1 //===- bolt/Passes/PatchEntries.cpp - Pass for patching function entries --===//
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 // This file implements the PatchEntries class that is used for patching
10 // the original function entry points.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "bolt/Passes/PatchEntries.h"
15 #include "bolt/Utils/NameResolver.h"
16 #include "llvm/Support/CommandLine.h"
17 
18 namespace opts {
19 
20 extern llvm::cl::OptionCategory BoltCategory;
21 
22 extern llvm::cl::opt<unsigned> Verbosity;
23 
24 llvm::cl::opt<bool>
25     ForcePatch("force-patch",
26                llvm::cl::desc("force patching of original entry points"),
27                llvm::cl::Hidden, llvm::cl::cat(BoltCategory));
28 }
29 
30 namespace llvm {
31 namespace bolt {
32 
33 void PatchEntries::runOnFunctions(BinaryContext &BC) {
34   if (!opts::ForcePatch) {
35     // Mark the binary for patching if we did not create external references
36     // for original code in any of functions we are not going to emit.
37     bool NeedsPatching = false;
38     for (auto &BFI : BC.getBinaryFunctions()) {
39       BinaryFunction &Function = BFI.second;
40       if (!BC.shouldEmit(Function) && !Function.hasExternalRefRelocations()) {
41         NeedsPatching = true;
42         break;
43       }
44     }
45 
46     if (!NeedsPatching)
47       return;
48   }
49 
50   if (opts::Verbosity >= 1)
51     outs() << "BOLT-INFO: patching entries in original code\n";
52 
53   // Calculate the size of the patch.
54   static size_t PatchSize = 0;
55   if (!PatchSize) {
56     InstructionListType Seq;
57     BC.MIB->createLongTailCall(Seq, BC.Ctx->createTempSymbol(), BC.Ctx.get());
58     PatchSize = BC.computeCodeSize(Seq.begin(), Seq.end());
59   }
60 
61   for (auto &BFI : BC.getBinaryFunctions()) {
62     BinaryFunction &Function = BFI.second;
63 
64     // Patch original code only for functions that will be emitted.
65     if (!BC.shouldEmit(Function))
66       continue;
67 
68     // Check if we can skip patching the function.
69     if (!opts::ForcePatch && !Function.hasEHRanges() &&
70         Function.getSize() < PatchThreshold)
71       continue;
72 
73     // List of patches for function entries. We either successfully patch
74     // all entries or, if we cannot patch one or more, do no patch any and
75     // mark the function as ignorable.
76     std::vector<Patch> PendingPatches;
77 
78     uint64_t NextValidByte = 0; // offset of the byte past the last patch
79     bool Success = Function.forEachEntryPoint([&](uint64_t Offset,
80                                                   const MCSymbol *Symbol) {
81       if (Offset < NextValidByte) {
82         if (opts::Verbosity >= 1)
83           outs() << "BOLT-INFO: unable to patch entry point in " << Function
84                  << " at offset 0x" << Twine::utohexstr(Offset) << '\n';
85         return false;
86       }
87 
88       PendingPatches.emplace_back(Patch{Symbol, Function.getAddress() + Offset,
89                                         Function.getFileOffset() + Offset,
90                                         Function.getOriginSection()});
91       NextValidByte = Offset + PatchSize;
92       if (NextValidByte > Function.getMaxSize()) {
93         if (opts::Verbosity >= 1)
94           outs() << "BOLT-INFO: function " << Function
95                  << " too small to patch its entry point\n";
96         return false;
97       }
98 
99       return true;
100     });
101 
102     if (!Success) {
103       // If the original function entries cannot be patched, then we cannot
104       // safely emit new function body.
105       errs() << "BOLT-WARNING: failed to patch entries in " << Function
106              << ". The function will not be optimized.\n";
107       Function.setIgnored();
108       continue;
109     }
110 
111     for (Patch &Patch : PendingPatches) {
112       BinaryFunction *PatchFunction = BC.createInjectedBinaryFunction(
113           NameResolver::append(Patch.Symbol->getName(), ".org.0"));
114       // Force the function to be emitted at the given address.
115       PatchFunction->setOutputAddress(Patch.Address);
116       PatchFunction->setFileOffset(Patch.FileOffset);
117       PatchFunction->setOriginSection(Patch.Section);
118 
119       InstructionListType Seq;
120       BC.MIB->createLongTailCall(Seq, Patch.Symbol, BC.Ctx.get());
121       PatchFunction->addBasicBlock(0)->addInstructions(Seq);
122 
123       // Verify the size requirements.
124       uint64_t HotSize, ColdSize;
125       std::tie(HotSize, ColdSize) = BC.calculateEmittedSize(*PatchFunction);
126       assert(!ColdSize && "unexpected cold code");
127       assert(HotSize <= PatchSize && "max patch size exceeded");
128     }
129 
130     Function.setIsPatched(true);
131   }
132 }
133 
134 } // end namespace bolt
135 } // end namespace llvm
136