1 //===--------- DefineExternalSectionStartAndEndSymbols.h --------*- 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 // Utility class for recognizing external section start and end symbols and
10 // transforming them into defined symbols for the start and end blocks of the
11 // associated Section.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #ifndef LLVM_EXECUTIONENGINE_JITLINK_DEFINEEXTERNALSECTIONSTARTANDENDSYMBOLS_H
16 #define LLVM_EXECUTIONENGINE_JITLINK_DEFINEEXTERNALSECTIONSTARTANDENDSYMBOLS_H
17
18 #include "llvm/ExecutionEngine/JITLink/JITLink.h"
19 #include "llvm/Support/Debug.h"
20
21 #define DEBUG_TYPE "jitlink"
22
23 namespace llvm {
24 namespace jitlink {
25
26 struct SectionRangeSymbolDesc {
27 SectionRangeSymbolDesc() = default;
SectionRangeSymbolDescSectionRangeSymbolDesc28 SectionRangeSymbolDesc(Section &Sec, bool IsStart)
29 : Sec(&Sec), IsStart(IsStart) {}
30 Section *Sec = nullptr;
31 bool IsStart = false;
32 };
33
34 /// Pass implementation for the createDefineExternalSectionStartAndEndSymbols
35 /// function.
36 template <typename SymbolIdentifierFunction>
37 class DefineExternalSectionStartAndEndSymbols {
38 public:
DefineExternalSectionStartAndEndSymbols(SymbolIdentifierFunction F)39 DefineExternalSectionStartAndEndSymbols(SymbolIdentifierFunction F)
40 : F(std::move(F)) {}
41
operator()42 Error operator()(LinkGraph &G) {
43
44 // This pass will affect the external symbols set, so copy them out into a
45 // vector and iterate over that.
46 std::vector<Symbol *> Externals(G.external_symbols().begin(),
47 G.external_symbols().end());
48
49 for (auto *Sym : Externals) {
50 SectionRangeSymbolDesc D = F(G, *Sym);
51 if (D.Sec) {
52 auto &SR = getSectionRange(*D.Sec);
53 if (D.IsStart) {
54 if (SR.empty())
55 G.makeAbsolute(*Sym, orc::ExecutorAddr());
56 else
57 G.makeDefined(*Sym, *SR.getFirstBlock(), 0, 0, Linkage::Strong,
58 Scope::Local, false);
59 } else {
60 if (SR.empty())
61 G.makeAbsolute(*Sym, orc::ExecutorAddr());
62 else
63 G.makeDefined(*Sym, *SR.getLastBlock(),
64 SR.getLastBlock()->getSize(), 0, Linkage::Strong,
65 Scope::Local, false);
66 }
67 }
68 }
69 return Error::success();
70 }
71
72 private:
getSectionRange(Section & Sec)73 SectionRange &getSectionRange(Section &Sec) {
74 auto I = SectionRanges.find(&Sec);
75 if (I == SectionRanges.end())
76 I = SectionRanges.insert(std::make_pair(&Sec, SectionRange(Sec))).first;
77 return I->second;
78 }
79
80 DenseMap<Section *, SectionRange> SectionRanges;
81 SymbolIdentifierFunction F;
82 };
83
84 /// Returns a JITLink pass (as a function class) that uses the given symbol
85 /// identification function to identify external section start and end symbols
86 /// (and their associated Section*s) and transform the identified externals
87 /// into defined symbols pointing to the start of the first block in the
88 /// section and the end of the last (start and end symbols for empty sections
89 /// will be transformed into absolute symbols at address 0).
90 ///
91 /// The identification function should be callable as
92 ///
93 /// SectionRangeSymbolDesc (LinkGraph &G, Symbol &Sym)
94 ///
95 /// If Sym is not a section range start or end symbol then a default
96 /// constructed SectionRangeSymbolDesc should be returned. If Sym is a start
97 /// symbol then SectionRangeSymbolDesc(Sec, true), where Sec is a reference to
98 /// the target Section. If Sym is an end symbol then
99 /// SectionRangeSymbolDesc(Sec, false) should be returned.
100 ///
101 /// This pass should be run in the PostAllocationPass pipeline, at which point
102 /// all blocks should have been assigned their final addresses.
103 template <typename SymbolIdentifierFunction>
104 DefineExternalSectionStartAndEndSymbols<SymbolIdentifierFunction>
createDefineExternalSectionStartAndEndSymbolsPass(SymbolIdentifierFunction && F)105 createDefineExternalSectionStartAndEndSymbolsPass(
106 SymbolIdentifierFunction &&F) {
107 return DefineExternalSectionStartAndEndSymbols<SymbolIdentifierFunction>(
108 std::forward<SymbolIdentifierFunction>(F));
109 }
110
111 /// ELF section start/end symbol detection.
112 inline SectionRangeSymbolDesc
identifyELFSectionStartAndEndSymbols(LinkGraph & G,Symbol & Sym)113 identifyELFSectionStartAndEndSymbols(LinkGraph &G, Symbol &Sym) {
114 constexpr StringRef StartSymbolPrefix = "__start_";
115 constexpr StringRef EndSymbolPrefix = "__stop_";
116
117 auto SymName = Sym.getName();
118 if (SymName.starts_with(StartSymbolPrefix)) {
119 if (auto *Sec =
120 G.findSectionByName(SymName.drop_front(StartSymbolPrefix.size())))
121 return {*Sec, true};
122 } else if (SymName.starts_with(EndSymbolPrefix)) {
123 if (auto *Sec =
124 G.findSectionByName(SymName.drop_front(EndSymbolPrefix.size())))
125 return {*Sec, false};
126 }
127 return {};
128 }
129
130 /// MachO section start/end symbol detection.
131 inline SectionRangeSymbolDesc
identifyMachOSectionStartAndEndSymbols(LinkGraph & G,Symbol & Sym)132 identifyMachOSectionStartAndEndSymbols(LinkGraph &G, Symbol &Sym) {
133 constexpr StringRef StartSymbolPrefix = "section$start$";
134 constexpr StringRef EndSymbolPrefix = "section$end$";
135
136 auto SymName = Sym.getName();
137 if (SymName.starts_with(StartSymbolPrefix)) {
138 auto [SegName, SecName] =
139 SymName.drop_front(StartSymbolPrefix.size()).split('$');
140 std::string SectionName = (SegName + "," + SecName).str();
141 if (auto *Sec = G.findSectionByName(SectionName))
142 return {*Sec, true};
143 } else if (SymName.starts_with(EndSymbolPrefix)) {
144 auto [SegName, SecName] =
145 SymName.drop_front(EndSymbolPrefix.size()).split('$');
146 std::string SectionName = (SegName + "," + SecName).str();
147 if (auto *Sec = G.findSectionByName(SectionName))
148 return {*Sec, false};
149 }
150 return {};
151 }
152
153 } // end namespace jitlink
154 } // end namespace llvm
155
156 #undef DEBUG_TYPE
157
158 #endif // LLVM_EXECUTIONENGINE_JITLINK_DEFINEEXTERNALSECTIONSTARTANDENDSYMBOLS_H
159