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