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binutils-gdb/gold/layout.cc
Ian Lance Taylor a445fddf82 Fully implement the SECTIONS clause.
2008-02-04 05:43:05 +00:00

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// layout.cc -- lay out output file sections for gold
// Copyright 2006, 2007, 2008 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 <cstring>
#include <algorithm>
#include <iostream>
#include <utility>
#include "parameters.h"
#include "options.h"
#include "script.h"
#include "script-sections.h"
#include "output.h"
#include "symtab.h"
#include "dynobj.h"
#include "ehframe.h"
#include "compressed_output.h"
#include "layout.h"
namespace gold
{
// Layout_task_runner methods.
// Lay out the sections. This is called after all the input objects
// have been read.
void
Layout_task_runner::run(Workqueue* workqueue, const Task* task)
{
off_t file_size = this->layout_->finalize(this->input_objects_,
this->symtab_,
task);
// Now we know the final size of the output file and we know where
// each piece of information goes.
Output_file* of = new Output_file(parameters->output_file_name());
of->open(file_size);
// Queue up the final set of tasks.
gold::queue_final_tasks(this->options_, this->input_objects_,
this->symtab_, this->layout_, workqueue, of);
}
// Layout methods.
Layout::Layout(const General_options& options, Script_options* script_options)
: options_(options), script_options_(script_options), namepool_(),
sympool_(), dynpool_(), signatures_(),
section_name_map_(), segment_list_(), section_list_(),
unattached_section_list_(), special_output_list_(),
section_headers_(NULL), tls_segment_(NULL), symtab_section_(NULL),
dynsym_section_(NULL), dynamic_section_(NULL), dynamic_data_(NULL),
eh_frame_section_(NULL), output_file_size_(-1),
input_requires_executable_stack_(false),
input_with_gnu_stack_note_(false),
input_without_gnu_stack_note_(false),
has_static_tls_(false),
any_postprocessing_sections_(false)
{
// Make space for more than enough segments for a typical file.
// This is just for efficiency--it's OK if we wind up needing more.
this->segment_list_.reserve(12);
// We expect two unattached Output_data objects: the file header and
// the segment headers.
this->special_output_list_.reserve(2);
}
// Hash a key we use to look up an output section mapping.
size_t
Layout::Hash_key::operator()(const Layout::Key& k) const
{
return k.first + k.second.first + k.second.second;
}
// Return whether PREFIX is a prefix of STR.
static inline bool
is_prefix_of(const char* prefix, const char* str)
{
return strncmp(prefix, str, strlen(prefix)) == 0;
}
// Returns whether the given section is in the list of
// debug-sections-used-by-some-version-of-gdb. Currently,
// we've checked versions of gdb up to and including 6.7.1.
static const char* gdb_sections[] =
{ ".debug_abbrev",
// ".debug_aranges", // not used by gdb as of 6.7.1
".debug_frame",
".debug_info",
".debug_line",
".debug_loc",
".debug_macinfo",
// ".debug_pubnames", // not used by gdb as of 6.7.1
".debug_ranges",
".debug_str",
};
static inline bool
is_gdb_debug_section(const char* str)
{
// We can do this faster: binary search or a hashtable. But why bother?
for (size_t i = 0; i < sizeof(gdb_sections)/sizeof(*gdb_sections); ++i)
if (strcmp(str, gdb_sections[i]) == 0)
return true;
return false;
}
// Whether to include this section in the link.
template<int size, bool big_endian>
bool
Layout::include_section(Sized_relobj<size, big_endian>*, const char* name,
const elfcpp::Shdr<size, big_endian>& shdr)
{
// Some section types are never linked. Some are only linked when
// doing a relocateable link.
switch (shdr.get_sh_type())
{
case elfcpp::SHT_NULL:
case elfcpp::SHT_SYMTAB:
case elfcpp::SHT_DYNSYM:
case elfcpp::SHT_STRTAB:
case elfcpp::SHT_HASH:
case elfcpp::SHT_DYNAMIC:
case elfcpp::SHT_SYMTAB_SHNDX:
return false;
case elfcpp::SHT_RELA:
case elfcpp::SHT_REL:
case elfcpp::SHT_GROUP:
return parameters->output_is_object();
case elfcpp::SHT_PROGBITS:
if (parameters->strip_debug()
&& (shdr.get_sh_flags() & elfcpp::SHF_ALLOC) == 0)
{
// Debugging sections can only be recognized by name.
if (is_prefix_of(".debug", name)
|| is_prefix_of(".gnu.linkonce.wi.", name)
|| is_prefix_of(".line", name)
|| is_prefix_of(".stab", name))
return false;
}
if (parameters->strip_debug_gdb()
&& (shdr.get_sh_flags() & elfcpp::SHF_ALLOC) == 0)
{
// Debugging sections can only be recognized by name.
if (is_prefix_of(".debug", name)
&& !is_gdb_debug_section(name))
return false;
}
return true;
default:
return true;
}
}
// Return an output section named NAME, or NULL if there is none.
Output_section*
Layout::find_output_section(const char* name) const
{
for (Section_list::const_iterator p = this->section_list_.begin();
p != this->section_list_.end();
++p)
if (strcmp((*p)->name(), name) == 0)
return *p;
return NULL;
}
// Return an output segment of type TYPE, with segment flags SET set
// and segment flags CLEAR clear. Return NULL if there is none.
Output_segment*
Layout::find_output_segment(elfcpp::PT type, elfcpp::Elf_Word set,
elfcpp::Elf_Word clear) const
{
for (Segment_list::const_iterator p = this->segment_list_.begin();
p != this->segment_list_.end();
++p)
if (static_cast<elfcpp::PT>((*p)->type()) == type
&& ((*p)->flags() & set) == set
&& ((*p)->flags() & clear) == 0)
return *p;
return NULL;
}
// Return the output section to use for section NAME with type TYPE
// and section flags FLAGS. NAME must be canonicalized in the string
// pool, and NAME_KEY is the key.
Output_section*
Layout::get_output_section(const char* name, Stringpool::Key name_key,
elfcpp::Elf_Word type, elfcpp::Elf_Xword flags)
{
const Key key(name_key, std::make_pair(type, flags));
const std::pair<Key, Output_section*> v(key, NULL);
std::pair<Section_name_map::iterator, bool> ins(
this->section_name_map_.insert(v));
if (!ins.second)
return ins.first->second;
else
{
// This is the first time we've seen this name/type/flags
// combination.
Output_section* os = this->make_output_section(name, type, flags);
ins.first->second = os;
return os;
}
}
// Pick the output section to use for section NAME, in input file
// RELOBJ, with type TYPE and flags FLAGS. RELOBJ may be NULL for a
// linker created section. ADJUST_NAME is true if we should apply the
// standard name mappings in Layout::output_section_name. This will
// return NULL if the input section should be discarded.
Output_section*
Layout::choose_output_section(const Relobj* relobj, const char* name,
elfcpp::Elf_Word type, elfcpp::Elf_Xword flags,
bool adjust_name)
{
// We should ignore some flags. FIXME: This will need some
// adjustment for ld -r.
flags &= ~ (elfcpp::SHF_INFO_LINK
| elfcpp::SHF_LINK_ORDER
| elfcpp::SHF_GROUP
| elfcpp::SHF_MERGE
| elfcpp::SHF_STRINGS);
if (this->script_options_->saw_sections_clause())
{
// We are using a SECTIONS clause, so the output section is
// chosen based only on the name.
Script_sections* ss = this->script_options_->script_sections();
const char* file_name = relobj == NULL ? NULL : relobj->name().c_str();
Output_section** output_section_slot;
name = ss->output_section_name(file_name, name, &output_section_slot);
if (name == NULL)
{
// The SECTIONS clause says to discard this input section.
return NULL;
}
// If this is an orphan section--one not mentioned in the linker
// script--then OUTPUT_SECTION_SLOT will be NULL, and we do the
// default processing below.
if (output_section_slot != NULL)
{
if (*output_section_slot != NULL)
return *output_section_slot;
// We don't put sections found in the linker script into
// SECTION_NAME_MAP_. That keeps us from getting confused
// if an orphan section is mapped to a section with the same
// name as one in the linker script.
name = this->namepool_.add(name, false, NULL);
Output_section* os = this->make_output_section(name, type, flags);
os->set_found_in_sections_clause();
*output_section_slot = os;
return os;
}
}
// FIXME: Handle SHF_OS_NONCONFORMING somewhere.
// Turn NAME from the name of the input section into the name of the
// output section.
size_t len = strlen(name);
if (adjust_name && !parameters->output_is_object())
name = Layout::output_section_name(name, &len);
Stringpool::Key name_key;
name = this->namepool_.add_with_length(name, len, true, &name_key);
// Find or make the output section. The output section is selected
// based on the section name, type, and flags.
return this->get_output_section(name, name_key, type, flags);
}
// Return the output section to use for input section SHNDX, with name
// NAME, with header HEADER, from object OBJECT. RELOC_SHNDX is the
// index of a relocation section which applies to this section, or 0
// if none, or -1U if more than one. RELOC_TYPE is the type of the
// relocation section if there is one. Set *OFF to the offset of this
// input section without the output section. Return NULL if the
// section should be discarded. Set *OFF to -1 if the section
// contents should not be written directly to the output file, but
// will instead receive special handling.
template<int size, bool big_endian>
Output_section*
Layout::layout(Sized_relobj<size, big_endian>* object, unsigned int shndx,
const char* name, const elfcpp::Shdr<size, big_endian>& shdr,
unsigned int reloc_shndx, unsigned int, off_t* off)
{
if (!this->include_section(object, name, shdr))
return NULL;
Output_section* os = this->choose_output_section(object,
name,
shdr.get_sh_type(),
shdr.get_sh_flags(),
true);
if (os == NULL)
return NULL;
// FIXME: Handle SHF_LINK_ORDER somewhere.
*off = os->add_input_section(object, shndx, name, shdr, reloc_shndx,
this->script_options_->saw_sections_clause());
return os;
}
// Special GNU handling of sections name .eh_frame. They will
// normally hold exception frame data as defined by the C++ ABI
// (http://codesourcery.com/cxx-abi/).
template<int size, bool big_endian>
Output_section*
Layout::layout_eh_frame(Sized_relobj<size, big_endian>* object,
const unsigned char* symbols,
off_t symbols_size,
const unsigned char* symbol_names,
off_t symbol_names_size,
unsigned int shndx,
const elfcpp::Shdr<size, big_endian>& shdr,
unsigned int reloc_shndx, unsigned int reloc_type,
off_t* off)
{
gold_assert(shdr.get_sh_type() == elfcpp::SHT_PROGBITS);
gold_assert(shdr.get_sh_flags() == elfcpp::SHF_ALLOC);
const char* const name = ".eh_frame";
Output_section* os = this->choose_output_section(object,
name,
elfcpp::SHT_PROGBITS,
elfcpp::SHF_ALLOC,
false);
if (os == NULL)
return NULL;
if (this->eh_frame_section_ == NULL)
{
this->eh_frame_section_ = os;
this->eh_frame_data_ = new Eh_frame();
os->add_output_section_data(this->eh_frame_data_);
if (this->options_.create_eh_frame_hdr())
{
Output_section* hdr_os =
this->choose_output_section(NULL,
".eh_frame_hdr",
elfcpp::SHT_PROGBITS,
elfcpp::SHF_ALLOC,
false);
if (hdr_os != NULL)
{
Eh_frame_hdr* hdr_posd = new Eh_frame_hdr(os,
this->eh_frame_data_);
hdr_os->add_output_section_data(hdr_posd);
hdr_os->set_after_input_sections();
Output_segment* hdr_oseg =
new Output_segment(elfcpp::PT_GNU_EH_FRAME, elfcpp::PF_R);
this->segment_list_.push_back(hdr_oseg);
hdr_oseg->add_output_section(hdr_os, elfcpp::PF_R);
this->eh_frame_data_->set_eh_frame_hdr(hdr_posd);
}
}
}
gold_assert(this->eh_frame_section_ == os);
if (this->eh_frame_data_->add_ehframe_input_section(object,
symbols,
symbols_size,
symbol_names,
symbol_names_size,
shndx,
reloc_shndx,
reloc_type))
*off = -1;
else
{
// We couldn't handle this .eh_frame section for some reason.
// Add it as a normal section.
bool saw_sections_clause = this->script_options_->saw_sections_clause();
*off = os->add_input_section(object, shndx, name, shdr, reloc_shndx,
saw_sections_clause);
}
return os;
}
// Add POSD to an output section using NAME, TYPE, and FLAGS.
void
Layout::add_output_section_data(const char* name, elfcpp::Elf_Word type,
elfcpp::Elf_Xword flags,
Output_section_data* posd)
{
Output_section* os = this->choose_output_section(NULL, name, type, flags,
false);
if (os != NULL)
os->add_output_section_data(posd);
}
// Map section flags to segment flags.
elfcpp::Elf_Word
Layout::section_flags_to_segment(elfcpp::Elf_Xword flags)
{
elfcpp::Elf_Word ret = elfcpp::PF_R;
if ((flags & elfcpp::SHF_WRITE) != 0)
ret |= elfcpp::PF_W;
if ((flags & elfcpp::SHF_EXECINSTR) != 0)
ret |= elfcpp::PF_X;
return ret;
}
// Sometimes we compress sections. This is typically done for
// sections that are not part of normal program execution (such as
// .debug_* sections), and where the readers of these sections know
// how to deal with compressed sections. (To make it easier for them,
// we will rename the ouput section in such cases from .foo to
// .foo.zlib.nnnn, where nnnn is the uncompressed size.) This routine
// doesn't say for certain whether we'll compress -- it depends on
// commandline options as well -- just whether this section is a
// candidate for compression.
static bool
is_compressible_debug_section(const char* secname)
{
return (strncmp(secname, ".debug", sizeof(".debug") - 1) == 0);
}
// Make a new Output_section, and attach it to segments as
// appropriate.
Output_section*
Layout::make_output_section(const char* name, elfcpp::Elf_Word type,
elfcpp::Elf_Xword flags)
{
Output_section* os;
if ((flags & elfcpp::SHF_ALLOC) == 0
&& this->options_.compress_debug_sections()
&& is_compressible_debug_section(name))
os = new Output_compressed_section(&this->options_, name, type, flags);
else
os = new Output_section(name, type, flags);
this->section_list_.push_back(os);
if ((flags & elfcpp::SHF_ALLOC) == 0)
this->unattached_section_list_.push_back(os);
else
{
// If we have a SECTIONS clause, we can't handle the attachment
// to segments until after we've seen all the sections.
if (this->script_options_->saw_sections_clause())
return os;
// This output section goes into a PT_LOAD segment.
elfcpp::Elf_Word seg_flags = Layout::section_flags_to_segment(flags);
// The only thing we really care about for PT_LOAD segments is
// whether or not they are writable, so that is how we search
// for them. People who need segments sorted on some other
// basis will have to wait until we implement a mechanism for
// them to describe the segments they want.
Segment_list::const_iterator p;
for (p = this->segment_list_.begin();
p != this->segment_list_.end();
++p)
{
if ((*p)->type() == elfcpp::PT_LOAD
&& ((*p)->flags() & elfcpp::PF_W) == (seg_flags & elfcpp::PF_W))
{
(*p)->add_output_section(os, seg_flags);
break;
}
}
if (p == this->segment_list_.end())
{
Output_segment* oseg = new Output_segment(elfcpp::PT_LOAD,
seg_flags);
this->segment_list_.push_back(oseg);
oseg->add_output_section(os, seg_flags);
}
// If we see a loadable SHT_NOTE section, we create a PT_NOTE
// segment.
if (type == elfcpp::SHT_NOTE)
{
// See if we already have an equivalent PT_NOTE segment.
for (p = this->segment_list_.begin();
p != segment_list_.end();
++p)
{
if ((*p)->type() == elfcpp::PT_NOTE
&& (((*p)->flags() & elfcpp::PF_W)
== (seg_flags & elfcpp::PF_W)))
{
(*p)->add_output_section(os, seg_flags);
break;
}
}
if (p == this->segment_list_.end())
{
Output_segment* oseg = new Output_segment(elfcpp::PT_NOTE,
seg_flags);
this->segment_list_.push_back(oseg);
oseg->add_output_section(os, seg_flags);
}
}
// If we see a loadable SHF_TLS section, we create a PT_TLS
// segment. There can only be one such segment.
if ((flags & elfcpp::SHF_TLS) != 0)
{
if (this->tls_segment_ == NULL)
{
this->tls_segment_ = new Output_segment(elfcpp::PT_TLS,
seg_flags);
this->segment_list_.push_back(this->tls_segment_);
}
this->tls_segment_->add_output_section(os, seg_flags);
}
}
return os;
}
// Handle the .note.GNU-stack section at layout time. SEEN_GNU_STACK
// is whether we saw a .note.GNU-stack section in the object file.
// GNU_STACK_FLAGS is the section flags. The flags give the
// protection required for stack memory. We record this in an
// executable as a PT_GNU_STACK segment. If an object file does not
// have a .note.GNU-stack segment, we must assume that it is an old
// object. On some targets that will force an executable stack.
void
Layout::layout_gnu_stack(bool seen_gnu_stack, uint64_t gnu_stack_flags)
{
if (!seen_gnu_stack)
this->input_without_gnu_stack_note_ = true;
else
{
this->input_with_gnu_stack_note_ = true;
if ((gnu_stack_flags & elfcpp::SHF_EXECINSTR) != 0)
this->input_requires_executable_stack_ = true;
}
}
// Create the dynamic sections which are needed before we read the
// relocs.
void
Layout::create_initial_dynamic_sections(Symbol_table* symtab)
{
if (parameters->doing_static_link())
return;
const char* dynamic_name = this->namepool_.add(".dynamic", false, NULL);
this->dynamic_section_ = this->make_output_section(dynamic_name,
elfcpp::SHT_DYNAMIC,
(elfcpp::SHF_ALLOC
| elfcpp::SHF_WRITE));
symtab->define_in_output_data("_DYNAMIC", NULL, this->dynamic_section_, 0, 0,
elfcpp::STT_OBJECT, elfcpp::STB_LOCAL,
elfcpp::STV_HIDDEN, 0, false, false);
this->dynamic_data_ = new Output_data_dynamic(&this->dynpool_);
this->dynamic_section_->add_output_section_data(this->dynamic_data_);
}
// For each output section whose name can be represented as C symbol,
// define __start and __stop symbols for the section. This is a GNU
// extension.
void
Layout::define_section_symbols(Symbol_table* symtab)
{
for (Section_list::const_iterator p = this->section_list_.begin();
p != this->section_list_.end();
++p)
{
const char* const name = (*p)->name();
if (name[strspn(name,
("0123456789"
"ABCDEFGHIJKLMNOPWRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"_"))]
== '\0')
{
const std::string name_string(name);
const std::string start_name("__start_" + name_string);
const std::string stop_name("__stop_" + name_string);
symtab->define_in_output_data(start_name.c_str(),
NULL, // version
*p,
0, // value
0, // symsize
elfcpp::STT_NOTYPE,
elfcpp::STB_GLOBAL,
elfcpp::STV_DEFAULT,
0, // nonvis
false, // offset_is_from_end
true); // only_if_ref
symtab->define_in_output_data(stop_name.c_str(),
NULL, // version
*p,
0, // value
0, // symsize
elfcpp::STT_NOTYPE,
elfcpp::STB_GLOBAL,
elfcpp::STV_DEFAULT,
0, // nonvis
true, // offset_is_from_end
true); // only_if_ref
}
}
}
// Find the first read-only PT_LOAD segment, creating one if
// necessary.
Output_segment*
Layout::find_first_load_seg()
{
for (Segment_list::const_iterator p = this->segment_list_.begin();
p != this->segment_list_.end();
++p)
{
if ((*p)->type() == elfcpp::PT_LOAD
&& ((*p)->flags() & elfcpp::PF_R) != 0
&& ((*p)->flags() & elfcpp::PF_W) == 0)
return *p;
}
Output_segment* load_seg = new Output_segment(elfcpp::PT_LOAD, elfcpp::PF_R);
this->segment_list_.push_back(load_seg);
return load_seg;
}
// Finalize the layout. When this is called, we have created all the
// output sections and all the output segments which are based on
// input sections. We have several things to do, and we have to do
// them in the right order, so that we get the right results correctly
// and efficiently.
// 1) Finalize the list of output segments and create the segment
// table header.
// 2) Finalize the dynamic symbol table and associated sections.
// 3) Determine the final file offset of all the output segments.
// 4) Determine the final file offset of all the SHF_ALLOC output
// sections.
// 5) Create the symbol table sections and the section name table
// section.
// 6) Finalize the symbol table: set symbol values to their final
// value and make a final determination of which symbols are going
// into the output symbol table.
// 7) Create the section table header.
// 8) Determine the final file offset of all the output sections which
// are not SHF_ALLOC, including the section table header.
// 9) Finalize the ELF file header.
// This function returns the size of the output file.
off_t
Layout::finalize(const Input_objects* input_objects, Symbol_table* symtab,
const Task* task)
{
Target* const target = input_objects->target();
target->finalize_sections(this);
this->count_local_symbols(task, input_objects);
this->create_gold_note();
this->create_executable_stack_info(target);
if (!parameters->output_is_object() && !parameters->doing_static_link())
{
// There was a dynamic object in the link. We need to create
// some information for the dynamic linker.
// Create the dynamic symbol table, including the hash table.
Output_section* dynstr;
std::vector<Symbol*> dynamic_symbols;
unsigned int local_dynamic_count;
Versions versions(this->options_, &this->dynpool_);
this->create_dynamic_symtab(input_objects, symtab, &dynstr,
&local_dynamic_count, &dynamic_symbols,
&versions);
// Create the .interp section to hold the name of the
// interpreter, and put it in a PT_INTERP segment.
if (!parameters->output_is_shared())
this->create_interp(target);
// Finish the .dynamic section to hold the dynamic data, and put
// it in a PT_DYNAMIC segment.
this->finish_dynamic_section(input_objects, symtab);
// We should have added everything we need to the dynamic string
// table.
this->dynpool_.set_string_offsets();
// Create the version sections. We can't do this until the
// dynamic string table is complete.
this->create_version_sections(&versions, symtab, local_dynamic_count,
dynamic_symbols, dynstr);
}
// If there is a SECTIONS clause, put all the input sections into
// the required order.
Output_segment* load_seg;
if (this->script_options_->saw_sections_clause())
load_seg = this->set_section_addresses_from_script(symtab);
else
load_seg = this->find_first_load_seg();
Output_segment* phdr_seg = NULL;
if (load_seg != NULL
&& !parameters->output_is_object()
&& !parameters->doing_static_link())
{
// Create the PT_PHDR segment which will hold the program
// headers.
phdr_seg = new Output_segment(elfcpp::PT_PHDR, elfcpp::PF_R);
this->segment_list_.push_back(phdr_seg);
}
// Lay out the segment headers.
Output_segment_headers* segment_headers;
segment_headers = new Output_segment_headers(this->segment_list_);
if (load_seg != NULL)
load_seg->add_initial_output_data(segment_headers);
if (phdr_seg != NULL)
phdr_seg->add_initial_output_data(segment_headers);
// Lay out the file header.
Output_file_header* file_header;
file_header = new Output_file_header(target, symtab, segment_headers,
this->script_options_->entry());
if (load_seg != NULL)
load_seg->add_initial_output_data(file_header);
this->special_output_list_.push_back(file_header);
this->special_output_list_.push_back(segment_headers);
// We set the output section indexes in set_segment_offsets and
// set_section_indexes.
unsigned int shndx = 1;
// Set the file offsets of all the segments, and all the sections
// they contain.
off_t off = this->set_segment_offsets(target, load_seg, &shndx);
// Set the file offsets of all the non-data sections we've seen so
// far which don't have to wait for the input sections. We need
// this in order to finalize local symbols in non-allocated
// sections.
off = this->set_section_offsets(off, BEFORE_INPUT_SECTIONS_PASS);
// Create the symbol table sections.
this->create_symtab_sections(input_objects, symtab, &off);
if (!parameters->doing_static_link())
this->assign_local_dynsym_offsets(input_objects);
// Process any symbol assignments from a linker script. This must
// be called after the symbol table has been finalized.
this->script_options_->finalize_symbols(symtab, this);
// Create the .shstrtab section.
Output_section* shstrtab_section = this->create_shstrtab();
// Set the file offsets of the rest of the non-data sections which
// don't have to wait for the input sections.
off = this->set_section_offsets(off, BEFORE_INPUT_SECTIONS_PASS);
// Now that all sections have been created, set the section indexes.
shndx = this->set_section_indexes(shndx);
// Create the section table header.
this->create_shdrs(&off);
// If there are no sections which require postprocessing, we can
// handle the section names now, and avoid a resize later.
if (!this->any_postprocessing_sections_)
off = this->set_section_offsets(off,
STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS);
file_header->set_section_info(this->section_headers_, shstrtab_section);
// Now we know exactly where everything goes in the output file
// (except for non-allocated sections which require postprocessing).
Output_data::layout_complete();
this->output_file_size_ = off;
return off;
}
// Create a .note section for an executable or shared library. This
// records the version of gold used to create the binary.
void
Layout::create_gold_note()
{
if (parameters->output_is_object())
return;
// Authorities all agree that the values in a .note field should
// be aligned on 4-byte boundaries for 32-bit binaries. However,
// they differ on what the alignment is for 64-bit binaries.
// The GABI says unambiguously they take 8-byte alignment:
// http://sco.com/developers/gabi/latest/ch5.pheader.html#note_section
// Other documentation says alignment should always be 4 bytes:
// http://www.netbsd.org/docs/kernel/elf-notes.html#note-format
// GNU ld and GNU readelf both support the latter (at least as of
// version 2.16.91), and glibc always generates the latter for
// .note.ABI-tag (as of version 1.6), so that's the one we go with
// here.
#ifdef GABI_FORMAT_FOR_DOTNOTE_SECTION // This is not defined by default.
const int size = parameters->get_size();
#else
const int size = 32;
#endif
// The contents of the .note section.
const char* name = "GNU";
std::string desc(std::string("gold ") + gold::get_version_string());
size_t namesz = strlen(name) + 1;
size_t aligned_namesz = align_address(namesz, size / 8);
size_t descsz = desc.length() + 1;
size_t aligned_descsz = align_address(descsz, size / 8);
const int note_type = 4;
size_t notesz = 3 * (size / 8) + aligned_namesz + aligned_descsz;
unsigned char buffer[128];
gold_assert(sizeof buffer >= notesz);
memset(buffer, 0, notesz);
bool is_big_endian = parameters->is_big_endian();
if (size == 32)
{
if (!is_big_endian)
{
elfcpp::Swap<32, false>::writeval(buffer, namesz);
elfcpp::Swap<32, false>::writeval(buffer + 4, descsz);
elfcpp::Swap<32, false>::writeval(buffer + 8, note_type);
}
else
{
elfcpp::Swap<32, true>::writeval(buffer, namesz);
elfcpp::Swap<32, true>::writeval(buffer + 4, descsz);
elfcpp::Swap<32, true>::writeval(buffer + 8, note_type);
}
}
else if (size == 64)
{
if (!is_big_endian)
{
elfcpp::Swap<64, false>::writeval(buffer, namesz);
elfcpp::Swap<64, false>::writeval(buffer + 8, descsz);
elfcpp::Swap<64, false>::writeval(buffer + 16, note_type);
}
else
{
elfcpp::Swap<64, true>::writeval(buffer, namesz);
elfcpp::Swap<64, true>::writeval(buffer + 8, descsz);
elfcpp::Swap<64, true>::writeval(buffer + 16, note_type);
}
}
else
gold_unreachable();
memcpy(buffer + 3 * (size / 8), name, namesz);
memcpy(buffer + 3 * (size / 8) + aligned_namesz, desc.data(), descsz);
const char* note_name = this->namepool_.add(".note", false, NULL);
Output_section* os = this->make_output_section(note_name,
elfcpp::SHT_NOTE,
0);
Output_section_data* posd = new Output_data_const(buffer, notesz,
size / 8);
os->add_output_section_data(posd);
}
// Record whether the stack should be executable. This can be set
// from the command line using the -z execstack or -z noexecstack
// options. Otherwise, if any input file has a .note.GNU-stack
// section with the SHF_EXECINSTR flag set, the stack should be
// executable. Otherwise, if at least one input file a
// .note.GNU-stack section, and some input file has no .note.GNU-stack
// section, we use the target default for whether the stack should be
// executable. Otherwise, we don't generate a stack note. When
// generating a object file, we create a .note.GNU-stack section with
// the appropriate marking. When generating an executable or shared
// library, we create a PT_GNU_STACK segment.
void
Layout::create_executable_stack_info(const Target* target)
{
bool is_stack_executable;
if (this->options_.is_execstack_set())
is_stack_executable = this->options_.is_stack_executable();
else if (!this->input_with_gnu_stack_note_)
return;
else
{
if (this->input_requires_executable_stack_)
is_stack_executable = true;
else if (this->input_without_gnu_stack_note_)
is_stack_executable = target->is_default_stack_executable();
else
is_stack_executable = false;
}
if (parameters->output_is_object())
{
const char* name = this->namepool_.add(".note.GNU-stack", false, NULL);
elfcpp::Elf_Xword flags = 0;
if (is_stack_executable)
flags |= elfcpp::SHF_EXECINSTR;
this->make_output_section(name, elfcpp::SHT_PROGBITS, flags);
}
else
{
int flags = elfcpp::PF_R | elfcpp::PF_W;
if (is_stack_executable)
flags |= elfcpp::PF_X;
Output_segment* oseg = new Output_segment(elfcpp::PT_GNU_STACK, flags);
this->segment_list_.push_back(oseg);
}
}
// Return whether SEG1 should be before SEG2 in the output file. This
// is based entirely on the segment type and flags. When this is
// called the segment addresses has normally not yet been set.
bool
Layout::segment_precedes(const Output_segment* seg1,
const Output_segment* seg2)
{
elfcpp::Elf_Word type1 = seg1->type();
elfcpp::Elf_Word type2 = seg2->type();
// The single PT_PHDR segment is required to precede any loadable
// segment. We simply make it always first.
if (type1 == elfcpp::PT_PHDR)
{
gold_assert(type2 != elfcpp::PT_PHDR);
return true;
}
if (type2 == elfcpp::PT_PHDR)
return false;
// The single PT_INTERP segment is required to precede any loadable
// segment. We simply make it always second.
if (type1 == elfcpp::PT_INTERP)
{
gold_assert(type2 != elfcpp::PT_INTERP);
return true;
}
if (type2 == elfcpp::PT_INTERP)
return false;
// We then put PT_LOAD segments before any other segments.
if (type1 == elfcpp::PT_LOAD && type2 != elfcpp::PT_LOAD)
return true;
if (type2 == elfcpp::PT_LOAD && type1 != elfcpp::PT_LOAD)
return false;
// We put the PT_TLS segment last, because that is where the dynamic
// linker expects to find it (this is just for efficiency; other
// positions would also work correctly).
if (type1 == elfcpp::PT_TLS && type2 != elfcpp::PT_TLS)
return false;
if (type2 == elfcpp::PT_TLS && type1 != elfcpp::PT_TLS)
return true;
const elfcpp::Elf_Word flags1 = seg1->flags();
const elfcpp::Elf_Word flags2 = seg2->flags();
// The order of non-PT_LOAD segments is unimportant. We simply sort
// by the numeric segment type and flags values. There should not
// be more than one segment with the same type and flags.
if (type1 != elfcpp::PT_LOAD)
{
if (type1 != type2)
return type1 < type2;
gold_assert(flags1 != flags2);
return flags1 < flags2;
}
// If the addresses are set already, sort by load address.
if (seg1->are_addresses_set())
{
if (!seg2->are_addresses_set())
return true;
unsigned int section_count1 = seg1->output_section_count();
unsigned int section_count2 = seg2->output_section_count();
if (section_count1 == 0 && section_count2 > 0)
return true;
if (section_count1 > 0 && section_count2 == 0)
return false;
uint64_t paddr1 = seg1->first_section_load_address();
uint64_t paddr2 = seg2->first_section_load_address();
if (paddr1 != paddr2)
return paddr1 < paddr2;
}
else if (seg2->are_addresses_set())
return false;
// We sort PT_LOAD segments based on the flags. Readonly segments
// come before writable segments. Then executable segments come
// before non-executable segments. Then the unlikely case of a
// non-readable segment comes before the normal case of a readable
// segment. If there are multiple segments with the same type and
// flags, we require that the address be set, and we sort by
// virtual address and then physical address.
if ((flags1 & elfcpp::PF_W) != (flags2 & elfcpp::PF_W))
return (flags1 & elfcpp::PF_W) == 0;
if ((flags1 & elfcpp::PF_X) != (flags2 & elfcpp::PF_X))
return (flags1 & elfcpp::PF_X) != 0;
if ((flags1 & elfcpp::PF_R) != (flags2 & elfcpp::PF_R))
return (flags1 & elfcpp::PF_R) == 0;
// We shouldn't get here--we shouldn't create segments which we
// can't distinguish.
gold_unreachable();
}
// Set the file offsets of all the segments, and all the sections they
// contain. They have all been created. LOAD_SEG must be be laid out
// first. Return the offset of the data to follow.
off_t
Layout::set_segment_offsets(const Target* target, Output_segment* load_seg,
unsigned int *pshndx)
{
// Sort them into the final order.
std::sort(this->segment_list_.begin(), this->segment_list_.end(),
Layout::Compare_segments());
// Find the PT_LOAD segments, and set their addresses and offsets
// and their section's addresses and offsets.
uint64_t addr;
if (this->options_.user_set_text_segment_address())
addr = options_.text_segment_address();
else if (parameters->output_is_shared())
addr = 0;
else
addr = target->default_text_segment_address();
off_t off = 0;
// If LOAD_SEG is NULL, then the file header and segment headers
// will not be loadable. But they still need to be at offset 0 in
// the file. Set their offsets now.
if (load_seg == NULL)
{
for (Data_list::iterator p = this->special_output_list_.begin();
p != this->special_output_list_.end();
++p)
{
off = align_address(off, (*p)->addralign());
(*p)->set_address_and_file_offset(0, off);
off += (*p)->data_size();
}
}
bool was_readonly = false;
for (Segment_list::iterator p = this->segment_list_.begin();
p != this->segment_list_.end();
++p)
{
if ((*p)->type() == elfcpp::PT_LOAD)
{
if (load_seg != NULL && load_seg != *p)
gold_unreachable();
load_seg = NULL;
uint64_t orig_addr = addr;
uint64_t orig_off = off;
uint64_t aligned_addr = 0;
uint64_t abi_pagesize = target->abi_pagesize();
// FIXME: This should depend on the -n and -N options.
(*p)->set_minimum_p_align(target->common_pagesize());
bool are_addresses_set = (*p)->are_addresses_set();
if (are_addresses_set)
{
// When it comes to setting file offsets, we care about
// the physical address.
addr = (*p)->paddr();
// Adjust the file offset to the same address modulo the
// page size.
uint64_t unsigned_off = off;
uint64_t aligned_off = ((unsigned_off & ~(abi_pagesize - 1))
| (addr & (abi_pagesize - 1)));
if (aligned_off < unsigned_off)
aligned_off += abi_pagesize;
off = aligned_off;
}
else
{
// If the last segment was readonly, and this one is
// not, then skip the address forward one page,
// maintaining the same position within the page. This
// lets us store both segments overlapping on a single
// page in the file, but the loader will put them on
// different pages in memory.
addr = align_address(addr, (*p)->maximum_alignment());
aligned_addr = addr;
if (was_readonly && ((*p)->flags() & elfcpp::PF_W) != 0)
{
if ((addr & (abi_pagesize - 1)) != 0)
addr = addr + abi_pagesize;
}
off = orig_off + ((addr - orig_addr) & (abi_pagesize - 1));
}
unsigned int shndx_hold = *pshndx;
uint64_t new_addr = (*p)->set_section_addresses(false, addr, &off,
pshndx);
// Now that we know the size of this segment, we may be able
// to save a page in memory, at the cost of wasting some
// file space, by instead aligning to the start of a new
// page. Here we use the real machine page size rather than
// the ABI mandated page size.
if (!are_addresses_set && aligned_addr != addr)
{
uint64_t common_pagesize = target->common_pagesize();
uint64_t first_off = (common_pagesize
- (aligned_addr
& (common_pagesize - 1)));
uint64_t last_off = new_addr & (common_pagesize - 1);
if (first_off > 0
&& last_off > 0
&& ((aligned_addr & ~ (common_pagesize - 1))
!= (new_addr & ~ (common_pagesize - 1)))
&& first_off + last_off <= common_pagesize)
{
*pshndx = shndx_hold;
addr = align_address(aligned_addr, common_pagesize);
addr = align_address(addr, (*p)->maximum_alignment());
off = orig_off + ((addr - orig_addr) & (abi_pagesize - 1));
new_addr = (*p)->set_section_addresses(true, addr, &off,
pshndx);
}
}
addr = new_addr;
if (((*p)->flags() & elfcpp::PF_W) == 0)
was_readonly = true;
}
}
// Handle the non-PT_LOAD segments, setting their offsets from their
// section's offsets.
for (Segment_list::iterator p = this->segment_list_.begin();
p != this->segment_list_.end();
++p)
{
if ((*p)->type() != elfcpp::PT_LOAD)
(*p)->set_offset();
}
// Set the TLS offsets for each section in the PT_TLS segment.
if (this->tls_segment_ != NULL)
this->tls_segment_->set_tls_offsets();
return off;
}
// Set the file offset of all the sections not associated with a
// segment.
off_t
Layout::set_section_offsets(off_t off, Layout::Section_offset_pass pass)
{
for (Section_list::iterator p = this->unattached_section_list_.begin();
p != this->unattached_section_list_.end();
++p)
{
// The symtab section is handled in create_symtab_sections.
if (*p == this->symtab_section_)
continue;
// If we've already set the data size, don't set it again.
if ((*p)->is_offset_valid() && (*p)->is_data_size_valid())
continue;
if (pass == BEFORE_INPUT_SECTIONS_PASS
&& (*p)->requires_postprocessing())
{
(*p)->create_postprocessing_buffer();
this->any_postprocessing_sections_ = true;
}
if (pass == BEFORE_INPUT_SECTIONS_PASS
&& (*p)->after_input_sections())
continue;
else if (pass == POSTPROCESSING_SECTIONS_PASS
&& (!(*p)->after_input_sections()
|| (*p)->type() == elfcpp::SHT_STRTAB))
continue;
else if (pass == STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS
&& (!(*p)->after_input_sections()
|| (*p)->type() != elfcpp::SHT_STRTAB))
continue;
off = align_address(off, (*p)->addralign());
(*p)->set_file_offset(off);
(*p)->finalize_data_size();
off += (*p)->data_size();
// At this point the name must be set.
if (pass != STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS)
this->namepool_.add((*p)->name(), false, NULL);
}
return off;
}
// Set the section indexes of all the sections not associated with a
// segment.
unsigned int
Layout::set_section_indexes(unsigned int shndx)
{
for (Section_list::iterator p = this->unattached_section_list_.begin();
p != this->unattached_section_list_.end();
++p)
{
(*p)->set_out_shndx(shndx);
++shndx;
}
return shndx;
}
// Set the section addresses according to the linker script. This is
// only called when we see a SECTIONS clause. This returns the
// program segment which should hold the file header and segment
// headers, if any. It will return NULL if they should not be in a
// segment.
Output_segment*
Layout::set_section_addresses_from_script(Symbol_table* symtab)
{
Script_sections* ss = this->script_options_->script_sections();
gold_assert(ss->saw_sections_clause());
// Place each orphaned output section in the script.
for (Section_list::iterator p = this->section_list_.begin();
p != this->section_list_.end();
++p)
{
if (!(*p)->found_in_sections_clause())
ss->place_orphan(*p);
}
return this->script_options_->set_section_addresses(symtab, this);
}
// Count the local symbols in the regular symbol table and the dynamic
// symbol table, and build the respective string pools.
void
Layout::count_local_symbols(const Task* task,
const Input_objects* input_objects)
{
// First, figure out an upper bound on the number of symbols we'll
// be inserting into each pool. This helps us create the pools with
// the right size, to avoid unnecessary hashtable resizing.
unsigned int symbol_count = 0;
for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
p != input_objects->relobj_end();
++p)
symbol_count += (*p)->local_symbol_count();
// Go from "upper bound" to "estimate." We overcount for two
// reasons: we double-count symbols that occur in more than one
// object file, and we count symbols that are dropped from the
// output. Add it all together and assume we overcount by 100%.
symbol_count /= 2;
// We assume all symbols will go into both the sympool and dynpool.
this->sympool_.reserve(symbol_count);
this->dynpool_.reserve(symbol_count);
for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
p != input_objects->relobj_end();
++p)
{
Task_lock_obj<Object> tlo(task, *p);
(*p)->count_local_symbols(&this->sympool_, &this->dynpool_);
}
}
// Create the symbol table sections. Here we also set the final
// values of the symbols. At this point all the loadable sections are
// fully laid out.
void
Layout::create_symtab_sections(const Input_objects* input_objects,
Symbol_table* symtab,
off_t* poff)
{
int symsize;
unsigned int align;
if (parameters->get_size() == 32)
{
symsize = elfcpp::Elf_sizes<32>::sym_size;
align = 4;
}
else if (parameters->get_size() == 64)
{
symsize = elfcpp::Elf_sizes<64>::sym_size;
align = 8;
}
else
gold_unreachable();
off_t off = *poff;
off = align_address(off, align);
off_t startoff = off;
// Save space for the dummy symbol at the start of the section. We
// never bother to write this out--it will just be left as zero.
off += symsize;
unsigned int local_symbol_index = 1;
// Add STT_SECTION symbols for each Output section which needs one.
for (Section_list::iterator p = this->section_list_.begin();
p != this->section_list_.end();
++p)
{
if (!(*p)->needs_symtab_index())
(*p)->set_symtab_index(-1U);
else
{
(*p)->set_symtab_index(local_symbol_index);
++local_symbol_index;
off += symsize;
}
}
for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
p != input_objects->relobj_end();
++p)
{
unsigned int index = (*p)->finalize_local_symbols(local_symbol_index,
off);
off += (index - local_symbol_index) * symsize;
local_symbol_index = index;
}
unsigned int local_symcount = local_symbol_index;
gold_assert(local_symcount * symsize == off - startoff);
off_t dynoff;
size_t dyn_global_index;
size_t dyncount;
if (this->dynsym_section_ == NULL)
{
dynoff = 0;
dyn_global_index = 0;
dyncount = 0;
}
else
{
dyn_global_index = this->dynsym_section_->info();
off_t locsize = dyn_global_index * this->dynsym_section_->entsize();
dynoff = this->dynsym_section_->offset() + locsize;
dyncount = (this->dynsym_section_->data_size() - locsize) / symsize;
gold_assert(static_cast<off_t>(dyncount * symsize)
== this->dynsym_section_->data_size() - locsize);
}
off = symtab->finalize(off, dynoff, dyn_global_index, dyncount,
&this->sympool_, &local_symcount);
if (!parameters->strip_all())
{
this->sympool_.set_string_offsets();
const char* symtab_name = this->namepool_.add(".symtab", false, NULL);
Output_section* osymtab = this->make_output_section(symtab_name,
elfcpp::SHT_SYMTAB,
0);
this->symtab_section_ = osymtab;
Output_section_data* pos = new Output_data_fixed_space(off - startoff,
align);
osymtab->add_output_section_data(pos);
const char* strtab_name = this->namepool_.add(".strtab", false, NULL);
Output_section* ostrtab = this->make_output_section(strtab_name,
elfcpp::SHT_STRTAB,
0);
Output_section_data* pstr = new Output_data_strtab(&this->sympool_);
ostrtab->add_output_section_data(pstr);
osymtab->set_file_offset(startoff);
osymtab->finalize_data_size();
osymtab->set_link_section(ostrtab);
osymtab->set_info(local_symcount);
osymtab->set_entsize(symsize);
*poff = off;
}
}
// Create the .shstrtab section, which holds the names of the
// sections. At the time this is called, we have created all the
// output sections except .shstrtab itself.
Output_section*
Layout::create_shstrtab()
{
// FIXME: We don't need to create a .shstrtab section if we are
// stripping everything.
const char* name = this->namepool_.add(".shstrtab", false, NULL);
Output_section* os = this->make_output_section(name, elfcpp::SHT_STRTAB, 0);
// We can't write out this section until we've set all the section
// names, and we don't set the names of compressed output sections
// until relocations are complete.
os->set_after_input_sections();
Output_section_data* posd = new Output_data_strtab(&this->namepool_);
os->add_output_section_data(posd);
return os;
}
// Create the section headers. SIZE is 32 or 64. OFF is the file
// offset.
void
Layout::create_shdrs(off_t* poff)
{
Output_section_headers* oshdrs;
oshdrs = new Output_section_headers(this,
&this->segment_list_,
&this->unattached_section_list_,
&this->namepool_);
off_t off = align_address(*poff, oshdrs->addralign());
oshdrs->set_address_and_file_offset(0, off);
off += oshdrs->data_size();
*poff = off;
this->section_headers_ = oshdrs;
}
// Create the dynamic symbol table.
void
Layout::create_dynamic_symtab(const Input_objects* input_objects,
Symbol_table* symtab,
Output_section **pdynstr,
unsigned int* plocal_dynamic_count,
std::vector<Symbol*>* pdynamic_symbols,
Versions* pversions)
{
// Count all the symbols in the dynamic symbol table, and set the
// dynamic symbol indexes.
// Skip symbol 0, which is always all zeroes.
unsigned int index = 1;
// Add STT_SECTION symbols for each Output section which needs one.
for (Section_list::iterator p = this->section_list_.begin();
p != this->section_list_.end();
++p)
{
if (!(*p)->needs_dynsym_index())
(*p)->set_dynsym_index(-1U);
else
{
(*p)->set_dynsym_index(index);
++index;
}
}
// Count the local symbols that need to go in the dynamic symbol table,
// and set the dynamic symbol indexes.
for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
p != input_objects->relobj_end();
++p)
{
unsigned int new_index = (*p)->set_local_dynsym_indexes(index);
index = new_index;
}
unsigned int local_symcount = index;
*plocal_dynamic_count = local_symcount;
// FIXME: We have to tell set_dynsym_indexes whether the
// -E/--export-dynamic option was used.
index = symtab->set_dynsym_indexes(index, pdynamic_symbols,
&this->dynpool_, pversions);
int symsize;
unsigned int align;
const int size = parameters->get_size();
if (size == 32)
{
symsize = elfcpp::Elf_sizes<32>::sym_size;
align = 4;
}
else if (size == 64)
{
symsize = elfcpp::Elf_sizes<64>::sym_size;
align = 8;
}
else
gold_unreachable();
// Create the dynamic symbol table section.
const char* dynsym_name = this->namepool_.add(".dynsym", false, NULL);
Output_section* dynsym = this->make_output_section(dynsym_name,
elfcpp::SHT_DYNSYM,
elfcpp::SHF_ALLOC);
Output_section_data* odata = new Output_data_fixed_space(index * symsize,
align);
dynsym->add_output_section_data(odata);
dynsym->set_info(local_symcount);
dynsym->set_entsize(symsize);
dynsym->set_addralign(align);
this->dynsym_section_ = dynsym;
Output_data_dynamic* const odyn = this->dynamic_data_;
odyn->add_section_address(elfcpp::DT_SYMTAB, dynsym);
odyn->add_constant(elfcpp::DT_SYMENT, symsize);
// Create the dynamic string table section.
const char* dynstr_name = this->namepool_.add(".dynstr", false, NULL);
Output_section* dynstr = this->make_output_section(dynstr_name,
elfcpp::SHT_STRTAB,
elfcpp::SHF_ALLOC);
Output_section_data* strdata = new Output_data_strtab(&this->dynpool_);
dynstr->add_output_section_data(strdata);
dynsym->set_link_section(dynstr);
this->dynamic_section_->set_link_section(dynstr);
odyn->add_section_address(elfcpp::DT_STRTAB, dynstr);
odyn->add_section_size(elfcpp::DT_STRSZ, dynstr);
*pdynstr = dynstr;
// Create the hash tables.
// FIXME: We need an option to create a GNU hash table.
unsigned char* phash;
unsigned int hashlen;
Dynobj::create_elf_hash_table(*pdynamic_symbols, local_symcount,
&phash, &hashlen);
const char* hash_name = this->namepool_.add(".hash", false, NULL);
Output_section* hashsec = this->make_output_section(hash_name,
elfcpp::SHT_HASH,
elfcpp::SHF_ALLOC);
Output_section_data* hashdata = new Output_data_const_buffer(phash,
hashlen,
align);
hashsec->add_output_section_data(hashdata);
hashsec->set_link_section(dynsym);
hashsec->set_entsize(4);
odyn->add_section_address(elfcpp::DT_HASH, hashsec);
}
// Assign offsets to each local portion of the dynamic symbol table.
void
Layout::assign_local_dynsym_offsets(const Input_objects* input_objects)
{
Output_section* dynsym = this->dynsym_section_;
gold_assert(dynsym != NULL);
off_t off = dynsym->offset();
// Skip the dummy symbol at the start of the section.
off += dynsym->entsize();
for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
p != input_objects->relobj_end();
++p)
{
unsigned int count = (*p)->set_local_dynsym_offset(off);
off += count * dynsym->entsize();
}
}
// Create the version sections.
void
Layout::create_version_sections(const Versions* versions,
const Symbol_table* symtab,
unsigned int local_symcount,
const std::vector<Symbol*>& dynamic_symbols,
const Output_section* dynstr)
{
if (!versions->any_defs() && !versions->any_needs())
return;
if (parameters->get_size() == 32)
{
if (parameters->is_big_endian())
{
#ifdef HAVE_TARGET_32_BIG
this->sized_create_version_sections
SELECT_SIZE_ENDIAN_NAME(32, true)(
versions, symtab, local_symcount, dynamic_symbols, dynstr
SELECT_SIZE_ENDIAN(32, true));
#else
gold_unreachable();
#endif
}
else
{
#ifdef HAVE_TARGET_32_LITTLE
this->sized_create_version_sections
SELECT_SIZE_ENDIAN_NAME(32, false)(
versions, symtab, local_symcount, dynamic_symbols, dynstr
SELECT_SIZE_ENDIAN(32, false));
#else
gold_unreachable();
#endif
}
}
else if (parameters->get_size() == 64)
{
if (parameters->is_big_endian())
{
#ifdef HAVE_TARGET_64_BIG
this->sized_create_version_sections
SELECT_SIZE_ENDIAN_NAME(64, true)(
versions, symtab, local_symcount, dynamic_symbols, dynstr
SELECT_SIZE_ENDIAN(64, true));
#else
gold_unreachable();
#endif
}
else
{
#ifdef HAVE_TARGET_64_LITTLE
this->sized_create_version_sections
SELECT_SIZE_ENDIAN_NAME(64, false)(
versions, symtab, local_symcount, dynamic_symbols, dynstr
SELECT_SIZE_ENDIAN(64, false));
#else
gold_unreachable();
#endif
}
}
else
gold_unreachable();
}
// Create the version sections, sized version.
template<int size, bool big_endian>
void
Layout::sized_create_version_sections(
const Versions* versions,
const Symbol_table* symtab,
unsigned int local_symcount,
const std::vector<Symbol*>& dynamic_symbols,
const Output_section* dynstr
ACCEPT_SIZE_ENDIAN)
{
const char* vname = this->namepool_.add(".gnu.version", false, NULL);
Output_section* vsec = this->make_output_section(vname,
elfcpp::SHT_GNU_versym,
elfcpp::SHF_ALLOC);
unsigned char* vbuf;
unsigned int vsize;
versions->symbol_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian)(
symtab, &this->dynpool_, local_symcount, dynamic_symbols, &vbuf, &vsize
SELECT_SIZE_ENDIAN(size, big_endian));
Output_section_data* vdata = new Output_data_const_buffer(vbuf, vsize, 2);
vsec->add_output_section_data(vdata);
vsec->set_entsize(2);
vsec->set_link_section(this->dynsym_section_);
Output_data_dynamic* const odyn = this->dynamic_data_;
odyn->add_section_address(elfcpp::DT_VERSYM, vsec);
if (versions->any_defs())
{
const char* vdname = this->namepool_.add(".gnu.version_d", false, NULL);
Output_section *vdsec;
vdsec = this->make_output_section(vdname, elfcpp::SHT_GNU_verdef,
elfcpp::SHF_ALLOC);
unsigned char* vdbuf;
unsigned int vdsize;
unsigned int vdentries;
versions->def_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian)(
&this->dynpool_, &vdbuf, &vdsize, &vdentries
SELECT_SIZE_ENDIAN(size, big_endian));
Output_section_data* vddata = new Output_data_const_buffer(vdbuf,
vdsize,
4);
vdsec->add_output_section_data(vddata);
vdsec->set_link_section(dynstr);
vdsec->set_info(vdentries);
odyn->add_section_address(elfcpp::DT_VERDEF, vdsec);
odyn->add_constant(elfcpp::DT_VERDEFNUM, vdentries);
}
if (versions->any_needs())
{
const char* vnname = this->namepool_.add(".gnu.version_r", false, NULL);
Output_section* vnsec;
vnsec = this->make_output_section(vnname, elfcpp::SHT_GNU_verneed,
elfcpp::SHF_ALLOC);
unsigned char* vnbuf;
unsigned int vnsize;
unsigned int vnentries;
versions->need_section_contents SELECT_SIZE_ENDIAN_NAME(size, big_endian)
(&this->dynpool_, &vnbuf, &vnsize, &vnentries
SELECT_SIZE_ENDIAN(size, big_endian));
Output_section_data* vndata = new Output_data_const_buffer(vnbuf,
vnsize,
4);
vnsec->add_output_section_data(vndata);
vnsec->set_link_section(dynstr);
vnsec->set_info(vnentries);
odyn->add_section_address(elfcpp::DT_VERNEED, vnsec);
odyn->add_constant(elfcpp::DT_VERNEEDNUM, vnentries);
}
}
// Create the .interp section and PT_INTERP segment.
void
Layout::create_interp(const Target* target)
{
const char* interp = this->options_.dynamic_linker();
if (interp == NULL)
{
interp = target->dynamic_linker();
gold_assert(interp != NULL);
}
size_t len = strlen(interp) + 1;
Output_section_data* odata = new Output_data_const(interp, len, 1);
const char* interp_name = this->namepool_.add(".interp", false, NULL);
Output_section* osec = this->make_output_section(interp_name,
elfcpp::SHT_PROGBITS,
elfcpp::SHF_ALLOC);
osec->add_output_section_data(odata);
Output_segment* oseg = new Output_segment(elfcpp::PT_INTERP, elfcpp::PF_R);
this->segment_list_.push_back(oseg);
oseg->add_initial_output_section(osec, elfcpp::PF_R);
}
// Finish the .dynamic section and PT_DYNAMIC segment.
void
Layout::finish_dynamic_section(const Input_objects* input_objects,
const Symbol_table* symtab)
{
Output_segment* oseg = new Output_segment(elfcpp::PT_DYNAMIC,
elfcpp::PF_R | elfcpp::PF_W);
this->segment_list_.push_back(oseg);
oseg->add_initial_output_section(this->dynamic_section_,
elfcpp::PF_R | elfcpp::PF_W);
Output_data_dynamic* const odyn = this->dynamic_data_;
for (Input_objects::Dynobj_iterator p = input_objects->dynobj_begin();
p != input_objects->dynobj_end();
++p)
{
// FIXME: Handle --as-needed.
odyn->add_string(elfcpp::DT_NEEDED, (*p)->soname());
}
if (parameters->output_is_shared())
{
const char* soname = this->options_.soname();
if (soname != NULL)
odyn->add_string(elfcpp::DT_SONAME, soname);
}
// FIXME: Support --init and --fini.
Symbol* sym = symtab->lookup("_init");
if (sym != NULL && sym->is_defined() && !sym->is_from_dynobj())
odyn->add_symbol(elfcpp::DT_INIT, sym);
sym = symtab->lookup("_fini");
if (sym != NULL && sym->is_defined() && !sym->is_from_dynobj())
odyn->add_symbol(elfcpp::DT_FINI, sym);
// FIXME: Support DT_INIT_ARRAY and DT_FINI_ARRAY.
// Add a DT_RPATH entry if needed.
const General_options::Dir_list& rpath(this->options_.rpath());
if (!rpath.empty())
{
std::string rpath_val;
for (General_options::Dir_list::const_iterator p = rpath.begin();
p != rpath.end();
++p)
{
if (rpath_val.empty())
rpath_val = p->name();
else
{
// Eliminate duplicates.
General_options::Dir_list::const_iterator q;
for (q = rpath.begin(); q != p; ++q)
if (q->name() == p->name())
break;
if (q == p)
{
rpath_val += ':';
rpath_val += p->name();
}
}
}
odyn->add_string(elfcpp::DT_RPATH, rpath_val);
}
// Look for text segments that have dynamic relocations.
bool have_textrel = false;
for (Segment_list::const_iterator p = this->segment_list_.begin();
p != this->segment_list_.end();
++p)
{
if (((*p)->flags() & elfcpp::PF_W) == 0
&& (*p)->dynamic_reloc_count() > 0)
{
have_textrel = true;
break;
}
}
// Add a DT_FLAGS entry. We add it even if no flags are set so that
// post-link tools can easily modify these flags if desired.
unsigned int flags = 0;
if (have_textrel)
{
// Add a DT_TEXTREL for compatibility with older loaders.
odyn->add_constant(elfcpp::DT_TEXTREL, 0);
flags |= elfcpp::DF_TEXTREL;
}
if (parameters->output_is_shared() && this->has_static_tls())
flags |= elfcpp::DF_STATIC_TLS;
odyn->add_constant(elfcpp::DT_FLAGS, flags);
}
// The mapping of .gnu.linkonce section names to real section names.
#define MAPPING_INIT(f, t) { f, sizeof(f) - 1, t, sizeof(t) - 1 }
const Layout::Linkonce_mapping Layout::linkonce_mapping[] =
{
MAPPING_INIT("d.rel.ro", ".data.rel.ro"), // Must be before "d".
MAPPING_INIT("t", ".text"),
MAPPING_INIT("r", ".rodata"),
MAPPING_INIT("d", ".data"),
MAPPING_INIT("b", ".bss"),
MAPPING_INIT("s", ".sdata"),
MAPPING_INIT("sb", ".sbss"),
MAPPING_INIT("s2", ".sdata2"),
MAPPING_INIT("sb2", ".sbss2"),
MAPPING_INIT("wi", ".debug_info"),
MAPPING_INIT("td", ".tdata"),
MAPPING_INIT("tb", ".tbss"),
MAPPING_INIT("lr", ".lrodata"),
MAPPING_INIT("l", ".ldata"),
MAPPING_INIT("lb", ".lbss"),
};
#undef MAPPING_INIT
const int Layout::linkonce_mapping_count =
sizeof(Layout::linkonce_mapping) / sizeof(Layout::linkonce_mapping[0]);
// Return the name of the output section to use for a .gnu.linkonce
// section. This is based on the default ELF linker script of the old
// GNU linker. For example, we map a name like ".gnu.linkonce.t.foo"
// to ".text". Set *PLEN to the length of the name. *PLEN is
// initialized to the length of NAME.
const char*
Layout::linkonce_output_name(const char* name, size_t *plen)
{
const char* s = name + sizeof(".gnu.linkonce") - 1;
if (*s != '.')
return name;
++s;
const Linkonce_mapping* plm = linkonce_mapping;
for (int i = 0; i < linkonce_mapping_count; ++i, ++plm)
{
if (strncmp(s, plm->from, plm->fromlen) == 0 && s[plm->fromlen] == '.')
{
*plen = plm->tolen;
return plm->to;
}
}
return name;
}
// Choose the output section name to use given an input section name.
// Set *PLEN to the length of the name. *PLEN is initialized to the
// length of NAME.
const char*
Layout::output_section_name(const char* name, size_t* plen)
{
if (Layout::is_linkonce(name))
{
// .gnu.linkonce sections are laid out as though they were named
// for the sections are placed into.
return Layout::linkonce_output_name(name, plen);
}
// gcc 4.3 generates the following sorts of section names when it
// needs a section name specific to a function:
// .text.FN
// .rodata.FN
// .sdata2.FN
// .data.FN
// .data.rel.FN
// .data.rel.local.FN
// .data.rel.ro.FN
// .data.rel.ro.local.FN
// .sdata.FN
// .bss.FN
// .sbss.FN
// .tdata.FN
// .tbss.FN
// The GNU linker maps all of those to the part before the .FN,
// except that .data.rel.local.FN is mapped to .data, and
// .data.rel.ro.local.FN is mapped to .data.rel.ro. The sections
// beginning with .data.rel.ro.local are grouped together.
// For an anonymous namespace, the string FN can contain a '.'.
// Also of interest: .rodata.strN.N, .rodata.cstN, both of which the
// GNU linker maps to .rodata.
// The .data.rel.ro sections enable a security feature triggered by
// the -z relro option. Section which need to be relocated at
// program startup time but which may be readonly after startup are
// grouped into .data.rel.ro. They are then put into a PT_GNU_RELRO
// segment. The dynamic linker will make that segment writable,
// perform relocations, and then make it read-only. FIXME: We do
// not yet implement this optimization.
// It is hard to handle this in a principled way.
// These are the rules we follow:
// If the section name has no initial '.', or no dot other than an
// initial '.', we use the name unchanged (i.e., "mysection" and
// ".text" are unchanged).
// If the name starts with ".data.rel.ro" we use ".data.rel.ro".
// Otherwise, we drop the second '.' and everything that comes after
// it (i.e., ".text.XXX" becomes ".text").
const char* s = name;
if (*s != '.')
return name;
++s;
const char* sdot = strchr(s, '.');
if (sdot == NULL)
return name;
const char* const data_rel_ro = ".data.rel.ro";
if (strncmp(name, data_rel_ro, strlen(data_rel_ro)) == 0)
{
*plen = strlen(data_rel_ro);
return data_rel_ro;
}
*plen = sdot - name;
return name;
}
// Record the signature of a comdat section, and return whether to
// include it in the link. If GROUP is true, this is a regular
// section group. If GROUP is false, this is a group signature
// derived from the name of a linkonce section. We want linkonce
// signatures and group signatures to block each other, but we don't
// want a linkonce signature to block another linkonce signature.
bool
Layout::add_comdat(const char* signature, bool group)
{
std::string sig(signature);
std::pair<Signatures::iterator, bool> ins(
this->signatures_.insert(std::make_pair(sig, group)));
if (ins.second)
{
// This is the first time we've seen this signature.
return true;
}
if (ins.first->second)
{
// We've already seen a real section group with this signature.
return false;
}
else if (group)
{
// This is a real section group, and we've already seen a
// linkonce section with this signature. Record that we've seen
// a section group, and don't include this section group.
ins.first->second = true;
return false;
}
else
{
// We've already seen a linkonce section and this is a linkonce
// section. These don't block each other--this may be the same
// symbol name with different section types.
return true;
}
}
// Store the allocated sections into the section list.
void
Layout::get_allocated_sections(Section_list* section_list) const
{
for (Section_list::const_iterator p = this->section_list_.begin();
p != this->section_list_.end();
++p)
if (((*p)->flags() & elfcpp::SHF_ALLOC) != 0)
section_list->push_back(*p);
}
// Create an output segment.
Output_segment*
Layout::make_output_segment(elfcpp::Elf_Word type, elfcpp::Elf_Word flags)
{
Output_segment* oseg = new Output_segment(type, flags);
this->segment_list_.push_back(oseg);
return oseg;
}
// Write out the Output_sections. Most won't have anything to write,
// since most of the data will come from input sections which are
// handled elsewhere. But some Output_sections do have Output_data.
void
Layout::write_output_sections(Output_file* of) const
{
for (Section_list::const_iterator p = this->section_list_.begin();
p != this->section_list_.end();
++p)
{
if (!(*p)->after_input_sections())
(*p)->write(of);
}
}
// Write out data not associated with a section or the symbol table.
void
Layout::write_data(const Symbol_table* symtab, Output_file* of) const
{
if (!parameters->strip_all())
{
const Output_section* symtab_section = this->symtab_section_;
for (Section_list::const_iterator p = this->section_list_.begin();
p != this->section_list_.end();
++p)
{
if ((*p)->needs_symtab_index())
{
gold_assert(symtab_section != NULL);
unsigned int index = (*p)->symtab_index();
gold_assert(index > 0 && index != -1U);
off_t off = (symtab_section->offset()
+ index * symtab_section->entsize());
symtab->write_section_symbol(*p, of, off);
}
}
}
const Output_section* dynsym_section = this->dynsym_section_;
for (Section_list::const_iterator p = this->section_list_.begin();
p != this->section_list_.end();
++p)
{
if ((*p)->needs_dynsym_index())
{
gold_assert(dynsym_section != NULL);
unsigned int index = (*p)->dynsym_index();
gold_assert(index > 0 && index != -1U);
off_t off = (dynsym_section->offset()
+ index * dynsym_section->entsize());
symtab->write_section_symbol(*p, of, off);
}
}
// Write out the Output_data which are not in an Output_section.
for (Data_list::const_iterator p = this->special_output_list_.begin();
p != this->special_output_list_.end();
++p)
(*p)->write(of);
}
// Write out the Output_sections which can only be written after the
// input sections are complete.
void
Layout::write_sections_after_input_sections(Output_file* of)
{
// Determine the final section offsets, and thus the final output
// file size. Note we finalize the .shstrab last, to allow the
// after_input_section sections to modify their section-names before
// writing.
if (this->any_postprocessing_sections_)
{
off_t off = this->output_file_size_;
off = this->set_section_offsets(off, POSTPROCESSING_SECTIONS_PASS);
// Now that we've finalized the names, we can finalize the shstrab.
off =
this->set_section_offsets(off,
STRTAB_AFTER_POSTPROCESSING_SECTIONS_PASS);
if (off > this->output_file_size_)
{
of->resize(off);
this->output_file_size_ = off;
}
}
for (Section_list::const_iterator p = this->section_list_.begin();
p != this->section_list_.end();
++p)
{
if ((*p)->after_input_sections())
(*p)->write(of);
}
this->section_headers_->write(of);
}
// Print statistical information to stderr. This is used for --stats.
void
Layout::print_stats() const
{
this->namepool_.print_stats("section name pool");
this->sympool_.print_stats("output symbol name pool");
this->dynpool_.print_stats("dynamic name pool");
for (Section_list::const_iterator p = this->section_list_.begin();
p != this->section_list_.end();
++p)
(*p)->print_merge_stats();
}
// Write_sections_task methods.
// We can always run this task.
Task_token*
Write_sections_task::is_runnable()
{
return NULL;
}
// We need to unlock both OUTPUT_SECTIONS_BLOCKER and FINAL_BLOCKER
// when finished.
void
Write_sections_task::locks(Task_locker* tl)
{
tl->add(this, this->output_sections_blocker_);
tl->add(this, this->final_blocker_);
}
// Run the task--write out the data.
void
Write_sections_task::run(Workqueue*)
{
this->layout_->write_output_sections(this->of_);
}
// Write_data_task methods.
// We can always run this task.
Task_token*
Write_data_task::is_runnable()
{
return NULL;
}
// We need to unlock FINAL_BLOCKER when finished.
void
Write_data_task::locks(Task_locker* tl)
{
tl->add(this, this->final_blocker_);
}
// Run the task--write out the data.
void
Write_data_task::run(Workqueue*)
{
this->layout_->write_data(this->symtab_, this->of_);
}
// Write_symbols_task methods.
// We can always run this task.
Task_token*
Write_symbols_task::is_runnable()
{
return NULL;
}
// We need to unlock FINAL_BLOCKER when finished.
void
Write_symbols_task::locks(Task_locker* tl)
{
tl->add(this, this->final_blocker_);
}
// Run the task--write out the symbols.
void
Write_symbols_task::run(Workqueue*)
{
this->symtab_->write_globals(this->input_objects_, this->sympool_,
this->dynpool_, this->of_);
}
// Write_after_input_sections_task methods.
// We can only run this task after the input sections have completed.
Task_token*
Write_after_input_sections_task::is_runnable()
{
if (this->input_sections_blocker_->is_blocked())
return this->input_sections_blocker_;
return NULL;
}
// We need to unlock FINAL_BLOCKER when finished.
void
Write_after_input_sections_task::locks(Task_locker* tl)
{
tl->add(this, this->final_blocker_);
}
// Run the task.
void
Write_after_input_sections_task::run(Workqueue*)
{
this->layout_->write_sections_after_input_sections(this->of_);
}
// Close_task_runner methods.
// Run the task--close the file.
void
Close_task_runner::run(Workqueue*, const Task*)
{
this->of_->close();
}
// Instantiate the templates we need. We could use the configure
// script to restrict this to only the ones for implemented targets.
#ifdef HAVE_TARGET_32_LITTLE
template
Output_section*
Layout::layout<32, false>(Sized_relobj<32, false>* object, unsigned int shndx,
const char* name,
const elfcpp::Shdr<32, false>& shdr,
unsigned int, unsigned int, off_t*);
#endif
#ifdef HAVE_TARGET_32_BIG
template
Output_section*
Layout::layout<32, true>(Sized_relobj<32, true>* object, unsigned int shndx,
const char* name,
const elfcpp::Shdr<32, true>& shdr,
unsigned int, unsigned int, off_t*);
#endif
#ifdef HAVE_TARGET_64_LITTLE
template
Output_section*
Layout::layout<64, false>(Sized_relobj<64, false>* object, unsigned int shndx,
const char* name,
const elfcpp::Shdr<64, false>& shdr,
unsigned int, unsigned int, off_t*);
#endif
#ifdef HAVE_TARGET_64_BIG
template
Output_section*
Layout::layout<64, true>(Sized_relobj<64, true>* object, unsigned int shndx,
const char* name,
const elfcpp::Shdr<64, true>& shdr,
unsigned int, unsigned int, off_t*);
#endif
#ifdef HAVE_TARGET_32_LITTLE
template
Output_section*
Layout::layout_eh_frame<32, false>(Sized_relobj<32, false>* object,
const unsigned char* symbols,
off_t symbols_size,
const unsigned char* symbol_names,
off_t symbol_names_size,
unsigned int shndx,
const elfcpp::Shdr<32, false>& shdr,
unsigned int reloc_shndx,
unsigned int reloc_type,
off_t* off);
#endif
#ifdef HAVE_TARGET_32_BIG
template
Output_section*
Layout::layout_eh_frame<32, true>(Sized_relobj<32, true>* object,
const unsigned char* symbols,
off_t symbols_size,
const unsigned char* symbol_names,
off_t symbol_names_size,
unsigned int shndx,
const elfcpp::Shdr<32, true>& shdr,
unsigned int reloc_shndx,
unsigned int reloc_type,
off_t* off);
#endif
#ifdef HAVE_TARGET_64_LITTLE
template
Output_section*
Layout::layout_eh_frame<64, false>(Sized_relobj<64, false>* object,
const unsigned char* symbols,
off_t symbols_size,
const unsigned char* symbol_names,
off_t symbol_names_size,
unsigned int shndx,
const elfcpp::Shdr<64, false>& shdr,
unsigned int reloc_shndx,
unsigned int reloc_type,
off_t* off);
#endif
#ifdef HAVE_TARGET_64_BIG
template
Output_section*
Layout::layout_eh_frame<64, true>(Sized_relobj<64, true>* object,
const unsigned char* symbols,
off_t symbols_size,
const unsigned char* symbol_names,
off_t symbol_names_size,
unsigned int shndx,
const elfcpp::Shdr<64, true>& shdr,
unsigned int reloc_shndx,
unsigned int reloc_type,
off_t* off);
#endif
} // End namespace gold.
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