| // icf.cc -- Identical Code Folding. | |
| // | |
| // Copyright 2009, 2010, 2011 Free Software Foundation, Inc. | |
| // Written by Sriraman Tallam <tmsriram@google.com>. | |
| // This file is part of gold. | |
| // This program is free software; you can redistribute it and/or modify | |
| // it under the terms of the GNU General Public License as published by | |
| // the Free Software Foundation; either version 3 of the License, or | |
| // (at your option) any later version. | |
| // This program is distributed in the hope that it will be useful, | |
| // but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
| // GNU General Public License for more details. | |
| // You should have received a copy of the GNU General Public License | |
| // along with this program; if not, write to the Free Software | |
| // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, | |
| // MA 02110-1301, USA. | |
| // Identical Code Folding Algorithm | |
| // ---------------------------------- | |
| // Detecting identical functions is done here and the basic algorithm | |
| // is as follows. A checksum is computed on each foldable section using | |
| // its contents and relocations. If the symbol name corresponding to | |
| // a relocation is known it is used to compute the checksum. If the | |
| // symbol name is not known the stringified name of the object and the | |
| // section number pointed to by the relocation is used. The checksums | |
| // are stored as keys in a hash map and a section is identical to some | |
| // other section if its checksum is already present in the hash map. | |
| // Checksum collisions are handled by using a multimap and explicitly | |
| // checking the contents when two sections have the same checksum. | |
| // | |
| // However, two functions A and B with identical text but with | |
| // relocations pointing to different foldable sections can be identical if | |
| // the corresponding foldable sections to which their relocations point to | |
| // turn out to be identical. Hence, this checksumming process must be | |
| // done repeatedly until convergence is obtained. Here is an example for | |
| // the following case : | |
| // | |
| // int funcA () int funcB () | |
| // { { | |
| // return foo(); return goo(); | |
| // } } | |
| // | |
| // The functions funcA and funcB are identical if functions foo() and | |
| // goo() are identical. | |
| // | |
| // Hence, as described above, we repeatedly do the checksumming, | |
| // assigning identical functions to the same group, until convergence is | |
| // obtained. Now, we have two different ways to do this depending on how | |
| // we initialize. | |
| // | |
| // Algorithm I : | |
| // ----------- | |
| // We can start with marking all functions as different and repeatedly do | |
| // the checksumming. This has the advantage that we do not need to wait | |
| // for convergence. We can stop at any point and correctness will be | |
| // guaranteed although not all cases would have been found. However, this | |
| // has a problem that some cases can never be found even if it is run until | |
| // convergence. Here is an example with mutually recursive functions : | |
| // | |
| // int funcA (int a) int funcB (int a) | |
| // { { | |
| // if (a == 1) if (a == 1) | |
| // return 1; return 1; | |
| // return 1 + funcB(a - 1); return 1 + funcA(a - 1); | |
| // } } | |
| // | |
| // In this example funcA and funcB are identical and one of them could be | |
| // folded into the other. However, if we start with assuming that funcA | |
| // and funcB are not identical, the algorithm, even after it is run to | |
| // convergence, cannot detect that they are identical. It should be noted | |
| // that even if the functions were self-recursive, Algorithm I cannot catch | |
| // that they are identical, at least as is. | |
| // | |
| // Algorithm II : | |
| // ------------ | |
| // Here we start with marking all functions as identical and then repeat | |
| // the checksumming until convergence. This can detect the above case | |
| // mentioned above. It can detect all cases that Algorithm I can and more. | |
| // However, the caveat is that it has to be run to convergence. It cannot | |
| // be stopped arbitrarily like Algorithm I as correctness cannot be | |
| // guaranteed. Algorithm II is not implemented. | |
| // | |
| // Algorithm I is used because experiments show that about three | |
| // iterations are more than enough to achieve convergence. Algorithm I can | |
| // handle recursive calls if it is changed to use a special common symbol | |
| // for recursive relocs. This seems to be the most common case that | |
| // Algorithm I could not catch as is. Mutually recursive calls are not | |
| // frequent and Algorithm I wins because of its ability to be stopped | |
| // arbitrarily. | |
| // | |
| // Caveat with using function pointers : | |
| // ------------------------------------ | |
| // | |
| // Programs using function pointer comparisons/checks should use function | |
| // folding with caution as the result of such comparisons could be different | |
| // when folding takes place. This could lead to unexpected run-time | |
| // behaviour. | |
| // | |
| // Safe Folding : | |
| // ------------ | |
| // | |
| // ICF in safe mode folds only ctors and dtors if their function pointers can | |
| // never be taken. Also, for X86-64, safe folding uses the relocation | |
| // type to determine if a function's pointer is taken or not and only folds | |
| // functions whose pointers are definitely not taken. | |
| // | |
| // Caveat with safe folding : | |
| // ------------------------ | |
| // | |
| // This applies only to x86_64. | |
| // | |
| // Position independent executables are created from PIC objects (compiled | |
| // with -fPIC) and/or PIE objects (compiled with -fPIE). For PIE objects, the | |
| // relocation types for function pointer taken and a call are the same. | |
| // Now, it is not always possible to tell if an object used in the link of | |
| // a pie executable is a PIC object or a PIE object. Hence, for pie | |
| // executables, using relocation types to disambiguate function pointers is | |
| // currently disabled. | |
| // | |
| // Further, it is not correct to use safe folding to build non-pie | |
| // executables using PIC/PIE objects. PIC/PIE objects have different | |
| // relocation types for function pointers than non-PIC objects, and the | |
| // current implementation of safe folding does not handle those relocation | |
| // types. Hence, if used, functions whose pointers are taken could still be | |
| // folded causing unpredictable run-time behaviour if the pointers were used | |
| // in comparisons. | |
| // | |
| // | |
| // | |
| // How to run : --icf=[safe|all|none] | |
| // Optional parameters : --icf-iterations <num> --print-icf-sections | |
| // | |
| // Performance : Less than 20 % link-time overhead on industry strength | |
| // applications. Up to 6 % text size reductions. | |
| #include "gold.h" | |
| #include "object.h" | |
| #include "gc.h" | |
| #include "icf.h" | |
| #include "symtab.h" | |
| #include "libiberty.h" | |
| #include "demangle.h" | |
| #include "elfcpp.h" | |
| #include "int_encoding.h" | |
| namespace gold | |
| { | |
| // This function determines if a section or a group of identical | |
| // sections has unique contents. Such unique sections or groups can be | |
| // declared final and need not be processed any further. | |
| // Parameters : | |
| // ID_SECTION : Vector mapping a section index to a Section_id pair. | |
| // IS_SECN_OR_GROUP_UNIQUE : To check if a section or a group of identical | |
| // sections is already known to be unique. | |
| // SECTION_CONTENTS : Contains the section's text and relocs to sections | |
| // that cannot be folded. SECTION_CONTENTS are NULL | |
| // implies that this function is being called for the | |
| // first time before the first iteration of icf. | |
| static void | |
| preprocess_for_unique_sections(const std::vector<Section_id>& id_section, | |
| std::vector<bool>* is_secn_or_group_unique, | |
| std::vector<std::string>* section_contents) | |
| { | |
| Unordered_map<uint32_t, unsigned int> uniq_map; | |
| std::pair<Unordered_map<uint32_t, unsigned int>::iterator, bool> | |
| uniq_map_insert; | |
| for (unsigned int i = 0; i < id_section.size(); i++) | |
| { | |
| if ((*is_secn_or_group_unique)[i]) | |
| continue; | |
| uint32_t cksum; | |
| Section_id secn = id_section[i]; | |
| section_size_type plen; | |
| if (section_contents == NULL) | |
| { | |
| // Lock the object so we can read from it. This is only called | |
| // single-threaded from queue_middle_tasks, so it is OK to lock. | |
| // Unfortunately we have no way to pass in a Task token. | |
| const Task* dummy_task = reinterpret_cast<const Task*>(-1); | |
| Task_lock_obj<Object> tl(dummy_task, secn.first); | |
| const unsigned char* contents; | |
| contents = secn.first->section_contents(secn.second, | |
| &plen, | |
| false); | |
| cksum = xcrc32(contents, plen, 0xffffffff); | |
| } | |
| else | |
| { | |
| const unsigned char* contents_array = reinterpret_cast | |
| <const unsigned char*>((*section_contents)[i].c_str()); | |
| cksum = xcrc32(contents_array, (*section_contents)[i].length(), | |
| 0xffffffff); | |
| } | |
| uniq_map_insert = uniq_map.insert(std::make_pair(cksum, i)); | |
| if (uniq_map_insert.second) | |
| { | |
| (*is_secn_or_group_unique)[i] = true; | |
| } | |
| else | |
| { | |
| (*is_secn_or_group_unique)[i] = false; | |
| (*is_secn_or_group_unique)[uniq_map_insert.first->second] = false; | |
| } | |
| } | |
| } | |
| // This returns the buffer containing the section's contents, both | |
| // text and relocs. Relocs are differentiated as those pointing to | |
| // sections that could be folded and those that cannot. Only relocs | |
| // pointing to sections that could be folded are recomputed on | |
| // subsequent invocations of this function. | |
| // Parameters : | |
| // FIRST_ITERATION : true if it is the first invocation. | |
| // SECN : Section for which contents are desired. | |
| // SECTION_NUM : Unique section number of this section. | |
| // NUM_TRACKED_RELOCS : Vector reference to store the number of relocs | |
| // to ICF sections. | |
| // KEPT_SECTION_ID : Vector which maps folded sections to kept sections. | |
| // SECTION_CONTENTS : Store the section's text and relocs to non-ICF | |
| // sections. | |
| static std::string | |
| get_section_contents(bool first_iteration, | |
| const Section_id& secn, | |
| unsigned int section_num, | |
| unsigned int* num_tracked_relocs, | |
| Symbol_table* symtab, | |
| const std::vector<unsigned int>& kept_section_id, | |
| std::vector<std::string>* section_contents) | |
| { | |
| // Lock the object so we can read from it. This is only called | |
| // single-threaded from queue_middle_tasks, so it is OK to lock. | |
| // Unfortunately we have no way to pass in a Task token. | |
| const Task* dummy_task = reinterpret_cast<const Task*>(-1); | |
| Task_lock_obj<Object> tl(dummy_task, secn.first); | |
| section_size_type plen; | |
| const unsigned char* contents = NULL; | |
| if (first_iteration) | |
| contents = secn.first->section_contents(secn.second, &plen, false); | |
| // The buffer to hold all the contents including relocs. A checksum | |
| // is then computed on this buffer. | |
| std::string buffer; | |
| std::string icf_reloc_buffer; | |
| if (num_tracked_relocs) | |
| *num_tracked_relocs = 0; | |
| Icf::Reloc_info_list& reloc_info_list = | |
| symtab->icf()->reloc_info_list(); | |
| Icf::Reloc_info_list::iterator it_reloc_info_list = | |
| reloc_info_list.find(secn); | |
| buffer.clear(); | |
| icf_reloc_buffer.clear(); | |
| // Process relocs and put them into the buffer. | |
| if (it_reloc_info_list != reloc_info_list.end()) | |
| { | |
| Icf::Sections_reachable_info v = | |
| (it_reloc_info_list->second).section_info; | |
| // Stores the information of the symbol pointed to by the reloc. | |
| Icf::Symbol_info s = (it_reloc_info_list->second).symbol_info; | |
| // Stores the addend and the symbol value. | |
| Icf::Addend_info a = (it_reloc_info_list->second).addend_info; | |
| // Stores the offset of the reloc. | |
| Icf::Offset_info o = (it_reloc_info_list->second).offset_info; | |
| Icf::Reloc_addend_size_info reloc_addend_size_info = | |
| (it_reloc_info_list->second).reloc_addend_size_info; | |
| Icf::Sections_reachable_info::iterator it_v = v.begin(); | |
| Icf::Symbol_info::iterator it_s = s.begin(); | |
| Icf::Addend_info::iterator it_a = a.begin(); | |
| Icf::Offset_info::iterator it_o = o.begin(); | |
| Icf::Reloc_addend_size_info::iterator it_addend_size = | |
| reloc_addend_size_info.begin(); | |
| for (; it_v != v.end(); ++it_v, ++it_s, ++it_a, ++it_o, ++it_addend_size) | |
| { | |
| if (first_iteration | |
| && it_v->first != NULL) | |
| { | |
| Symbol_location loc; | |
| loc.object = it_v->first; | |
| loc.shndx = it_v->second; | |
| loc.offset = convert_types<off_t, long long>(it_a->first | |
| + it_a->second); | |
| // Look through function descriptors | |
| parameters->target().function_location(&loc); | |
| if (loc.shndx != it_v->second) | |
| { | |
| it_v->second = loc.shndx; | |
| // Modify symvalue/addend to the code entry. | |
| it_a->first = loc.offset; | |
| it_a->second = 0; | |
| } | |
| } | |
| // ADDEND_STR stores the symbol value and addend and offset, | |
| // each at most 16 hex digits long. it_a points to a pair | |
| // where first is the symbol value and second is the | |
| // addend. | |
| char addend_str[50]; | |
| // It would be nice if we could use format macros in inttypes.h | |
| // here but there are not in ISO/IEC C++ 1998. | |
| snprintf(addend_str, sizeof(addend_str), "%llx %llx %llux", | |
| static_cast<long long>((*it_a).first), | |
| static_cast<long long>((*it_a).second), | |
| static_cast<unsigned long long>(*it_o)); | |
| // If the symbol pointed to by the reloc is not in an ordinary | |
| // section or if the symbol type is not FROM_OBJECT, then the | |
| // object is NULL. | |
| if (it_v->first == NULL) | |
| { | |
| if (first_iteration) | |
| { | |
| // If the symbol name is available, use it. | |
| if ((*it_s) != NULL) | |
| buffer.append((*it_s)->name()); | |
| // Append the addend. | |
| buffer.append(addend_str); | |
| buffer.append("@"); | |
| } | |
| continue; | |
| } | |
| Section_id reloc_secn(it_v->first, it_v->second); | |
| // If this reloc turns back and points to the same section, | |
| // like a recursive call, use a special symbol to mark this. | |
| if (reloc_secn.first == secn.first | |
| && reloc_secn.second == secn.second) | |
| { | |
| if (first_iteration) | |
| { | |
| buffer.append("R"); | |
| buffer.append(addend_str); | |
| buffer.append("@"); | |
| } | |
| continue; | |
| } | |
| Icf::Uniq_secn_id_map& section_id_map = | |
| symtab->icf()->section_to_int_map(); | |
| Icf::Uniq_secn_id_map::iterator section_id_map_it = | |
| section_id_map.find(reloc_secn); | |
| bool is_sym_preemptible = (*it_s != NULL | |
| && !(*it_s)->is_from_dynobj() | |
| && !(*it_s)->is_undefined() | |
| && (*it_s)->is_preemptible()); | |
| if (!is_sym_preemptible | |
| && section_id_map_it != section_id_map.end()) | |
| { | |
| // This is a reloc to a section that might be folded. | |
| if (num_tracked_relocs) | |
| (*num_tracked_relocs)++; | |
| char kept_section_str[10]; | |
| unsigned int secn_id = section_id_map_it->second; | |
| snprintf(kept_section_str, sizeof(kept_section_str), "%u", | |
| kept_section_id[secn_id]); | |
| if (first_iteration) | |
| { | |
| buffer.append("ICF_R"); | |
| buffer.append(addend_str); | |
| } | |
| icf_reloc_buffer.append(kept_section_str); | |
| // Append the addend. | |
| icf_reloc_buffer.append(addend_str); | |
| icf_reloc_buffer.append("@"); | |
| } | |
| else | |
| { | |
| // This is a reloc to a section that cannot be folded. | |
| // Process it only in the first iteration. | |
| if (!first_iteration) | |
| continue; | |
| uint64_t secn_flags = (it_v->first)->section_flags(it_v->second); | |
| // This reloc points to a merge section. Hash the | |
| // contents of this section. | |
| if ((secn_flags & elfcpp::SHF_MERGE) != 0 | |
| && parameters->target().can_icf_inline_merge_sections()) | |
| { | |
| uint64_t entsize = | |
| (it_v->first)->section_entsize(it_v->second); | |
| long long offset = it_a->first; | |
| unsigned long long addend = it_a->second; | |
| // Ignoring the addend when it is a negative value. See the | |
| // comments in Merged_symbol_value::Value in object.h. | |
| if (addend < 0xffffff00) | |
| offset = offset + addend; | |
| // For SHT_REL relocation sections, the addend is stored in the | |
| // text section at the relocation offset. | |
| uint64_t reloc_addend_value = 0; | |
| const unsigned char* reloc_addend_ptr = | |
| contents + static_cast<unsigned long long>(*it_o); | |
| switch(*it_addend_size) | |
| { | |
| case 0: | |
| { | |
| break; | |
| } | |
| case 1: | |
| { | |
| reloc_addend_value = | |
| read_from_pointer<8>(reloc_addend_ptr); | |
| break; | |
| } | |
| case 2: | |
| { | |
| reloc_addend_value = | |
| read_from_pointer<16>(reloc_addend_ptr); | |
| break; | |
| } | |
| case 4: | |
| { | |
| reloc_addend_value = | |
| read_from_pointer<32>(reloc_addend_ptr); | |
| break; | |
| } | |
| case 8: | |
| { | |
| reloc_addend_value = | |
| read_from_pointer<64>(reloc_addend_ptr); | |
| break; | |
| } | |
| default: | |
| gold_unreachable(); | |
| } | |
| offset = offset + reloc_addend_value; | |
| section_size_type secn_len; | |
| const unsigned char* str_contents = | |
| (it_v->first)->section_contents(it_v->second, | |
| &secn_len, | |
| false) + offset; | |
| if ((secn_flags & elfcpp::SHF_STRINGS) != 0) | |
| { | |
| // String merge section. | |
| const char* str_char = | |
| reinterpret_cast<const char*>(str_contents); | |
| switch(entsize) | |
| { | |
| case 1: | |
| { | |
| buffer.append(str_char); | |
| break; | |
| } | |
| case 2: | |
| { | |
| const uint16_t* ptr_16 = | |
| reinterpret_cast<const uint16_t*>(str_char); | |
| unsigned int strlen_16 = 0; | |
| // Find the NULL character. | |
| while(*(ptr_16 + strlen_16) != 0) | |
| strlen_16++; | |
| buffer.append(str_char, strlen_16 * 2); | |
| } | |
| break; | |
| case 4: | |
| { | |
| const uint32_t* ptr_32 = | |
| reinterpret_cast<const uint32_t*>(str_char); | |
| unsigned int strlen_32 = 0; | |
| // Find the NULL character. | |
| while(*(ptr_32 + strlen_32) != 0) | |
| strlen_32++; | |
| buffer.append(str_char, strlen_32 * 4); | |
| } | |
| break; | |
| default: | |
| gold_unreachable(); | |
| } | |
| } | |
| else | |
| { | |
| // Use the entsize to determine the length. | |
| buffer.append(reinterpret_cast<const | |
| char*>(str_contents), | |
| entsize); | |
| } | |
| buffer.append("@"); | |
| } | |
| else if ((*it_s) != NULL) | |
| { | |
| // If symbol name is available use that. | |
| buffer.append((*it_s)->name()); | |
| // Append the addend. | |
| buffer.append(addend_str); | |
| buffer.append("@"); | |
| } | |
| else | |
| { | |
| // Symbol name is not available, like for a local symbol, | |
| // use object and section id. | |
| buffer.append(it_v->first->name()); | |
| char secn_id[10]; | |
| snprintf(secn_id, sizeof(secn_id), "%u",it_v->second); | |
| buffer.append(secn_id); | |
| // Append the addend. | |
| buffer.append(addend_str); | |
| buffer.append("@"); | |
| } | |
| } | |
| } | |
| } | |
| if (first_iteration) | |
| { | |
| buffer.append("Contents = "); | |
| buffer.append(reinterpret_cast<const char*>(contents), plen); | |
| // Store the section contents that dont change to avoid recomputing | |
| // during the next call to this function. | |
| (*section_contents)[section_num] = buffer; | |
| } | |
| else | |
| { | |
| gold_assert(buffer.empty()); | |
| // Reuse the contents computed in the previous iteration. | |
| buffer.append((*section_contents)[section_num]); | |
| } | |
| buffer.append(icf_reloc_buffer); | |
| return buffer; | |
| } | |
| // This function computes a checksum on each section to detect and form | |
| // groups of identical sections. The first iteration does this for all | |
| // sections. | |
| // Further iterations do this only for the kept sections from each group to | |
| // determine if larger groups of identical sections could be formed. The | |
| // first section in each group is the kept section for that group. | |
| // | |
| // CRC32 is the checksumming algorithm and can have collisions. That is, | |
| // two sections with different contents can have the same checksum. Hence, | |
| // a multimap is used to maintain more than one group of checksum | |
| // identical sections. A section is added to a group only after its | |
| // contents are explicitly compared with the kept section of the group. | |
| // | |
| // Parameters : | |
| // ITERATION_NUM : Invocation instance of this function. | |
| // NUM_TRACKED_RELOCS : Vector reference to store the number of relocs | |
| // to ICF sections. | |
| // KEPT_SECTION_ID : Vector which maps folded sections to kept sections. | |
| // ID_SECTION : Vector mapping a section to an unique integer. | |
| // IS_SECN_OR_GROUP_UNIQUE : To check if a section or a group of identical | |
| // sections is already known to be unique. | |
| // SECTION_CONTENTS : Store the section's text and relocs to non-ICF | |
| // sections. | |
| static bool | |
| match_sections(unsigned int iteration_num, | |
| Symbol_table* symtab, | |
| std::vector<unsigned int>* num_tracked_relocs, | |
| std::vector<unsigned int>* kept_section_id, | |
| const std::vector<Section_id>& id_section, | |
| std::vector<bool>* is_secn_or_group_unique, | |
| std::vector<std::string>* section_contents) | |
| { | |
| Unordered_multimap<uint32_t, unsigned int> section_cksum; | |
| std::pair<Unordered_multimap<uint32_t, unsigned int>::iterator, | |
| Unordered_multimap<uint32_t, unsigned int>::iterator> key_range; | |
| bool converged = true; | |
| if (iteration_num == 1) | |
| preprocess_for_unique_sections(id_section, | |
| is_secn_or_group_unique, | |
| NULL); | |
| else | |
| preprocess_for_unique_sections(id_section, | |
| is_secn_or_group_unique, | |
| section_contents); | |
| std::vector<std::string> full_section_contents; | |
| for (unsigned int i = 0; i < id_section.size(); i++) | |
| { | |
| full_section_contents.push_back(""); | |
| if ((*is_secn_or_group_unique)[i]) | |
| continue; | |
| Section_id secn = id_section[i]; | |
| std::string this_secn_contents; | |
| uint32_t cksum; | |
| if (iteration_num == 1) | |
| { | |
| unsigned int num_relocs = 0; | |
| this_secn_contents = get_section_contents(true, secn, i, &num_relocs, | |
| symtab, (*kept_section_id), | |
| section_contents); | |
| (*num_tracked_relocs)[i] = num_relocs; | |
| } | |
| else | |
| { | |
| if ((*kept_section_id)[i] != i) | |
| { | |
| // This section is already folded into something. See | |
| // if it should point to a different kept section. | |
| unsigned int kept_section = (*kept_section_id)[i]; | |
| if (kept_section != (*kept_section_id)[kept_section]) | |
| { | |
| (*kept_section_id)[i] = (*kept_section_id)[kept_section]; | |
| } | |
| continue; | |
| } | |
| this_secn_contents = get_section_contents(false, secn, i, NULL, | |
| symtab, (*kept_section_id), | |
| section_contents); | |
| } | |
| const unsigned char* this_secn_contents_array = | |
| reinterpret_cast<const unsigned char*>(this_secn_contents.c_str()); | |
| cksum = xcrc32(this_secn_contents_array, this_secn_contents.length(), | |
| 0xffffffff); | |
| size_t count = section_cksum.count(cksum); | |
| if (count == 0) | |
| { | |
| // Start a group with this cksum. | |
| section_cksum.insert(std::make_pair(cksum, i)); | |
| full_section_contents[i] = this_secn_contents; | |
| } | |
| else | |
| { | |
| key_range = section_cksum.equal_range(cksum); | |
| Unordered_multimap<uint32_t, unsigned int>::iterator it; | |
| // Search all the groups with this cksum for a match. | |
| for (it = key_range.first; it != key_range.second; ++it) | |
| { | |
| unsigned int kept_section = it->second; | |
| if (full_section_contents[kept_section].length() | |
| != this_secn_contents.length()) | |
| continue; | |
| if (memcmp(full_section_contents[kept_section].c_str(), | |
| this_secn_contents.c_str(), | |
| this_secn_contents.length()) != 0) | |
| continue; | |
| (*kept_section_id)[i] = kept_section; | |
| converged = false; | |
| break; | |
| } | |
| if (it == key_range.second) | |
| { | |
| // Create a new group for this cksum. | |
| section_cksum.insert(std::make_pair(cksum, i)); | |
| full_section_contents[i] = this_secn_contents; | |
| } | |
| } | |
| // If there are no relocs to foldable sections do not process | |
| // this section any further. | |
| if (iteration_num == 1 && (*num_tracked_relocs)[i] == 0) | |
| (*is_secn_or_group_unique)[i] = true; | |
| } | |
| return converged; | |
| } | |
| // During safe icf (--icf=safe), only fold functions that are ctors or dtors. | |
| // This function returns true if the section name is that of a ctor or a dtor. | |
| static bool | |
| is_function_ctor_or_dtor(const std::string& section_name) | |
| { | |
| const char* mangled_func_name = strrchr(section_name.c_str(), '.'); | |
| gold_assert(mangled_func_name != NULL); | |
| if ((is_prefix_of("._ZN", mangled_func_name) | |
| || is_prefix_of("._ZZ", mangled_func_name)) | |
| && (is_gnu_v3_mangled_ctor(mangled_func_name + 1) | |
| || is_gnu_v3_mangled_dtor(mangled_func_name + 1))) | |
| { | |
| return true; | |
| } | |
| return false; | |
| } | |
| // This is the main ICF function called in gold.cc. This does the | |
| // initialization and calls match_sections repeatedly (twice by default) | |
| // which computes the crc checksums and detects identical functions. | |
| void | |
| Icf::find_identical_sections(const Input_objects* input_objects, | |
| Symbol_table* symtab) | |
| { | |
| unsigned int section_num = 0; | |
| std::vector<unsigned int> num_tracked_relocs; | |
| std::vector<bool> is_secn_or_group_unique; | |
| std::vector<std::string> section_contents; | |
| const Target& target = parameters->target(); | |
| // Decide which sections are possible candidates first. | |
| for (Input_objects::Relobj_iterator p = input_objects->relobj_begin(); | |
| p != input_objects->relobj_end(); | |
| ++p) | |
| { | |
| // Lock the object so we can read from it. This is only called | |
| // single-threaded from queue_middle_tasks, so it is OK to lock. | |
| // Unfortunately we have no way to pass in a Task token. | |
| const Task* dummy_task = reinterpret_cast<const Task*>(-1); | |
| Task_lock_obj<Object> tl(dummy_task, *p); | |
| for (unsigned int i = 0;i < (*p)->shnum(); ++i) | |
| { | |
| const std::string section_name = (*p)->section_name(i); | |
| if (!is_section_foldable_candidate(section_name)) | |
| continue; | |
| if (!(*p)->is_section_included(i)) | |
| continue; | |
| if (parameters->options().gc_sections() | |
| && symtab->gc()->is_section_garbage(*p, i)) | |
| continue; | |
| // With --icf=safe, check if the mangled function name is a ctor | |
| // or a dtor. The mangled function name can be obtained from the | |
| // section name by stripping the section prefix. | |
| if (parameters->options().icf_safe_folding() | |
| && !is_function_ctor_or_dtor(section_name) | |
| && (!target.can_check_for_function_pointers() | |
| || section_has_function_pointers(*p, i))) | |
| { | |
| continue; | |
| } | |
| this->id_section_.push_back(Section_id(*p, i)); | |
| this->section_id_[Section_id(*p, i)] = section_num; | |
| this->kept_section_id_.push_back(section_num); | |
| num_tracked_relocs.push_back(0); | |
| is_secn_or_group_unique.push_back(false); | |
| section_contents.push_back(""); | |
| section_num++; | |
| } | |
| } | |
| unsigned int num_iterations = 0; | |
| // Default number of iterations to run ICF is 2. | |
| unsigned int max_iterations = (parameters->options().icf_iterations() > 0) | |
| ? parameters->options().icf_iterations() | |
| : 2; | |
| bool converged = false; | |
| while (!converged && (num_iterations < max_iterations)) | |
| { | |
| num_iterations++; | |
| converged = match_sections(num_iterations, symtab, | |
| &num_tracked_relocs, &this->kept_section_id_, | |
| this->id_section_, &is_secn_or_group_unique, | |
| §ion_contents); | |
| } | |
| if (parameters->options().print_icf_sections()) | |
| { | |
| if (converged) | |
| gold_info(_("%s: ICF Converged after %u iteration(s)"), | |
| program_name, num_iterations); | |
| else | |
| gold_info(_("%s: ICF stopped after %u iteration(s)"), | |
| program_name, num_iterations); | |
| } | |
| // Unfold --keep-unique symbols. | |
| for (options::String_set::const_iterator p = | |
| parameters->options().keep_unique_begin(); | |
| p != parameters->options().keep_unique_end(); | |
| ++p) | |
| { | |
| const char* name = p->c_str(); | |
| Symbol* sym = symtab->lookup(name); | |
| if (sym == NULL) | |
| { | |
| gold_warning(_("Could not find symbol %s to unfold\n"), name); | |
| } | |
| else if (sym->source() == Symbol::FROM_OBJECT | |
| && !sym->object()->is_dynamic()) | |
| { | |
| Object* obj = sym->object(); | |
| bool is_ordinary; | |
| unsigned int shndx = sym->shndx(&is_ordinary); | |
| if (is_ordinary) | |
| { | |
| this->unfold_section(obj, shndx); | |
| } | |
| } | |
| } | |
| this->icf_ready(); | |
| } | |
| // Unfolds the section denoted by OBJ and SHNDX if folded. | |
| void | |
| Icf::unfold_section(Object* obj, unsigned int shndx) | |
| { | |
| Section_id secn(obj, shndx); | |
| Uniq_secn_id_map::iterator it = this->section_id_.find(secn); | |
| if (it == this->section_id_.end()) | |
| return; | |
| unsigned int section_num = it->second; | |
| unsigned int kept_section_id = this->kept_section_id_[section_num]; | |
| if (kept_section_id != section_num) | |
| this->kept_section_id_[section_num] = section_num; | |
| } | |
| // This function determines if the section corresponding to the | |
| // given object and index is folded based on if the kept section | |
| // is different from this section. | |
| bool | |
| Icf::is_section_folded(Object* obj, unsigned int shndx) | |
| { | |
| Section_id secn(obj, shndx); | |
| Uniq_secn_id_map::iterator it = this->section_id_.find(secn); | |
| if (it == this->section_id_.end()) | |
| return false; | |
| unsigned int section_num = it->second; | |
| unsigned int kept_section_id = this->kept_section_id_[section_num]; | |
| return kept_section_id != section_num; | |
| } | |
| // This function returns the folded section for the given section. | |
| Section_id | |
| Icf::get_folded_section(Object* dup_obj, unsigned int dup_shndx) | |
| { | |
| Section_id dup_secn(dup_obj, dup_shndx); | |
| Uniq_secn_id_map::iterator it = this->section_id_.find(dup_secn); | |
| gold_assert(it != this->section_id_.end()); | |
| unsigned int section_num = it->second; | |
| unsigned int kept_section_id = this->kept_section_id_[section_num]; | |
| Section_id folded_section = this->id_section_[kept_section_id]; | |
| return folded_section; | |
| } | |
| } // End of namespace gold. |