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// merge.cc -- handle section merging for gold
// Copyright (C) 2006-2024 Free Software Foundation, Inc.
// Written by Ian Lance Taylor <iant@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.
#include "gold.h"
#include <cstdlib>
#include <algorithm>
#include "merge.h"
#include "compressed_output.h"
namespace gold
{
// Class Object_merge_map.
// Destructor.
Object_merge_map::~Object_merge_map()
{
for (Section_merge_maps::iterator p = this->section_merge_maps_.begin();
p != this->section_merge_maps_.end();
++p)
delete p->second;
}
// Get the Input_merge_map to use for an input section, or NULL.
const Object_merge_map::Input_merge_map*
Object_merge_map::get_input_merge_map(unsigned int shndx) const
{
gold_assert(shndx != -1U);
const Section_merge_maps &maps = this->section_merge_maps_;
for (Section_merge_maps::const_iterator i = maps.begin(), e = maps.end();
i != e; ++i)
{
if (i->first == shndx)
return i->second;
}
return NULL;
}
// Get or create the Input_merge_map to use for an input section.
Object_merge_map::Input_merge_map*
Object_merge_map::get_or_make_input_merge_map(
const Output_section_data* output_data, unsigned int shndx) {
Input_merge_map* map = this->get_input_merge_map(shndx);
if (map != NULL)
{
// For a given input section in a given object, every mapping
// must be done with the same Merge_map.
gold_assert(map->output_data == output_data);
return map;
}
Input_merge_map* new_map = new Input_merge_map;
new_map->output_data = output_data;
Section_merge_maps &maps = this->section_merge_maps_;
maps.push_back(std::make_pair(shndx, new_map));
return new_map;
}
// Add a mapping.
void
Object_merge_map::add_mapping(const Output_section_data* output_data,
unsigned int shndx,
section_offset_type input_offset,
section_size_type length,
section_offset_type output_offset)
{
Input_merge_map* map = this->get_or_make_input_merge_map(output_data, shndx);
map->add_mapping(input_offset, length, output_offset);
}
void
Object_merge_map::Input_merge_map::add_mapping(
section_offset_type input_offset, section_size_type length,
section_offset_type output_offset) {
// Try to merge the new entry in the last one we saw.
if (!this->entries.empty())
{
Input_merge_entry& entry(this->entries.back());
// Use section_size_type to avoid signed/unsigned warnings.
section_size_type input_offset_u = input_offset;
section_size_type output_offset_u = output_offset;
// If this entry is not in order, we need to sort the vector
// before looking anything up.
if (input_offset_u < entry.input_offset + entry.length)
{
gold_assert(input_offset < entry.input_offset);
gold_assert(input_offset_u + length
<= static_cast<section_size_type>(entry.input_offset));
this->sorted = false;
}
else if (entry.input_offset + entry.length == input_offset_u
&& (output_offset == -1
? entry.output_offset == -1
: entry.output_offset + entry.length == output_offset_u))
{
entry.length += length;
return;
}
}
Input_merge_entry entry;
entry.input_offset = input_offset;
entry.length = length;
entry.output_offset = output_offset;
this->entries.push_back(entry);
}
// Get the output offset for an input address.
bool
Object_merge_map::get_output_offset(unsigned int shndx,
section_offset_type input_offset,
section_offset_type* output_offset)
{
Input_merge_map* map = this->get_input_merge_map(shndx);
if (map == NULL)
return false;
if (!map->sorted)
{
std::sort(map->entries.begin(), map->entries.end(),
Input_merge_compare());
map->sorted = true;
}
Input_merge_entry entry;
entry.input_offset = input_offset;
std::vector<Input_merge_entry>::const_iterator p =
std::upper_bound(map->entries.begin(), map->entries.end(),
entry, Input_merge_compare());
if (p == map->entries.begin())
return false;
--p;
gold_assert(p->input_offset <= input_offset);
if (input_offset - p->input_offset
>= static_cast<section_offset_type>(p->length))
return false;
*output_offset = p->output_offset;
if (*output_offset != -1)
*output_offset += (input_offset - p->input_offset);
return true;
}
// Return whether this is the merge map for section SHNDX.
const Output_section_data*
Object_merge_map::find_merge_section(unsigned int shndx) const {
const Object_merge_map::Input_merge_map* map =
this->get_input_merge_map(shndx);
if (map == NULL)
return NULL;
return map->output_data;
}
// Initialize a mapping from input offsets to output addresses.
template<int size>
void
Object_merge_map::initialize_input_to_output_map(
unsigned int shndx,
typename elfcpp::Elf_types<size>::Elf_Addr starting_address,
Unordered_map<section_offset_type,
typename elfcpp::Elf_types<size>::Elf_Addr>* initialize_map)
{
Input_merge_map* map = this->get_input_merge_map(shndx);
gold_assert(map != NULL);
gold_assert(initialize_map->empty());
// We know how many entries we are going to add.
// reserve_unordered_map takes an expected count of buckets, not a
// count of elements, so double it to try to reduce collisions.
reserve_unordered_map(initialize_map, map->entries.size() * 2);
for (Input_merge_map::Entries::const_iterator p = map->entries.begin();
p != map->entries.end();
++p)
{
section_offset_type output_offset = p->output_offset;
if (output_offset != -1)
output_offset += starting_address;
else
{
// If we see a relocation against an address we have chosen
// to discard, we relocate to zero. FIXME: We could also
// issue a warning in this case; that would require
// reporting this somehow and checking it in the routines in
// reloc.h.
output_offset = 0;
}
initialize_map->insert(std::make_pair(p->input_offset, output_offset));
}
}
// Class Output_merge_base.
// Return the output offset for an input offset. The input address is
// at offset OFFSET in section SHNDX in OBJECT. If we know the
// offset, set *POUTPUT and return true. Otherwise return false.
bool
Output_merge_base::do_output_offset(const Relobj* object,
unsigned int shndx,
section_offset_type offset,
section_offset_type* poutput) const
{
return object->merge_output_offset(shndx, offset, poutput);
}
// Record a merged input section for script processing.
void
Output_merge_base::record_input_section(Relobj* relobj, unsigned int shndx)
{
gold_assert(this->keeps_input_sections_ && relobj != NULL);
// If this is the first input section, record it. We need do this because
// this->input_sections_ is unordered.
if (this->first_relobj_ == NULL)
{
this->first_relobj_ = relobj;
this->first_shndx_ = shndx;
}
std::pair<Input_sections::iterator, bool> result =
this->input_sections_.insert(Section_id(relobj, shndx));
// We should insert a merge section once only.
gold_assert(result.second);
}
// Class Output_merge_data.
// Compute the hash code for a fixed-size constant.
size_t
Output_merge_data::Merge_data_hash::operator()(Merge_data_key k) const
{
const unsigned char* p = this->pomd_->constant(k);
section_size_type entsize =
convert_to_section_size_type(this->pomd_->entsize());
// Fowler/Noll/Vo (FNV) hash (type FNV-1a).
if (sizeof(size_t) == 8)
{
size_t result = static_cast<size_t>(14695981039346656037ULL);
for (section_size_type i = 0; i < entsize; ++i)
{
result &= (size_t) *p++;
result *= 1099511628211ULL;
}
return result;
}
else
{
size_t result = 2166136261UL;
for (section_size_type i = 0; i < entsize; ++i)
{
result ^= (size_t) *p++;
result *= 16777619UL;
}
return result;
}
}
// Return whether one hash table key equals another.
bool
Output_merge_data::Merge_data_eq::operator()(Merge_data_key k1,
Merge_data_key k2) const
{
const unsigned char* p1 = this->pomd_->constant(k1);
const unsigned char* p2 = this->pomd_->constant(k2);
return memcmp(p1, p2, this->pomd_->entsize()) == 0;
}
// Add a constant to the end of the section contents.
void
Output_merge_data::add_constant(const unsigned char* p)
{
section_size_type entsize = convert_to_section_size_type(this->entsize());
section_size_type addralign =
convert_to_section_size_type(this->addralign());
section_size_type addsize = std::max(entsize, addralign);
if (this->len_ + addsize > this->alc_)
{
if (this->alc_ == 0)
this->alc_ = 128 * addsize;
else
this->alc_ *= 2;
this->p_ = static_cast<unsigned char*>(realloc(this->p_, this->alc_));
if (this->p_ == NULL)
gold_nomem();
}
memcpy(this->p_ + this->len_, p, entsize);
if (addsize > entsize)
memset(this->p_ + this->len_ + entsize, 0, addsize - entsize);
this->len_ += addsize;
}
// Add the input section SHNDX in OBJECT to a merged output section
// which holds fixed length constants. Return whether we were able to
// handle the section; if not, it will be linked as usual without
// constant merging.
bool
Output_merge_data::do_add_input_section(Relobj* object, unsigned int shndx)
{
section_size_type len;
bool is_new;
const unsigned char* p = object->decompressed_section_contents(shndx, &len,
&is_new);
section_size_type entsize = convert_to_section_size_type(this->entsize());
if (len % entsize != 0)
{
if (is_new)
delete[] p;
return false;
}
this->input_count_ += len / entsize;
Object_merge_map* merge_map = object->get_or_create_merge_map();
Object_merge_map::Input_merge_map* input_merge_map =
merge_map->get_or_make_input_merge_map(this, shndx);
for (section_size_type i = 0; i < len; i += entsize, p += entsize)
{
// Add the constant to the section contents. If we find that it
// is already in the hash table, we will remove it again.
Merge_data_key k = this->len_;
this->add_constant(p);
std::pair<Merge_data_hashtable::iterator, bool> ins =
this->hashtable_.insert(k);
if (!ins.second)
{
// Key was already present. Remove the copy we just added.
this->len_ -= entsize;
k = *ins.first;
}
// Record the offset of this constant in the output section.
input_merge_map->add_mapping(i, entsize, k);
}
// For script processing, we keep the input sections.
if (this->keeps_input_sections())
record_input_section(object, shndx);
if (is_new)
delete[] p;
return true;
}
// Set the final data size in a merged output section with fixed size
// constants.
void
Output_merge_data::set_final_data_size()
{
// Release the memory we don't need.
this->p_ = static_cast<unsigned char*>(realloc(this->p_, this->len_));
// An Output_merge_data object may be empty and realloc is allowed
// to return a NULL pointer in this case. An Output_merge_data is empty
// if all its input sections have sizes that are not multiples of entsize.
gold_assert(this->p_ != NULL || this->len_ == 0);
this->set_data_size(this->len_);
}
// Write the data of a merged output section with fixed size constants
// to the file.
void
Output_merge_data::do_write(Output_file* of)
{
of->write(this->offset(), this->p_, this->len_);
}
// Write the data to a buffer.
void
Output_merge_data::do_write_to_buffer(unsigned char* buffer)
{
memcpy(buffer, this->p_, this->len_);
}
// Print merge stats to stderr.
void
Output_merge_data::do_print_merge_stats(const char* section_name)
{
fprintf(stderr,
_("%s: %s merged constants size: %lu; input: %zu; output: %zu\n"),
program_name, section_name,
static_cast<unsigned long>(this->entsize()),
this->input_count_, this->hashtable_.size());
}
// Class Output_merge_string.
// Add an input section to a merged string section.
template<typename Char_type>
bool
Output_merge_string<Char_type>::do_add_input_section(Relobj* object,
unsigned int shndx)
{
section_size_type sec_len;
bool is_new;
uint64_t addralign = this->addralign();
const unsigned char* pdata = object->decompressed_section_contents(shndx,
&sec_len,
&is_new,
&addralign);
const Char_type* p = reinterpret_cast<const Char_type*>(pdata);
const Char_type* pend = p + sec_len / sizeof(Char_type);
const Char_type* pend0 = pend;
if (sec_len % sizeof(Char_type) != 0)
{
object->error(_("mergeable string section length not multiple of "
"character size"));
if (is_new)
delete[] pdata;
return false;
}
if (pend[-1] != 0)
{
gold_warning(_("%s: last entry in mergeable string section '%s' "
"not null terminated"),
object->name().c_str(),
object->section_name(shndx).c_str());
// Find the end of the last NULL-terminated string in the buffer.
while (pend0 > p && pend0[-1] != 0)
--pend0;
}
Merged_strings_list* merged_strings_list =
new Merged_strings_list(object, shndx);
this->merged_strings_lists_.push_back(merged_strings_list);
Merged_strings& merged_strings = merged_strings_list->merged_strings;
// Count the number of non-null strings in the section and size the list.
size_t count = 0;
const Char_type* pt = p;
while (pt < pend0)
{
size_t len = string_length(pt);
if (len != 0)
++count;
pt += len + 1;
}
if (pend0 < pend)
++count;
merged_strings.reserve(count + 1);
// The index I is in bytes, not characters.
section_size_type i = 0;
// We assume here that the beginning of the section is correctly
// aligned, so each string within the section must retain the same
// modulo.
uintptr_t init_align_modulo = (reinterpret_cast<uintptr_t>(pdata)
& (addralign - 1));
bool has_misaligned_strings = false;
while (p < pend)
{
size_t len = p < pend0 ? string_length(p) : pend - p;
// Within merge input section each string must be aligned.
if (len != 0
&& ((reinterpret_cast<uintptr_t>(p) & (addralign - 1))
!= init_align_modulo))
has_misaligned_strings = true;
Stringpool::Key key;
this->stringpool_.add_with_length(p, len, true, &key);
merged_strings.push_back(Merged_string(i, key));
p += len + 1;
i += (len + 1) * sizeof(Char_type);
}
// Record the last offset in the input section so that we can
// compute the length of the last string.
merged_strings.push_back(Merged_string(i, 0));
this->input_count_ += count;
this->input_size_ += i;
if (has_misaligned_strings)
gold_warning(_("%s: section %s contains incorrectly aligned strings;"
" the alignment of those strings won't be preserved"),
object->name().c_str(),
object->section_name(shndx).c_str());
// For script processing, we keep the input sections.
if (this->keeps_input_sections())
record_input_section(object, shndx);
if (is_new)
delete[] pdata;
return true;
}
// Finalize the mappings from the input sections to the output
// section, and return the final data size.
template<typename Char_type>
section_size_type
Output_merge_string<Char_type>::finalize_merged_data()
{
this->stringpool_.set_string_offsets();
for (typename Merged_strings_lists::const_iterator l =
this->merged_strings_lists_.begin();
l != this->merged_strings_lists_.end();
++l)
{
section_offset_type last_input_offset = 0;
section_offset_type last_output_offset = 0;
Relobj *object = (*l)->object;
Object_merge_map* merge_map = object->get_or_create_merge_map();
Object_merge_map::Input_merge_map* input_merge_map =
merge_map->get_or_make_input_merge_map(this, (*l)->shndx);
for (typename Merged_strings::const_iterator p =
(*l)->merged_strings.begin();
p != (*l)->merged_strings.end();
++p)
{
section_size_type length = p->offset - last_input_offset;
if (length > 0)
input_merge_map->add_mapping(last_input_offset, length,
last_output_offset);
last_input_offset = p->offset;
if (p->stringpool_key != 0)
last_output_offset =
this->stringpool_.get_offset_from_key(p->stringpool_key);
}
delete *l;
}
// Save some memory. This also ensures that this function will work
// if called twice, as may happen if Layout::set_segment_offsets
// finds a better alignment.
this->merged_strings_lists_.clear();
return this->stringpool_.get_strtab_size();
}
template<typename Char_type>
void
Output_merge_string<Char_type>::set_final_data_size()
{
const off_t final_data_size = this->finalize_merged_data();
this->set_data_size(final_data_size);
}
// Write out a merged string section.
template<typename Char_type>
void
Output_merge_string<Char_type>::do_write(Output_file* of)
{
this->stringpool_.write(of, this->offset());
}
// Write a merged string section to a buffer.
template<typename Char_type>
void
Output_merge_string<Char_type>::do_write_to_buffer(unsigned char* buffer)
{
this->stringpool_.write_to_buffer(buffer, this->data_size());
}
// Return the name of the types of string to use with
// do_print_merge_stats.
template<typename Char_type>
const char*
Output_merge_string<Char_type>::string_name()
{
gold_unreachable();
return NULL;
}
template<>
const char*
Output_merge_string<char>::string_name()
{
return "strings";
}
template<>
const char*
Output_merge_string<uint16_t>::string_name()
{
return "16-bit strings";
}
template<>
const char*
Output_merge_string<uint32_t>::string_name()
{
return "32-bit strings";
}
// Print merge stats to stderr.
template<typename Char_type>
void
Output_merge_string<Char_type>::do_print_merge_stats(const char* section_name)
{
char buf[200];
snprintf(buf, sizeof buf, "%s merged %s", section_name, this->string_name());
fprintf(stderr, _("%s: %s input bytes: %zu\n"),
program_name, buf, this->input_size_);
fprintf(stderr, _("%s: %s input strings: %zu\n"),
program_name, buf, this->input_count_);
this->stringpool_.print_stats(buf);
}
// Instantiate the templates we need.
template
class Output_merge_string<char>;
template
class Output_merge_string<char16_t>;
template
class Output_merge_string<char32_t>;
#if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
template
void
Object_merge_map::initialize_input_to_output_map<32>(
unsigned int shndx,
elfcpp::Elf_types<32>::Elf_Addr starting_address,
Unordered_map<section_offset_type, elfcpp::Elf_types<32>::Elf_Addr>*);
#endif
#if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
template
void
Object_merge_map::initialize_input_to_output_map<64>(
unsigned int shndx,
elfcpp::Elf_types<64>::Elf_Addr starting_address,
Unordered_map<section_offset_type, elfcpp::Elf_types<64>::Elf_Addr>*);
#endif
} // End namespace gold.