X-Git-Url: https://oss.titaniummirror.com/gitweb?p=msp430-binutils.git;a=blobdiff_plain;f=gold%2Ficf.cc;fp=gold%2Ficf.cc;h=03b927adc40de763a486d85395cab9ffddd7fdc9;hp=0000000000000000000000000000000000000000;hb=d5da4f291af551c0b8b79e1d4a9b173d60e5c10e;hpb=7b5ea4fcdf2819e070665ab5610f8b48e3867c10 diff --git a/gold/icf.cc b/gold/icf.cc new file mode 100644 index 0000000..03b927a --- /dev/null +++ b/gold/icf.cc @@ -0,0 +1,697 @@ +// icf.cc -- Identical Code Folding. +// +// Copyright 2009 Free Software Foundation, Inc. +// Written by Sriraman Tallam . + +// 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 .text 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 .text sections can be identical if +// the corresponding .text 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. +// +// +// How to run : --icf +// Optional parameters : --icf-iterations --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" + +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& id_section, + std::vector* is_secn_or_group_unique, + std::vector* section_contents) +{ + Unordered_map uniq_map; + std::pair::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) + { + 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 + ((*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& kept_section_id, + std::vector* section_contents) +{ + 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::Section_list& seclist = symtab->icf()->section_reloc_list(); + Icf::Symbol_list& symlist = symtab->icf()->symbol_reloc_list(); + Icf::Addend_list& addendlist = symtab->icf()->addend_reloc_list(); + + Icf::Section_list::iterator it_seclist = seclist.find(secn); + Icf::Symbol_list::iterator it_symlist = symlist.find(secn); + Icf::Addend_list::iterator it_addendlist = addendlist.find(secn); + + buffer.clear(); + icf_reloc_buffer.clear(); + + // Process relocs and put them into the buffer. + + if (it_seclist != seclist.end()) + { + gold_assert(it_symlist != symlist.end()); + gold_assert(it_addendlist != addendlist.end()); + Icf::Sections_reachable_list v = it_seclist->second; + Icf::Symbol_info s = it_symlist->second; + Icf::Addend_info a = it_addendlist->second; + Icf::Sections_reachable_list::iterator it_v = v.begin(); + Icf::Symbol_info::iterator it_s = s.begin(); + Icf::Addend_info::iterator it_a = a.begin(); + + for (; it_v != v.end(); ++it_v, ++it_s, ++it_a) + { + // ADDEND_STR stores the symbol value and addend, each + // atmost 16 hex digits long. it_v points to a pair + // where first is the symbol value and second is the + // addend. + char addend_str[34]; + snprintf(addend_str, sizeof(addend_str), "%llx %llx", + (*it_a).first, (*it_a).second); + 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); + if (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) + { + uint64_t entsize = + (it_v->first)->section_entsize(it_v->second); + long long offset = it_a->first + it_a->second; + 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(str_contents); + switch(entsize) + { + case 1: + { + buffer.append(str_char); + break; + } + case 2: + { + const uint16_t* ptr_16 = + reinterpret_cast(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(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(str_contents), + entsize); + } + } + else if ((*it_s) != NULL) + { + // If symbol name is available use that. + const char *sym_name = (*it_s)->name(); + buffer.append(sym_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(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 +// sectionsis 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* num_tracked_relocs, + std::vector* kept_section_id, + const std::vector& id_section, + std::vector* is_secn_or_group_unique, + std::vector* section_contents) +{ + Unordered_multimap section_cksum; + std::pair::iterator, + Unordered_multimap::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 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(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::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 mangled function name is a ctor or a +// dtor. + +static bool +is_function_ctor_or_dtor(const char* mangled_func_name) +{ + if ((is_prefix_of("_ZN", mangled_func_name) + || is_prefix_of("_ZZ", mangled_func_name)) + && (is_gnu_v3_mangled_ctor(mangled_func_name) + || is_gnu_v3_mangled_dtor(mangled_func_name))) + { + 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 num_tracked_relocs; + std::vector is_secn_or_group_unique; + std::vector section_contents; + + // Decide which sections are possible candidates first. + + for (Input_objects::Relobj_iterator p = input_objects->relobj_begin(); + p != input_objects->relobj_end(); + ++p) + { + for (unsigned int i = 0;i < (*p)->shnum(); ++i) + { + const char* section_name = (*p)->section_name(i).c_str(); + // Only looking to fold functions, so just look at .text sections. + if (!is_prefix_of(".text.", 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 mangled name is a ctor or a dtor. + if (parameters->options().icf_safe_folding() + && !is_function_ctor_or_dtor(section_name + 6)) + 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.