1 //===---- IndirectThunks.h - Indirect Thunk Base Class ----------*- C++ -*-===//
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 /// \file
10 /// Contains a base class for Passes that inject an MI thunk.
11 ///
12 //===----------------------------------------------------------------------===//
13
14 #ifndef LLVM_CODEGEN_INDIRECTTHUNKS_H
15 #define LLVM_CODEGEN_INDIRECTTHUNKS_H
16
17 #include "llvm/CodeGen/MachineFunction.h"
18 #include "llvm/CodeGen/MachineModuleInfo.h"
19 #include "llvm/IR/IRBuilder.h"
20 #include "llvm/IR/Module.h"
21
22 namespace llvm {
23
24 template <typename Derived> class ThunkInserter {
getDerived()25 Derived &getDerived() { return *static_cast<Derived *>(this); }
26
27 protected:
28 bool InsertedThunks;
doInitialization(Module & M)29 void doInitialization(Module &M) {}
30 void createThunkFunction(MachineModuleInfo &MMI, StringRef Name,
31 bool Comdat = true);
32
33 public:
init(Module & M)34 void init(Module &M) {
35 InsertedThunks = false;
36 getDerived().doInitialization(M);
37 }
38 // return `true` if `MMI` or `MF` was modified
39 bool run(MachineModuleInfo &MMI, MachineFunction &MF);
40 };
41
42 template <typename Derived>
createThunkFunction(MachineModuleInfo & MMI,StringRef Name,bool Comdat)43 void ThunkInserter<Derived>::createThunkFunction(MachineModuleInfo &MMI,
44 StringRef Name, bool Comdat) {
45 assert(Name.startswith(getDerived().getThunkPrefix()) &&
46 "Created a thunk with an unexpected prefix!");
47
48 Module &M = const_cast<Module &>(*MMI.getModule());
49 LLVMContext &Ctx = M.getContext();
50 auto Type = FunctionType::get(Type::getVoidTy(Ctx), false);
51 Function *F = Function::Create(Type,
52 Comdat ? GlobalValue::LinkOnceODRLinkage
53 : GlobalValue::InternalLinkage,
54 Name, &M);
55 if (Comdat) {
56 F->setVisibility(GlobalValue::HiddenVisibility);
57 F->setComdat(M.getOrInsertComdat(Name));
58 }
59
60 // Add Attributes so that we don't create a frame, unwind information, or
61 // inline.
62 AttrBuilder B;
63 B.addAttribute(llvm::Attribute::NoUnwind);
64 B.addAttribute(llvm::Attribute::Naked);
65 F->addAttributes(llvm::AttributeList::FunctionIndex, B);
66
67 // Populate our function a bit so that we can verify.
68 BasicBlock *Entry = BasicBlock::Create(Ctx, "entry", F);
69 IRBuilder<> Builder(Entry);
70
71 Builder.CreateRetVoid();
72
73 // MachineFunctions aren't created automatically for the IR-level constructs
74 // we already made. Create them and insert them into the module.
75 MachineFunction &MF = MMI.getOrCreateMachineFunction(*F);
76 // A MachineBasicBlock must not be created for the Entry block; code
77 // generation from an empty naked function in C source code also does not
78 // generate one. At least GlobalISel asserts if this invariant isn't
79 // respected.
80
81 // Set MF properties. We never use vregs...
82 MF.getProperties().set(MachineFunctionProperties::Property::NoVRegs);
83 }
84
85 template <typename Derived>
run(MachineModuleInfo & MMI,MachineFunction & MF)86 bool ThunkInserter<Derived>::run(MachineModuleInfo &MMI, MachineFunction &MF) {
87 // If MF is not a thunk, check to see if we need to insert a thunk.
88 if (!MF.getName().startswith(getDerived().getThunkPrefix())) {
89 // If we've already inserted a thunk, nothing else to do.
90 if (InsertedThunks)
91 return false;
92
93 // Only add a thunk if one of the functions has the corresponding feature
94 // enabled in its subtarget, and doesn't enable external thunks.
95 // FIXME: Conditionalize on indirect calls so we don't emit a thunk when
96 // nothing will end up calling it.
97 // FIXME: It's a little silly to look at every function just to enumerate
98 // the subtargets, but eventually we'll want to look at them for indirect
99 // calls, so maybe this is OK.
100 if (!getDerived().mayUseThunk(MF))
101 return false;
102
103 getDerived().insertThunks(MMI);
104 InsertedThunks = true;
105 return true;
106 }
107
108 // If this *is* a thunk function, we need to populate it with the correct MI.
109 getDerived().populateThunk(MF);
110 return true;
111 }
112
113 } // namespace llvm
114
115 #endif
116