1 //===-- WebAssemblyAddMissingPrototypes.cpp - Fix prototypeless functions -===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 ///
10 /// \file
11 /// Add prototypes to prototypes-less functions.
12 ///
13 /// WebAssembly has strict function prototype checking so we need functions
14 /// declarations to match the call sites. Clang treats prototype-less functions
15 /// as varargs (foo(...)) which happens to work on existing platforms but
16 /// doesn't under WebAssembly. This pass will find all the call sites of each
17 /// prototype-less function, ensure they agree, and then set the signature
18 /// on the function declaration accordingly.
19 ///
20 //===----------------------------------------------------------------------===//
21
22 #include "WebAssembly.h"
23 #include "llvm/IR/Constants.h"
24 #include "llvm/IR/IRBuilder.h"
25 #include "llvm/IR/Module.h"
26 #include "llvm/IR/Operator.h"
27 #include "llvm/Transforms/Utils/ModuleUtils.h"
28 #include "llvm/Transforms/Utils/Local.h"
29 #include "llvm/Pass.h"
30 #include "llvm/Support/Debug.h"
31 using namespace llvm;
32
33 #define DEBUG_TYPE "wasm-add-missing-prototypes"
34
35 namespace {
36 class WebAssemblyAddMissingPrototypes final : public ModulePass {
getPassName() const37 StringRef getPassName() const override {
38 return "Add prototypes to prototypes-less functions";
39 }
40
getAnalysisUsage(AnalysisUsage & AU) const41 void getAnalysisUsage(AnalysisUsage &AU) const override {
42 AU.setPreservesCFG();
43 ModulePass::getAnalysisUsage(AU);
44 }
45
46 bool runOnModule(Module &M) override;
47
48 public:
49 static char ID;
WebAssemblyAddMissingPrototypes()50 WebAssemblyAddMissingPrototypes() : ModulePass(ID) {}
51 };
52 } // End anonymous namespace
53
54 char WebAssemblyAddMissingPrototypes::ID = 0;
55 INITIALIZE_PASS(WebAssemblyAddMissingPrototypes, DEBUG_TYPE,
56 "Add prototypes to prototypes-less functions", false, false)
57
createWebAssemblyAddMissingPrototypes()58 ModulePass *llvm::createWebAssemblyAddMissingPrototypes() {
59 return new WebAssemblyAddMissingPrototypes();
60 }
61
runOnModule(Module & M)62 bool WebAssemblyAddMissingPrototypes::runOnModule(Module &M) {
63 LLVM_DEBUG(dbgs() << "runnning AddMissingPrototypes\n");
64
65 std::vector<std::pair<Function*, Function*>> Replacements;
66
67 // Find all the prototype-less function declarations
68 for (Function &F : M) {
69 if (!F.isDeclaration() || !F.hasFnAttribute("no-prototype"))
70 continue;
71
72 LLVM_DEBUG(dbgs() << "Found no-prototype function: " << F.getName() << "\n");
73
74 // When clang emits prototype-less C functions it uses (...), i.e. varargs
75 // function that take no arguments (have no sentinel). When we see a
76 // no-prototype attribute we expect the function have these properties.
77 if (!F.isVarArg())
78 report_fatal_error(
79 "Functions with 'no-prototype' attribute must take varargs: " +
80 F.getName());
81 if (F.getFunctionType()->getNumParams() != 0)
82 report_fatal_error(
83 "Functions with 'no-prototype' attribute should not have params: " +
84 F.getName());
85
86
87 // Create a function prototype based on the first call site (first bitcast)
88 // that we find.
89 FunctionType *NewType = nullptr;
90 Function* NewF = nullptr;
91 for (Use &U : F.uses()) {
92 LLVM_DEBUG(dbgs() << "prototype-less use: " << F.getName() << "\n");
93 if (BitCastOperator *BC = dyn_cast<BitCastOperator>(U.getUser())) {
94 FunctionType *DestType =
95 cast<FunctionType>(BC->getDestTy()->getPointerElementType());
96
97 // Create a new function with the correct type
98 NewType = DestType;
99 NewF = Function::Create(NewType, F.getLinkage(), F.getName());
100 NewF->setAttributes(F.getAttributes());
101 NewF->removeFnAttr("no-prototype");
102 break;
103 }
104 }
105
106 if (!NewType) {
107 LLVM_DEBUG(
108 dbgs() << "could not derive a function prototype from usage: " +
109 F.getName() + "\n");
110 continue;
111 }
112
113 for (Use &U : F.uses()) {
114 if (BitCastOperator *BC = dyn_cast<BitCastOperator>(U.getUser())) {
115 FunctionType *DestType =
116 cast<FunctionType>(BC->getDestTy()->getPointerElementType());
117 if (NewType != DestType) {
118 report_fatal_error(
119 "Prototypeless function used with conflicting signatures: " +
120 F.getName());
121 }
122 BC->replaceAllUsesWith(NewF);
123 Replacements.emplace_back(&F, NewF);
124 } else {
125 dbgs() << *U.getUser()->getType() << "\n";
126 #ifndef NDEBUG
127 U.getUser()->dump();
128 #endif
129 report_fatal_error(
130 "unexpected use of prototypeless function: " + F.getName() + "\n");
131 }
132 }
133 }
134
135 // Finally replace the old function declarations with the new ones
136 for (auto &Pair : Replacements) {
137 Function* Old = Pair.first;
138 Function* New = Pair.second;
139 Old->eraseFromParent();
140 M.getFunctionList().push_back(New);
141 }
142
143 return !Replacements.empty();
144 }
145