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// copy-relocs.h -- handle COPY relocations for gold -*- C++ -*-
// Copyright (C) 2006-2020 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.
#ifndef GOLD_COPY_RELOCS_H
#define GOLD_COPY_RELOCS_H
#include "elfcpp.h"
#include "reloc-types.h"
#include "output.h"
namespace gold
{
// This class is used to manage COPY relocations. We try to avoid
// them when possible. A COPY relocation may be required when an
// executable refers to a variable defined in a shared library. COPY
// relocations are problematic because they tie the executable to the
// exact size of the variable in the shared library. We can avoid
// them if all the references to the variable are in a writeable
// section. In that case we can simply use dynamic relocations.
// However, when scanning relocs, we don't know when we see the
// relocation whether we will be forced to use a COPY relocation or
// not. So we have to save the relocation during the reloc scanning,
// and then emit it as a dynamic relocation if necessary. This class
// implements that. It is used by the target specific code.
// The template parameter SH_TYPE is the type of the reloc section to
// be used for COPY relocs: elfcpp::SHT_REL or elfcpp::SHT_RELA.
template<int sh_type, int size, bool big_endian>
class Copy_relocs
{
private:
typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reloc;
public:
Copy_relocs(unsigned int copy_reloc_type)
: entries_(), copy_reloc_type_(copy_reloc_type), dynbss_(NULL),
dynrelro_(NULL)
{ }
// This is called while scanning relocs if we see a relocation
// against a symbol which may force us to generate a COPY reloc.
// SYM is the symbol. OBJECT is the object whose relocs we are
// scanning. The relocation is being applied to section SHNDX in
// OBJECT. OUTPUT_SECTION is the output section where section SHNDX
// will wind up. REL is the reloc itself. The Output_data_reloc
// section is where the dynamic relocs are put.
void
copy_reloc(Symbol_table*,
Layout*,
Sized_symbol<size>* sym,
Sized_relobj_file<size, big_endian>* object,
unsigned int shndx,
Output_section* output_section,
unsigned int r_type,
typename elfcpp::Elf_types<size>::Elf_Addr r_offset,
typename elfcpp::Elf_types<size>::Elf_Swxword r_addend,
Output_data_reloc<sh_type, true, size, big_endian>*);
// Return whether there are any saved relocations.
bool
any_saved_relocs() const
{ return !this->entries_.empty(); }
// Emit any saved relocations which turn out to be needed. This is
// called after all the relocs have been scanned.
void
emit(Output_data_reloc<sh_type, true, size, big_endian>*);
// Emit a COPY reloc.
void
emit_copy_reloc(Symbol_table*, Sized_symbol<size>*,
Output_data*, off_t,
Output_data_reloc<sh_type, true, size, big_endian>*);
protected:
typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
typedef typename elfcpp::Elf_types<size>::Elf_Addr Addend;
// This POD class holds the relocations we are saving. We will emit
// these relocations if it turns out that the symbol does not
// require a COPY relocation.
struct Copy_reloc_entry
{
Copy_reloc_entry(Symbol* sym, unsigned int reloc_type,
Sized_relobj_file<size, big_endian>* relobj,
unsigned int shndx,
Output_section* output_section,
Address address, Addend addend)
: sym_(sym), reloc_type_(reloc_type), relobj_(relobj),
shndx_(shndx), output_section_(output_section),
address_(address), addend_(addend)
{ }
Symbol* sym_;
unsigned int reloc_type_;
Sized_relobj_file<size, big_endian>* relobj_;
unsigned int shndx_;
Output_section* output_section_;
Address address_;
Addend addend_;
};
// Make a new COPY reloc and emit it.
void
make_copy_reloc(Symbol_table*, Layout*, Sized_symbol<size>*,
Sized_relobj_file<size, big_endian>* object,
Output_data_reloc<sh_type, true, size, big_endian>*);
// A list of relocs to be saved.
typedef std::vector<Copy_reloc_entry> Copy_reloc_entries;
// The list of relocs we are saving.
Copy_reloc_entries entries_;
private:
// Return whether we need a COPY reloc.
bool
need_copy_reloc(Sized_symbol<size>* gsym,
Sized_relobj_file<size, big_endian>* object,
unsigned int shndx) const;
// Save a reloc against SYM for possible emission later.
void
save(Symbol*,
Sized_relobj_file<size, big_endian>*,
unsigned int shndx,
Output_section*,
unsigned int r_type,
typename elfcpp::Elf_types<size>::Elf_Addr r_offset,
typename elfcpp::Elf_types<size>::Elf_Swxword r_addend);
// The target specific relocation type of the COPY relocation.
const unsigned int copy_reloc_type_;
// The dynamic BSS data which goes into the .bss section. This is
// where writable variables which require COPY relocations are placed.
Output_data_space* dynbss_;
// The dynamic read-only data, which goes into the .data.rel.ro section.
// This is where read-only variables which require COPY relocations are
// placed.
Output_data_space* dynrelro_;
};
} // End namespace gold.
#endif // !defined(GOLD_COPY_RELOCS_H)
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