Elf sample code: elf

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ELF : libelf examples

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file: elf_copy.c

1 /* 2 * Copy an elf to an ELF object. 3 * This is a demo program for libraries libelf and gelf. The resulting elf file 4 * may not be loadable due to offset changes. 5 * 2007.11.10 19:52:23 Emmanuel AZENCOT 6 * Creation 7 * Sun Nov 22 20:33:20 CET 2009 8 * bug fix in error message \%s\" 9 * 10 * build : gcc -Wall -g -o elf_copy -lelf elf_copy.c 11 * TODO 12 * output a working binary 13 */ 14 #include <string.h> 15 #include <stdio.h> 16 #include <stdlib.h> 17 #include <sysexits.h> 18 #include <unistd.h> 19 #include <fcntl.h> 20 #include <errno.h> 21 22 #include <err.h> 23 #include <gelf.h> 24 25 #define /*X*/ errx(code, fmt, args...) { \ 26 fprintf(stderr,#code ": error in file %s at line %d in function %s:", __FILE__,__LINE__,__FUNCTION__); \ 27 fprintf(stderr,fmt "\n", ##args); \ 28 exit(1); \ 29 } 30 #define /*X*/ merrx(code, fmt, args...) { \ 31 fprintf(stderr,#code ": error in file %s at line %d in function %s:", __FILE__,__LINE__,__FUNCTION__); \ 32 fprintf(stderr,fmt "\n", ##args); \ 33 return 0; \ 34 } 35 36 int /*X*/ melf_cpy_scn (Elf *elf_out, Elf_Scn *scn_out, Elf *elf_in, Elf_Scn *scn_in) { 37 Elf_Data *data_in, *data_out; 38 GElf_Shdr shdr_in, shdr_out; 39 size_t n; 40 41 if (gelf_getshdr(scn_in, &shdr_in) != &shdr_in) 42 merrx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 43 44 data_in = NULL; n = 0; 45 while (n < shdr_in.sh_size && (data_in = elf_getdata(scn_in, data_in)) != NULL) { 46 if ((data_out = elf_newdata(scn_out)) == NULL) 47 merrx(EX_SOFTWARE, "elf_newdata() failed: %s.", elf_errmsg(-1)); 48 *data_out = *data_in; 49 } 50 51 if ( gelf_getshdr(scn_out, &shdr_out) != &shdr_out) 52 merrx(EX_SOFTWARE, "gelf_getshdr() failed: %s.", elf_errmsg(-1)); 53 54 shdr_out = shdr_in; 55 56 if ( gelf_update_shdr (scn_out, &shdr_out) == 0) 57 merrx(EX_SOFTWARE, "gelf_update_shdr() failed: %s.", elf_errmsg(-1)); 58 59 return 1; 60 } 61 int /*X*/ main(int argc, char *argv[]) { 62 int fd_in = -1, fd_out = -1; 63 Elf *elf_in = 0, *elf_out = 0; 64 65 Elf_Scn *scn_in, *scn_out; 66 GElf_Ehdr ehdr_in, ehdr_out; 67 68 size_t shstrndx; 69 70 int scn_index = 0; 71 72 if (argc != 3) 73 errx(EX_USAGE, "USAGE: %s in-file-name out-file-name", argv[0]); 74 75 if (elf_version(EV_CURRENT) == EV_NONE) 76 errx(EX_SOFTWARE, "ELF library initialization failed: %s", elf_errmsg(-1)); 77 78 if ((fd_in = open(argv[1], O_RDONLY, 0)) < 0) 79 err(EX_NOINPUT, "open \"%s\" failed", argv[1]); 80 81 if ((elf_in = elf_begin(fd_in, ELF_C_READ, NULL)) == NULL) 82 errx(EX_SOFTWARE, "elf_begin() failed: %s.", elf_errmsg(-1)); 83 84 if (gelf_getehdr(elf_in, &ehdr_in) != &ehdr_in) 85 errx(EX_SOFTWARE, "gelf_getehdr() failed: %s.", elf_errmsg(-1)); 86 87 /* get string section index for section names */ 88 if (elf_getshstrndx(elf_in, &shstrndx) != 0) 89 errx(EX_SOFTWARE, "getshstrndx() failed: %s, %d.", elf_errmsg(-1), shstrndx); 90 91 /* Checks and warns */ 92 if ( elf_kind(elf_in) != ELF_K_ELF ) { 93 fprintf(stderr, "%s : %s must be an ELF file.\n", argv[0], argv[1]); 94 exit(1); 95 } 96 97 printf("Elf %s have %d sections\n", argv[1], ehdr_in.e_shnum); 98 /* opent output elf */ 99 if ((fd_out = open(argv[2], O_WRONLY|O_CREAT, 0777)) < 0) 100 errx(EX_OSERR, "open \"%s\" failed", argv[2]); 101 102 if ((elf_out = elf_begin(fd_out, ELF_C_WRITE, NULL)) == NULL) 103 errx(EX_SOFTWARE, "elf_begin() failed: %s.", elf_errmsg(-1)); 104 105 /* create new elf header */ 106 if ( gelf_newehdr(elf_out, ehdr_in.e_ident[EI_CLASS]) == 0) 107 errx(EX_SOFTWARE, "gelf_newehdr() failed: %s.", elf_errmsg(-1)); 108 if ( gelf_getehdr(elf_out, &ehdr_out) != &ehdr_out) 109 errx(EX_SOFTWARE, "gelf_getehdr() failed: %s.", elf_errmsg(-1)); 110 ehdr_out = ehdr_in; 111 ehdr_out.e_ehsize = 0; 112 ehdr_out.e_phentsize = 0; 113 ehdr_out.e_phnum = 0; 114 ehdr_out.e_shentsize = 0; 115 ehdr_out.e_shnum = 0; 116 if ( gelf_update_ehdr (elf_out, &ehdr_out) == 0) 117 errx(EX_SOFTWARE, "gelf_update_ehdr() failed: %s.", elf_errmsg(-1)); 118 119 { 120 GElf_Phdr phdr_in, phdr_out; 121 int ph_ndx; 122 123 if ( ehdr_in.e_phnum && gelf_newphdr (elf_out, ehdr_in.e_phnum) == 0 ) 124 errx(EX_SOFTWARE, "gelf_newphdr() failed: %s.", elf_errmsg(-1)); 125 126 for ( ph_ndx = 0; ph_ndx < ehdr_in.e_phnum; ++ph_ndx ) { 127 printf("Copying prog header %d\n", ph_ndx); 128 129 if ( gelf_getphdr (elf_in, ph_ndx, &phdr_in) != &phdr_in ) 130 errx(EX_SOFTWARE, "gelf_getphdr() failed: %s.", elf_errmsg(-1)); 131 132 if ( gelf_getphdr (elf_out, ph_ndx, &phdr_out) != &phdr_out ) 133 errx(EX_SOFTWARE, "gelf_getphdr() failed: %s.", elf_errmsg(-1)); 134 phdr_out = phdr_in; 135 136 if ( gelf_update_phdr (elf_out, ph_ndx, &phdr_out) == 0) 137 errx(EX_SOFTWARE, "gelf_update_phdr() failed: %s.", elf_errmsg(-1)); 138 } 139 } 140 /* copy sections to new elf */ 141 for ( scn_index = 1; scn_index < ehdr_in.e_shnum; scn_index++ ) { 142 if ( (scn_in = elf_getscn(elf_in, scn_index)) == NULL) 143 errx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 144 if ((scn_out = elf_newscn(elf_out)) == NULL) 145 errx(EX_SOFTWARE, "elf_newscn() failed: %s.", elf_errmsg(-1)); 146 if ( melf_cpy_scn (elf_out, scn_out, elf_in, scn_in) == 0 ) 147 errx(EX_SOFTWARE, "melf_cpy_scn() failed: %s.", elf_errmsg(-1)); 148 } 149 /* Adjust section offset in Phrs */ 150 { 151 GElf_Phdr phdr_in, phdr_out; 152 int ph_ndx; 153 154 if ( ehdr_in.e_phnum && gelf_newphdr (elf_out, ehdr_in.e_phnum) == 0 ) 155 errx(EX_SOFTWARE, "gelf_newphdr() failed: %s.", elf_errmsg(-1)); 156 157 for ( ph_ndx = 0; ph_ndx < ehdr_in.e_phnum; ++ph_ndx ) { 158 GElf_Shdr shdr_out; 159 if ( gelf_getphdr (elf_in, ph_ndx, &phdr_in) != &phdr_in ) 160 errx(EX_SOFTWARE, "gelf_getphdr() failed: %s.", elf_errmsg(-1)); 161 162 if ( gelf_getphdr (elf_out, ph_ndx, &phdr_out) != &phdr_out ) 163 errx(EX_SOFTWARE, "gelf_getphdr() failed: %s.", elf_errmsg(-1)); 164 165 if ( !phdr_in.p_offset || phdr_in.p_type == PT_PHDR ) continue; 166 /* Get section offset from input phdr */ 167 if ( (scn_in = gelf_offscn (elf_in, phdr_in.p_offset )) == NULL) 168 errx(EX_SOFTWARE, "gelf_offscn() failed: %s.", elf_errmsg(-1)); 169 /* Convert to section index */ 170 if ( (scn_index = elf_ndxscn (scn_in)) == 0) 171 fprintf(stderr, "elf_ndxscn() failed for phdr %d : %s.", ph_ndx, elf_errmsg(-1)); 172 /* get out section at same index from out elf */ 173 if ( (scn_out = elf_getscn(elf_out, scn_index)) == NULL) 174 errx(EX_SOFTWARE, "getshdr() failed: %s.", elf_errmsg(-1)); 175 /* get out section offset from section header */ 176 if ( gelf_getshdr(scn_out, &shdr_out) != &shdr_out) 177 merrx(EX_SOFTWARE, "gelf_getshdr() failed: %s.", elf_errmsg(-1)); 178 179 phdr_out.p_offset = shdr_out.sh_offset; 180 181 if ( gelf_update_phdr (elf_out, ph_ndx, &phdr_out) == 0) 182 errx(EX_SOFTWARE, "gelf_update_phdr() failed: %s.", elf_errmsg(-1)); 183 } 184 } 185 if (elf_update(elf_out, ELF_C_WRITE) < 0) 186 errx(EX_SOFTWARE, "elf_update() failed: %s.", elf_errmsg(-1)); 187 188 elf_end(elf_out); 189 close(fd_out); 190 elf_end(elf_in); 191 close(fd_in); 192 193 exit(EX_OK); 194 } 195