mirror of
https://github.com/serge1/ELFIO.git
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118 lines
4.1 KiB
C++
118 lines
4.1 KiB
C++
/*
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* This example shows how to create ELF object file for Linux on x86
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*
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* Instructions:
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* 1. Compile and link this file with ELFIO library
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* g++ write_obj.cpp -o writer_obj
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* 2. Execute result file write_obj
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* ./write_obj
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* 3. Link output file hello.o:
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* ld -o hello hello.o
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* 4. Run the result file:
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* ./hello
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*/
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#include <elfio/elfio.hpp>
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using namespace ELFIO;
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int main( void )
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{
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elfio writer;
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// You can't proceed before this function call!
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writer.create( ELFCLASS64, ELFDATA2LSB );
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writer.set_os_abi( ELFOSABI_LINUX );
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writer.set_type( ET_REL );
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writer.set_machine( EM_X86_64 );
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// This is our code
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char text[] = {
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'\xB8', '\x04', '\x00', '\x00', '\x00', // mov eax, 4
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'\xBB', '\x01', '\x00', '\x00', '\x00', // mov ebx, 1
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'\xB9', '\x00', '\x00', '\x00', '\x00', // mov ecx, msg
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'\xBA', '\x0E', '\x00', '\x00', '\x00', // mov edx, 14
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'\xCD', '\x80', // int 0x80
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'\xB8', '\x01', '\x00', '\x00', '\x00', // mov eax, 1
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'\xCD', '\x80', // int 0x80
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'\x48', '\x65', '\x6C', '\x6C', '\x6F', // msg: db 'Hello, World!', 10
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'\x2C', '\x20', '\x57', '\x6F', '\x72',
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'\x6C', '\x64', '\x21', '\x0A' };
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Elf64_Addr place_to_adjust = 11;
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// Create code section
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section* text_sec = writer.sections.add( ".text" );
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text_sec->set_type( SHT_PROGBITS );
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text_sec->set_flags( SHF_ALLOC | SHF_EXECINSTR );
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text_sec->set_addr_align( 0x10 );
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text_sec->set_data( text, sizeof( text ) );
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// Create string table section
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section* str_sec = writer.sections.add( ".strtab" );
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str_sec->set_type( SHT_STRTAB );
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// Create string table writer
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string_section_accessor stra( str_sec );
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// Add label name
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Elf32_Word str_index = stra.add_string( "msg" );
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// Create symbol table section
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section* sym_sec = writer.sections.add( ".symtab" );
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sym_sec->set_type( SHT_SYMTAB );
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sym_sec->set_info( 1 );
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sym_sec->set_addr_align( 0x4 );
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sym_sec->set_entry_size( writer.get_default_entry_size( SHT_SYMTAB ) );
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sym_sec->set_link( str_sec->get_index() );
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// Create symbol table writer
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symbol_section_accessor syma( writer, sym_sec );
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// Add symbol entry (msg has offset == 29)
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Elf_Word sym_to_adjust = syma.add_symbol(
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str_index, 29, 0, STB_GLOBAL, STT_OBJECT, 0, text_sec->get_index() );
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// Another way to add symbol
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syma.add_symbol( stra, "_start", 0x00000000, 0, STB_WEAK, STT_FUNC, 0,
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text_sec->get_index() );
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// Create relocation table section
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section* rel_sec = writer.sections.add( ".rel.text" );
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rel_sec->set_type( SHT_REL );
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rel_sec->set_info( text_sec->get_index() );
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rel_sec->set_addr_align( 0x4 );
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rel_sec->set_entry_size( writer.get_default_entry_size( SHT_REL ) );
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rel_sec->set_link( sym_sec->get_index() );
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// Create relocation table writer
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relocation_section_accessor rela( writer, rel_sec );
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// Add relocation entry (adjust address at offset 11)
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rela.add_entry( place_to_adjust, sym_to_adjust,
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(unsigned char)R_386_RELATIVE );
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// Another method to add the same relocation entry at one step is:
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// rela.add_entry( stra, "msg",
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// syma, 29, 0,
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// ELF_ST_INFO( STB_GLOBAL, STT_OBJECT ), 0,
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// text_sec->get_index(),
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// place_to_adjust, (unsigned char)R_386_RELATIVE );
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// Create note section
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section* note_sec = writer.sections.add( ".note" );
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note_sec->set_type( SHT_NOTE );
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note_section_accessor note_writer( writer, note_sec );
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note_writer.add_note( 0x01, "Created by ELFIO", 0, 0 );
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char descr[6] = { 0x31, 0x32, 0x33, 0x34, 0x35, 0x36 };
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note_writer.add_note( 0x01, "Never easier!", descr, sizeof( descr ) );
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// We don't use local symbols here. There is no need to rearrange them.
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// But, for the completeness, we do this just prior 'save'
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syma.arrange_local_symbols( [&]( Elf_Xword first, Elf_Xword second ) {
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rela.swap_symbols( first, second );
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} );
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// Create ELF object file
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writer.save( "hello.o" );
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return 0;
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}
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