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// reduced_debug_output.cc -- output reduced debugging information to save space
// Copyright (C) 2008-2024 Free Software Foundation, Inc.
// Written by Caleb Howe <cshowe@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 "parameters.h"
#include "options.h"
#include "dwarf.h"
#include "dwarf_reader.h"
#include "reduced_debug_output.h"
#include "int_encoding.h"
#include <vector>
namespace gold
{
// Given a pointer to the beginning of a die and the beginning of the associated
// abbreviation fills in die_end with the end of the information entry. If
// successful returns true. Get_die_end also takes a pointer to the end of the
// buffer containing the die. If die_end would be beyond the end of the
// buffer, or if an unsupported dwarf form is encountered returns false.
bool
Output_reduced_debug_info_section::get_die_end(
unsigned char* die, unsigned char* abbrev, unsigned char** die_end,
unsigned char* buffer_end, int address_size, bool is64)
{
size_t LEB_size;
uint64_t LEB_decoded;
for(;;)
{
uint64_t attribute = read_unsigned_LEB_128(abbrev, &LEB_size);
abbrev += LEB_size;
elfcpp::DW_FORM form =
static_cast<elfcpp::DW_FORM>(read_unsigned_LEB_128(abbrev,
&LEB_size));
abbrev += LEB_size;
if (!(attribute || form))
break;
if (die >= buffer_end)
return false;
switch(form)
{
case elfcpp::DW_FORM_flag_present:
break;
case elfcpp::DW_FORM_strp:
case elfcpp::DW_FORM_sec_offset:
die += is64 ? 8 : 4;
break;
case elfcpp::DW_FORM_addr:
case elfcpp::DW_FORM_ref_addr:
die += address_size;
break;
case elfcpp::DW_FORM_block1:
die += *die;
die += 1;
break;
case elfcpp::DW_FORM_block2:
{
uint16_t block_size;
block_size = read_from_pointer<16>(&die);
die += block_size;
break;
}
case elfcpp::DW_FORM_block4:
{
uint32_t block_size;
block_size = read_from_pointer<32>(&die);
die += block_size;
break;
}
case elfcpp::DW_FORM_block:
case elfcpp::DW_FORM_exprloc:
LEB_decoded = read_unsigned_LEB_128(die, &LEB_size);
die += (LEB_decoded + LEB_size);
break;
case elfcpp::DW_FORM_data1:
case elfcpp::DW_FORM_ref1:
case elfcpp::DW_FORM_flag:
die += 1;
break;
case elfcpp::DW_FORM_data2:
case elfcpp::DW_FORM_ref2:
die += 2;
break;
case elfcpp::DW_FORM_data4:
case elfcpp::DW_FORM_ref4:
die += 4;
break;
case elfcpp::DW_FORM_data8:
case elfcpp::DW_FORM_ref8:
case elfcpp::DW_FORM_ref_sig8:
die += 8;
break;
case elfcpp::DW_FORM_ref_udata:
case elfcpp::DW_FORM_udata:
read_unsigned_LEB_128(die, &LEB_size);
die += LEB_size;
break;
case elfcpp::DW_FORM_sdata:
read_signed_LEB_128(die, &LEB_size);
die += LEB_size;
break;
case elfcpp::DW_FORM_string:
{
size_t length = strlen(reinterpret_cast<char*>(die));
die += length + 1;
break;
}
case elfcpp::DW_FORM_indirect:
case elfcpp::DW_FORM_GNU_addr_index:
case elfcpp::DW_FORM_GNU_str_index:
default:
return false;
}
}
*die_end = die;
return true;
}
void
Output_reduced_debug_abbrev_section::set_final_data_size()
{
if (this->sized_ || this->failed_)
return;
uint64_t abbrev_number;
size_t LEB_size;
unsigned char* abbrev_data = this->postprocessing_buffer();
unsigned char* abbrev_end = this->postprocessing_buffer() +
this->postprocessing_buffer_size();
this->write_to_postprocessing_buffer();
while(abbrev_data < abbrev_end)
{
uint64_t abbrev_offset = abbrev_data - this->postprocessing_buffer();
while((abbrev_number = read_unsigned_LEB_128(abbrev_data, &LEB_size)))
{
if (abbrev_data >= abbrev_end)
{
failed("Debug abbreviations extend beyond .debug_abbrev "
"section; failed to reduce debug abbreviations");
return;
}
abbrev_data += LEB_size;
// Together with the abbreviation number these fields make up
// the header for each abbreviation.
uint64_t abbrev_type = read_unsigned_LEB_128(abbrev_data, &LEB_size);
abbrev_data += LEB_size;
// This would ordinarily be the has_children field of the
// abbreviation. But it's going to be false after reducing the
// information, so there's no point in storing it.
abbrev_data++;
// Read to the end of the current abbreviation.
// This is indicated by two zero unsigned LEBs in a row. We don't
// need to parse the data yet, so we just scan through the data
// looking for two consecutive 0 bytes indicating the end of the
// abbreviation.
unsigned char* current_abbrev;
for (current_abbrev = abbrev_data;
current_abbrev[0] || current_abbrev[1];
current_abbrev++)
{
if (current_abbrev >= abbrev_end)
{
this->failed(_("Debug abbreviations extend beyond "
".debug_abbrev section; failed to reduce "
"debug abbreviations"));
return;
}
}
// Account for the two nulls and advance to the start of the
// next abbreviation.
current_abbrev += 2;
// We're eliminating every entry except for compile units, so we
// only need to store abbreviations that describe them
if (abbrev_type == elfcpp::DW_TAG_compile_unit)
{
write_unsigned_LEB_128(&this->data_, ++this->abbrev_count_);
write_unsigned_LEB_128(&this->data_, abbrev_type);
// has_children is false for all entries
this->data_.push_back(0);
this->abbrev_mapping_[std::make_pair(abbrev_offset,
abbrev_number)] =
std::make_pair(abbrev_count_, this->data_.size());
this->data_.insert(this->data_.end(), abbrev_data,
current_abbrev);
}
abbrev_data = current_abbrev;
}
gold_assert(LEB_size == 1);
abbrev_data += LEB_size;
}
// Null terminate the list of abbreviations
this->data_.push_back(0);
this->set_data_size(data_.size());
this->sized_ = true;
}
void
Output_reduced_debug_abbrev_section::do_write(Output_file* of)
{
off_t offset = this->offset();
off_t data_size = this->data_size();
unsigned char* view = of->get_output_view(offset, data_size);
if (this->failed_)
memcpy(view, this->postprocessing_buffer(),
this->postprocessing_buffer_size());
else
memcpy(view, &this->data_.front(), data_size);
of->write_output_view(offset, data_size, view);
}
// Locates the abbreviation with abbreviation_number abbrev_number in the
// abbreviation table at offset abbrev_offset. abbrev_number is updated with
// its new abbreviation number and a pointer to the beginning of the
// abbreviation is returned.
unsigned char*
Output_reduced_debug_abbrev_section::get_new_abbrev(
uint64_t* abbrev_number, uint64_t abbrev_offset)
{
set_final_data_size();
std::pair<uint64_t, uint64_t> abbrev_info =
this->abbrev_mapping_[std::make_pair(abbrev_offset, *abbrev_number)];
*abbrev_number = abbrev_info.first;
return &this->data_[abbrev_info.second];
}
void Output_reduced_debug_info_section::set_final_data_size()
{
if (this->failed_)
return;
unsigned char* debug_info = this->postprocessing_buffer();
unsigned char* debug_info_end = (this->postprocessing_buffer()
+ this->postprocessing_buffer_size());
unsigned char* next_compile_unit;
this->write_to_postprocessing_buffer();
while (debug_info < debug_info_end)
{
uint32_t compile_unit_start = read_from_pointer<32>(&debug_info);
// The first 4 bytes of each compile unit determine whether or
// not we're using dwarf32 or dwarf64. This is not necessarily
// related to whether the binary is 32 or 64 bits.
if (compile_unit_start == 0xFFFFFFFF)
{
// Technically the size can be up to 96 bits. Rather than handle
// 96/128 bit integers we just truncate the size at 64 bits.
if (0 != read_from_pointer<32>(&debug_info))
{
this->failed(_("Extremely large compile unit in debug info; "
"failed to reduce debug info"));
return;
}
const int dwarf64_header_size = sizeof(uint64_t) + sizeof(uint16_t) +
sizeof(uint64_t) + sizeof(uint8_t);
if (debug_info + dwarf64_header_size >= debug_info_end)
{
this->failed(_("Debug info extends beyond .debug_info section;"
"failed to reduce debug info"));
return;
}
uint64_t compile_unit_size = read_from_pointer<64>(&debug_info);
next_compile_unit = debug_info + compile_unit_size;
uint16_t version = read_from_pointer<16>(&debug_info);
uint64_t abbrev_offset = read_from_pointer<64>(&debug_info);
uint8_t address_size = read_from_pointer<8>(&debug_info);
size_t LEB_size;
uint64_t abbreviation_number = read_unsigned_LEB_128(debug_info,
&LEB_size);
debug_info += LEB_size;
unsigned char* die_abbrev = this->associated_abbrev_->get_new_abbrev(
&abbreviation_number, abbrev_offset);
unsigned char* die_end;
if (!this->get_die_end(debug_info, die_abbrev, &die_end,
debug_info_end, address_size, true))
{
this->failed(_("Invalid DIE in debug info; "
"failed to reduce debug info"));
return;
}
insert_into_vector<32>(&this->data_, 0xFFFFFFFF);
insert_into_vector<32>(&this->data_, 0);
insert_into_vector<64>(
&this->data_,
(11 + get_length_as_unsigned_LEB_128(abbreviation_number)
+ die_end - debug_info));
insert_into_vector<16>(&this->data_, version);
insert_into_vector<64>(&this->data_, 0);
insert_into_vector<8>(&this->data_, address_size);
write_unsigned_LEB_128(&this->data_, abbreviation_number);
this->data_.insert(this->data_.end(), debug_info, die_end);
}
else
{
const int dwarf32_header_size =
sizeof(uint16_t) + sizeof(uint32_t) + sizeof(uint8_t);
if (debug_info + dwarf32_header_size >= debug_info_end)
{
this->failed(_("Debug info extends beyond .debug_info section; "
"failed to reduce debug info"));
return;
}
uint32_t compile_unit_size = compile_unit_start;
next_compile_unit = debug_info + compile_unit_size;
uint16_t version = read_from_pointer<16>(&debug_info);
uint32_t abbrev_offset = read_from_pointer<32>(&debug_info);
uint8_t address_size = read_from_pointer<8>(&debug_info);
size_t LEB_size;
uint64_t abbreviation_number = read_unsigned_LEB_128(debug_info,
&LEB_size);
debug_info += LEB_size;
unsigned char* die_abbrev = this->associated_abbrev_->get_new_abbrev(
&abbreviation_number, abbrev_offset);
unsigned char* die_end;
if (!this->get_die_end(debug_info, die_abbrev, &die_end,
debug_info_end, address_size, false))
{
this->failed(_("Invalid DIE in debug info; "
"failed to reduce debug info"));
return;
}
insert_into_vector<32>(
&this->data_,
(7 + get_length_as_unsigned_LEB_128(abbreviation_number)
+ die_end - debug_info));
insert_into_vector<16>(&this->data_, version);
insert_into_vector<32>(&this->data_, 0);
insert_into_vector<8>(&this->data_, address_size);
write_unsigned_LEB_128(&this->data_, abbreviation_number);
this->data_.insert(this->data_.end(), debug_info, die_end);
}
debug_info = next_compile_unit;
}
this->set_data_size(data_.size());
}
void Output_reduced_debug_info_section::do_write(Output_file* of)
{
off_t offset = this->offset();
off_t data_size = this->data_size();
unsigned char* view = of->get_output_view(offset, data_size);
if (this->failed_)
memcpy(view, this->postprocessing_buffer(),
this->postprocessing_buffer_size());
else
memcpy(view, &this->data_.front(), data_size);
of->write_output_view(offset, data_size, view);
}
} // End namespace gold.