCoreSharedInfo::insertPassThrough(M, BB, Input: LDInst, Before: Call);
122 Call->replaceAllUsesWith(V: PassThroughInst);
123 Call->eraseFromParent();
124 Count++;
125 }
126
127 return true;
128}
129} // End anonymous namespace
130
131PreservedAnalyses BPFPreserveDITypePass::run(Function &F,
132 FunctionAnalysisManager &AM) {
133 return BPFPreserveDITypeImpl(F) ? PreservedAnalyses::none()
134 : PreservedAnalyses::all();
135}
136