llvm/lib/Target/BPF/BPFPreserveDIType.cpp

   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/User.h"
  25 #include "llvm/IR/Value.h"
  26 #include "llvm/Pass.h"
  27 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  28
  29 #define DEBUG_TYPE "bpf-preserve-di-type"
  30
  31 namespace llvm {
  32 constexpr StringRef BPFCoreSharedInfo::TypeIdAttr;
  33 } // namespace llvm
  34
  35 using namespace llvm;
  36
  37 namespace {
  38
  39 static bool BPFPreserveDITypeImpl(Function &F) {
  40   LLVM_DEBUG(dbgs() << "********** preserve debuginfo type **********\n");
  41
  42   Module *M = F.getParent();
  43
  44   // Bail out if no debug info.
  45   if (M->debug_compile_units().empty())
  46     return false;
  47
  48   std::vector<CallInst *> PreserveDITypeCalls;
  49
  50   for (auto &BB : F) {
  51     for (auto &I : BB) {
  52       auto *Call = dyn_cast<CallInst>(&I);
  53       if (!Call)
  54         continue;
  55
  56       const auto *GV = dyn_cast<GlobalValue>(Call->getCalledOperand());
  57       if (!GV)
  58         continue;
  59
  60       if (GV->getName().starts_with("llvm.bpf.btf.type.id")) {
  61         if (!Call->getMetadata(LLVMContext::MD_preserve_access_index))
  62           report_fatal_error(
  63               "Missing metadata for llvm.bpf.btf.type.id intrinsic");
  64         PreserveDITypeCalls.push_back(Call);
  65       }
  66     }
  67   }
  68
  69   if (PreserveDITypeCalls.empty())
  70     return false;
  71
  72   std::string BaseName = "llvm.btf_type_id.";
  73   static int Count = 0;
  74   for (auto *Call : PreserveDITypeCalls) {
  75     const ConstantInt *Flag = dyn_cast<ConstantInt>(Call->getArgOperand(1));
  76     assert(Flag);
  77     uint64_t FlagValue = Flag->getValue().getZExtValue();
  78
  79     if (FlagValue >= BPFCoreSharedInfo::MAX_BTF_TYPE_ID_FLAG)
  80       report_fatal_error("Incorrect flag for llvm.bpf.btf.type.id intrinsic");
  81
  82     MDNode *MD = Call->getMetadata(LLVMContext::MD_preserve_access_index);
  83
  84     uint32_t Reloc;
  85     if (FlagValue == BPFCoreSharedInfo::BTF_TYPE_ID_LOCAL_RELOC) {
  86       Reloc = BTF::BTF_TYPE_ID_LOCAL;
  87     } else {
  88       Reloc = BTF::BTF_TYPE_ID_REMOTE;
  89     }
  90     DIType *Ty = cast<DIType>(MD);
  91     while (auto *DTy = dyn_cast<DIDerivedType>(Ty)) {
  92       unsigned Tag = DTy->getTag();
  93       if (Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type)
  94         break;
  95       Ty = DTy->getBaseType();
  96     }
  97
  98     if (Reloc == BTF::BTF_TYPE_ID_REMOTE) {
  99       if (Ty->getName().empty()) {
 100         if (isa<DISubroutineType>(Ty))
 101           report_fatal_error(
 102               "SubroutineType not supported for BTF_TYPE_ID_REMOTE reloc");
 103         else
 104           report_fatal_error("Empty type name for BTF_TYPE_ID_REMOTE reloc");
 105       }
 106     }
 107     MD = Ty;
 108
 109     BasicBlock *BB = Call->getParent();
 110     IntegerType *VarType = Type::getInt64Ty(BB->getContext());
 111     std::string GVName =
 112         BaseName + std::to_string(Count) + "$" + std::to_string(Reloc);
 113     GlobalVariable *GV = new GlobalVariable(
 114         *M, VarType, false, GlobalVariable::ExternalLinkage, nullptr, GVName);
 115     GV->addAttribute(BPFCoreSharedInfo::TypeIdAttr);
 116     GV->setMetadata(LLVMContext::MD_preserve_access_index, MD);
 117
 118     // Load the global variable which represents the type info.
 119     auto *LDInst =
 120         new LoadInst(Type::getInt64Ty(BB->getContext()), GV, "", Call);
 121     Instruction *PassThroughInst =
 122         BPFCoreSharedInfo::insertPassThrough(M, BB, LDInst, Call);
 123     Call->replaceAllUsesWith(PassThroughInst);
 124     Call->eraseFromParent();
 125     Count++;
 126   }
 127
 128   return true;
 129 }
 130 } // End anonymous namespace
 131
 132 PreservedAnalyses BPFPreserveDITypePass::run(Function &F,
 133                                              FunctionAnalysisManager &AM) {
 134   return BPFPreserveDITypeImpl(F) ? PreservedAnalyses::none()
 135                                   : PreservedAnalyses::all();
 136 }