/* * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code 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 * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ /* * Name: fix_empty_sec_hdr_flags.c * * Description: Remove the SHF_ALLOC flag from "empty" section headers. * An "empty" section header has sh_addr == 0 and sh_size == 0. * * This program is adapted from the example program shown on the * elf(3elf) man page and from code from the Solaris compiler * driver. */ #include #include #include #include #include #include static void failure(void); void main(int argc, char ** argv) { void * ehdr; /* ELF header */ unsigned int i; /* section counter */ int fd; /* descriptor for file */ Elf * elf; /* ELF descriptor */ char * elf_ident; /* ELF identity string */ char * elf_obj; /* elf_obj file */ int fix_count; /* number of flags fixed */ int is_elfclass64; /* is an ELFCLASS64 file? */ Elf_Scn * scn; /* ELF section descriptor */ void * shdr; /* ELF section header */ Elf_Data * shstrtab; /* ELF section header string table */ if (argc != 2) { (void) fprintf(stderr, "Usage: %s elf_obj\n", argv[0]); exit(2); } /* open the elf_obj */ elf_obj = argv[1]; if ((fd = open(elf_obj, O_RDWR)) == -1) { (void) fprintf(stderr, "%s: cannot open file.\n", elf_obj); exit(3); } (void) printf("Opening '%s' for update\n", elf_obj); (void) fflush(stdout); (void) elf_version(EV_CURRENT); /* coordinate ELF versions */ /* obtain the ELF descriptors from the input file */ if ((elf = elf_begin(fd, ELF_C_RDWR, NULL)) == NULL) { failure(); } /* determine if ELFCLASS64 or not? */ elf_ident = elf_getident(elf, NULL); is_elfclass64 = (elf_ident[EI_CLASS] == ELFCLASS64); /* get the ELF header */ if (is_elfclass64) { ehdr = elf64_getehdr(elf); } else { ehdr = elf32_getehdr(elf); } if (ehdr == NULL) { failure(); } /* get the ELF section descriptor */ if (is_elfclass64) { scn = elf_getscn(elf, ((Elf64_Ehdr *) ehdr)->e_shstrndx); } else { scn = elf_getscn(elf, ((Elf32_Ehdr *) ehdr)->e_shstrndx); } if (scn == NULL) { failure(); } /* get the section header string table */ shstrtab = elf_getdata(scn, NULL); if (shstrtab == NULL) { failure(); } fix_count = 0; /* traverse the sections of the input file */ for (i = 1, scn = NULL; scn = elf_nextscn(elf, scn); i++) { int has_flag_set; /* is SHF_ALLOC flag set? */ int is_empty; /* is section empty? */ char * name; /* short hand pointer */ /* get the section header */ if (is_elfclass64) { shdr = elf64_getshdr(scn); } else { shdr = elf32_getshdr(scn); } if (shdr == NULL) { failure(); } if (is_elfclass64) { name = (char *)shstrtab->d_buf + ((Elf64_Shdr *) shdr)->sh_name; } else { name = (char *)shstrtab->d_buf + ((Elf32_Shdr *) shdr)->sh_name; } if (is_elfclass64) { has_flag_set = ((Elf64_Shdr *) shdr)->sh_flags & SHF_ALLOC; is_empty = ((Elf64_Shdr *) shdr)->sh_addr == 0 && ((Elf64_Shdr *) shdr)->sh_size == 0; } else { has_flag_set = ((Elf32_Shdr *) shdr)->sh_flags & SHF_ALLOC; is_empty = ((Elf32_Shdr *) shdr)->sh_addr == 0 && ((Elf32_Shdr *) shdr)->sh_size == 0; } if (is_empty && has_flag_set) { (void) printf("section[%u] '%s' is empty, " "but SHF_ALLOC flag is set.\n", i, name); (void) printf("Clearing the SHF_ALLOC flag.\n"); if (is_elfclass64) { ((Elf64_Shdr *) shdr)->sh_flags &= ~SHF_ALLOC; } else { ((Elf32_Shdr *) shdr)->sh_flags &= ~SHF_ALLOC; } fix_count++; } } /* end for each ELF section */ if (fix_count > 0) { (void) printf("Saving %d updates to '%s'\n", fix_count, elf_obj); (void) fflush(stdout); (void) elf_update(elf, ELF_C_NULL); /* recalc ELF memory structures */ (void) elf_update(elf, ELF_C_WRITE); /* write out changes to ELF obj */ } else { (void) printf("No SHF_ALLOC flags needed to be cleared.\n"); } (void) elf_end(elf); /* done with ELF obj */ (void) close(fd); (void) printf("Done %s '%s'\n", (fix_count > 0) ? "updating" : "with", elf_obj); (void) fflush(stdout); exit(0); } /* end main */ static void failure() { (void) fprintf(stderr, "%s\n", elf_errmsg(elf_errno())); exit(6); }