test/external_tools/elf_creator.c

   1 /* Loosely based on the code in a Knol by Roberto Garcia Lopez:
   2 **
   3 ** http://knol.google.com/k/roberto-garca-lpez/creating-elf-relocatable-object-files/1ohwel4gqkcn2/3#
   4 **
   5 ** Note: This file is released under the terms of the LGPL2 license.
   6 */
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9 #include <fcntl.h>
  10 #include <unistd.h>
  11 #include <libelf.h>
  12 #include <err.h>
  13 #include <sysexits.h>
  14
  15
  16 const char* OUTFILE = "generated.o";
  17
  18 // Definition of the default string table section ".shstrtab"
  19 const char defaultStrTable[] =
  20 {
  21     /* offset 00 */ '\0',  // The NULL section
  22     /* offset 01 */ '.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', '\0',
  23     /* offset 11 */ '.', 's', 't', 'r', 't', 'a', 'b', '\0',
  24     /* offset 19 */ '.', 's', 'y', 'm', 't', 'a', 'b', '\0',
  25     /* offset 27 */ '.', 'c', 'o', 'm', 'm', 'e', 'n', 't', '\0',
  26     /* offset 36 */ '.', 'b', 's', 's', '\0',
  27     /* offset 41 */ '.', 'd', 'a', 't', 'a', '\0',
  28     /* offset 47 */ '.', 'r', 'e', 'l', '.', 't', 'e', 'x', 't', '\0',
  29     /* offset 57 */ '.', 't', 'e', 'x', 't', '\0'
  30 };
  31
  32 const char defaultStrTableLen = sizeof(defaultStrTable);
  33
  34 // Offsets of section names in the string table
  35 const char _shstrtab_offset = 1;
  36 const char _strtab_offset = 11;
  37 const char _symtab_offset = 19;
  38 const char _text_offset = 57;
  39
  40 // Position of sections within the object file
  41 const char _shstrtab = 1;
  42 const char _strtab = 2;
  43 const char _symtab = 3;
  44 const char _text = 4;
  45
  46 const char TEXT_CONTENTS[] = {0x91, 0x92, 0x93, 0x94};
  47
  48
  49 //----------------------------------------------------------------------------
  50
  51 int main()
  52 {
  53     int FileDes;
  54     Elf *pElf;
  55     Elf32_Ehdr *pEhdr;
  56     Elf32_Shdr *pShdr;
  57     Elf_Scn *pScn;
  58     Elf_Data *pData;
  59
  60     // Create the ELF header
  61     if (elf_version(EV_CURRENT) == EV_NONE) // It must appear before "elf_begin()"
  62         errx(EX_SOFTWARE, "ELF library initialization failed: %s", elf_errmsg(-1));
  63
  64     if ((FileDes = open(OUTFILE, O_CREAT | O_WRONLY | O_TRUNC, 0777)) < 0)
  65         errx(EX_OSERR, "open \"%s\" failed", "compiled.o");
  66
  67     if ((pElf = elf_begin(FileDes, ELF_C_WRITE, NULL)) == NULL)  // 3rd argument is ignored for "ELF_C_WRITE"
  68         errx(EX_SOFTWARE, "elf_begin() failed: %s.", elf_errmsg(-1));
  69
  70     if ((pEhdr = elf32_newehdr(pElf)) == NULL)
  71         errx(EX_SOFTWARE, "elf32_newehdr() failed: %s", elf_errmsg(-1));
  72
  73     pEhdr->e_ident[EI_CLASS] = ELFCLASS32;  // Defined by Intel architecture
  74     pEhdr->e_ident[EI_DATA] = ELFDATA2LSB;  // Defined by Intel architecture
  75     pEhdr->e_machine = EM_386;  // Intel architecture
  76     pEhdr->e_type = ET_REL;   // Relocatable file (object file)
  77     pEhdr->e_shstrndx = _shstrtab;    // Point to the shstrtab section
  78
  79     // Create the section "default section header string table (.shstrtab)"
  80     if ((pScn = elf_newscn(pElf)) == NULL)
  81         errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1));
  82     if ((pData = elf_newdata(pScn)) == NULL)
  83         errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1));
  84
  85     pData->d_align = 1;
  86     pData->d_buf = (void *) defaultStrTable;
  87     pData->d_type = ELF_T_BYTE;
  88     pData->d_size = defaultStrTableLen;
  89
  90     if ((pShdr = elf32_getshdr(pScn)) == NULL)
  91         errx(EX_SOFTWARE, "elf32_etshdr() failed: %s.", elf_errmsg(-1));
  92
  93     pShdr->sh_name = _shstrtab_offset;  // Point to the name of the section
  94     pShdr->sh_type = SHT_STRTAB;
  95     pShdr->sh_flags = 0;
  96
  97     // Create the section ".strtab"
  98     if ((pScn = elf_newscn(pElf)) == NULL)
  99         errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1));
 100     if ((pData = elf_newdata(pScn)) == NULL)
 101         errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1));
 102
 103     const char strtab[] = {0, 'g', 'e', 'n', 'e', 'r', 'a', 't', 'e', 'd', '.','x', 0, '_', 's', 't', 'a', 'r', 't', 0};
 104
 105     pData->d_align = 1;
 106     pData->d_buf = (void *) strtab;
 107     pData->d_type = ELF_T_BYTE;
 108     pData->d_size = sizeof(strtab);
 109
 110     if ((pShdr = elf32_getshdr(pScn)) == NULL)
 111         errx(EX_SOFTWARE, "elf32_etshdr() failed: %s.", elf_errmsg(-1));
 112
 113     pShdr->sh_name = _strtab_offset;
 114     pShdr->sh_type = SHT_STRTAB;
 115     pShdr->sh_flags = 0;
 116
 117     // Create the section ".symtab"
 118     if ((pScn = elf_newscn(pElf)) == NULL)
 119         errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1));
 120     if ((pData = elf_newdata(pScn)) == NULL)
 121         errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1));
 122
 123     Elf32_Sym x[4];
 124
 125     // Definition of the undefined section (this must be the first item by the definition of TIS ELF)
 126     x[0].st_name = 0;
 127     x[0].st_value = 0;
 128     x[0].st_size = 0;
 129     x[0].st_info = 0;
 130     x[0].st_other = 0;
 131     x[0].st_shndx = SHN_UNDEF;
 132
 133     // Definition of the name of the source file (this must be the second item by the definition in TIS ELF)
 134     x[1].st_name = 1;
 135     x[1].st_value = 0;
 136     x[1].st_size = 0;
 137     x[1].st_info = ELF32_ST_INFO(STB_LOCAL, STT_FILE); // This is the value that st_info must have (because of TIS ELF)
 138     x[1].st_other = 0;
 139     x[1].st_shndx = SHN_ABS;  // The section where the symbol is
 140
 141     // Definition of the ".text" section as a section in the ".symtab" section
 142     x[2].st_name = 0;
 143     x[2].st_value = 0;
 144     x[2].st_size = 0;
 145     x[2].st_info = ELF32_ST_INFO(STB_LOCAL, STT_SECTION);
 146     x[2].st_other = 0;
 147     x[2].st_shndx = _text;  // The section where the symbol is
 148
 149     // Definition of the "_start" symbol
 150     x[3].st_name = 13;  // Offset in the "strtab" section where the name start
 151     x[3].st_value = 0;
 152     x[3].st_size = 0;
 153     x[3].st_info = ELF32_ST_INFO(STB_GLOBAL, STT_NOTYPE);
 154     x[3].st_other = 0;
 155     x[3].st_shndx = _text;  // The section where the symbol is
 156
 157     pData->d_align = 4;
 158     pData->d_buf = (void *) x;
 159     pData->d_type = ELF_T_BYTE;
 160     pData->d_size = sizeof(x);
 161
 162     if ((pShdr = elf32_getshdr(pScn)) == NULL)
 163         errx(EX_SOFTWARE, "elf32_etshdr() failed: %s.", elf_errmsg(-1));
 164
 165     pShdr->sh_name = _symtab_offset;  // Point to the name of the section
 166     pShdr->sh_type = SHT_SYMTAB;
 167     pShdr->sh_flags = 0;
 168     pShdr->sh_link = _strtab;  // point to the section .strtab (the section that contain the strings)
 169     pShdr->sh_info = ELF32_ST_INFO(STB_LOCAL, 3);  // the second argument is beause of TIS ELF (One greater than the symbol table index of the last local symbol (binding STB_LOCAL))
 170
 171     // Create many sections named .text
 172     for (int i = 0; i < 70000; ++i) {
 173         if ((pScn = elf_newscn(pElf)) == NULL)
 174             errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1));
 175         if ((pData = elf_newdata(pScn)) == NULL)
 176             errx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1));
 177
 178         pData->d_align = 4;
 179         pData->d_buf = (void *)TEXT_CONTENTS;
 180         pData->d_type = ELF_T_BYTE;
 181         pData->d_size = sizeof(TEXT_CONTENTS);
 182
 183         if ((pShdr = elf32_getshdr(pScn)) == NULL)
 184             errx(EX_SOFTWARE, "elf32_etshdr() failed: %s.", elf_errmsg(-1));
 185
 186         pShdr->sh_name = _text_offset;
 187         pShdr->sh_type = SHT_PROGBITS;
 188         pShdr->sh_flags = SHF_ALLOC | SHF_EXECINSTR;
 189     }
 190
 191     // Update the sections internally
 192     if (elf_update(pElf, ELF_C_NULL) < 0)
 193         errx(EX_SOFTWARE, "elf_update(NULL) failed: %s.", elf_errmsg(-1));
 194     // Write the object file
 195     if (elf_update(pElf, ELF_C_WRITE) < 0)
 196         errx(EX_SOFTWARE, "elf_update() failed: %s.", elf_errmsg(-1));
 197     // Close all handles
 198     elf_end(pElf);
 199     close(FileDes);
 200     printf("Generated file: %s\n", OUTFILE);
 201
 202     return 0;
 203 }
 204