1 // icf.h -- Identical Code Folding
2
3 // Copyright (C) 2009-2023 Free Software Foundation, Inc.
4 // Written by Sriraman Tallam <tmsriram@google.com>.
5
6 // This file is part of gold.
7
8 // This program is free software; you can redistribute it and/or modify
9 // it under the terms of the GNU General Public License as published by
10 // the Free Software Foundation; either version 3 of the License, or
11 // (at your option) any later version.
12
13 // This program is distributed in the hope that it will be useful,
14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 // GNU General Public License for more details.
17
18 // You should have received a copy of the GNU General Public License
19 // along with this program; if not, write to the Free Software
20 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
21 // MA 02110-1301, USA.
22
23 #ifndef GOLD_ICF_H
24 #define GOLD_ICF_H
25
26 #include <vector>
27
28 #include "elfcpp.h"
29 #include "symtab.h"
30 #include "object.h"
31
32 namespace gold
33 {
34
35 class Object;
36 class Input_objects;
37 class Symbol_table;
38
39 class Icf
40 {
41 public:
42 typedef std::vector<Section_id> Sections_reachable_info;
43 typedef std::vector<Symbol*> Symbol_info;
44 typedef std::vector<std::pair<long long, long long> > Addend_info;
45 typedef std::vector<uint64_t> Offset_info;
46 typedef std::vector<unsigned int> Reloc_addend_size_info;
47 typedef Unordered_map<Section_id,
48 unsigned int,
49 Section_id_hash> Uniq_secn_id_map;
50 typedef Unordered_set<Section_id, Section_id_hash> Secn_fptr_taken_set;
51
52 typedef struct
53 {
54 // This stores the section corresponding to the reloc.
55 Sections_reachable_info section_info;
56 // This stores the symbol corresponding to the reloc.
57 Symbol_info symbol_info;
58 // This stores the symbol value and the addend for a reloc.
59 Addend_info addend_info;
60 Offset_info offset_info;
61 Reloc_addend_size_info reloc_addend_size_info;
62 } Reloc_info;
63
64 typedef Unordered_map<Section_id, Reloc_info,
65 Section_id_hash> Reloc_info_list;
66
67 // A region of some other section that should be considered part of
68 // a section for ICF purposes. This is used to avoid folding sections
69 // that have identical text and relocations but different .eh_frame
70 // information.
71 typedef struct
72 {
73 Section_id section;
74 section_offset_type offset;
75 section_size_type length;
76 } Extra_identity_info;
77
78 typedef std::multimap<Section_id, Extra_identity_info> Extra_identity_list;
79
80 Icf()
81 : id_section_(), section_id_(), kept_section_id_(),
82 fptr_section_id_(),
83 icf_ready_(false),
84 reloc_info_list_()
85 { }
86
87 // Returns the kept folded identical section corresponding to
88 // dup_obj and dup_shndx.
89 Section_id
90 get_folded_section(Relobj* dup_obj, unsigned int dup_shndx);
91
92 // Forms groups of identical sections where the first member
93 // of each group is the kept section during folding.
94 void
95 find_identical_sections(const Input_objects* input_objects,
96 Symbol_table* symtab);
97
98 // This is set when ICF has been run and the groups of
99 // identical sections have been formed.
100 void
101 icf_ready()
102 { this->icf_ready_ = true; }
103
104 // Returns true if ICF has been run.
105 bool
106 is_icf_ready()
107 { return this->icf_ready_; }
108
109 // Unfolds the section denoted by OBJ and SHNDX if folded.
110 void
111 unfold_section(Relobj* obj, unsigned int shndx);
112
113 // Returns the kept section corresponding to the
114 // given section.
115 bool
116 is_section_folded(Relobj* obj, unsigned int shndx);
117
118 // Given an object and a section index, this returns true if the
119 // pointer of the function defined in this section is taken.
120 bool
121 section_has_function_pointers(Relobj* obj, unsigned int shndx)
122 {
123 return (this->fptr_section_id_.find(Section_id(obj, shndx))
124 != this->fptr_section_id_.end());
125 }
126
127 // Records that a pointer of the function defined in this section
128 // is taken.
129 void
130 set_section_has_function_pointers(Relobj* obj, unsigned int shndx)
131 {
132 this->fptr_section_id_.insert(Section_id(obj, shndx));
133 }
134
135 // Checks if the section_name should be searched for relocs
136 // corresponding to taken function pointers. Ignores eh_frame
137 // and vtable sections.
138 inline bool
139 check_section_for_function_pointers(const std::string& section_name,
140 Target* target)
141 {
142 return (parameters->options().icf_safe_folding()
143 && target->can_check_for_function_pointers()
144 && target->section_may_have_icf_unsafe_pointers(
145 section_name.c_str()));
146 }
147
148 // Returns a map of a section to info (Reloc_info) about its relocations.
149 Reloc_info_list&
150 reloc_info_list()
151 { return this->reloc_info_list_; }
152
153 // Returns a map from section to region of a different section that should
154 // be considered part of the key section for ICF purposes.
155 Extra_identity_list&
156 extra_identity_list()
157 { return this->extra_identity_list_; }
158
159 // Returns a mapping of each section to a unique integer.
160 Uniq_secn_id_map&
161 section_to_int_map()
162 { return this->section_id_; }
163
164 private:
165
166 bool
167 add_ehframe_links(Relobj* object, unsigned int ehframe_shndx,
168 Reloc_info& ehframe_relocs);
169
170 // Maps integers to sections.
171 std::vector<Section_id> id_section_;
172 // Does the reverse.
173 Uniq_secn_id_map section_id_;
174 // Given a section id, this maps it to the id of the kept
175 // section. If the id's are the same then this section is
176 // not folded.
177 std::vector<unsigned int> kept_section_id_;
178 // Given a section id, this says if the pointer to this
179 // function is taken in which case it is dangerous to fold
180 // this function.
181 Secn_fptr_taken_set fptr_section_id_;
182 // Flag to indicate if ICF has been run.
183 bool icf_ready_;
184 // This list is populated by gc_process_relocs in gc.h.
185 Reloc_info_list reloc_info_list_;
186 // Regions of other sections that should be considered part of
187 // each section for ICF purposes.
188 Extra_identity_list extra_identity_list_;
189 };
190
191 // This function returns true if this section corresponds to a function that
192 // should be considered by icf as a possible candidate for folding. Some
193 // earlier gcc versions, like 4.0.3, put constructors and destructors in
194 // .gnu.linkonce.t sections and hence should be included too.
195 // The mechanism used to safely fold functions referenced by .eh_frame
196 // requires folding .gcc_except_table sections as well; see "Notes regarding
197 // C++ exception handling" at the top of icf.cc for an explanation why.
198 inline bool
199 is_section_foldable_candidate(const std::string& section_name)
200 {
201 const char* section_name_cstr = section_name.c_str();
202 return (is_prefix_of(".text", section_name_cstr)
203 || is_prefix_of(".gcc_except_table", section_name_cstr)
204 || is_prefix_of(".gnu.linkonce.t", section_name_cstr));
205 }
206
207 } // End of namespace gold.
208
209 #endif