1  /*-
  2   * Copyright (c) 2006,2008 Joseph Koshy
  3   * All rights reserved.
  4   *
  5   * Redistribution and use in source and binary forms, with or without
  6   * modification, are permitted provided that the following conditions
  7   * are met:
  8   * 1. Redistributions of source code must retain the above copyright
  9   *    notice, this list of conditions and the following disclaimer.
 10   * 2. Redistributions in binary form must reproduce the above copyright
 11   *    notice, this list of conditions and the following disclaimer in the
 12   *    documentation and/or other materials provided with the distribution.
 13   *
 14   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 15   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 16   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 17   * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 18   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 19   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 20   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 21   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 22   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 23   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 24   * SUCH DAMAGE.
 25   */
 26  
 27  #include <sys/param.h>
 28  
 29  #include <assert.h>
 30  #include <gelf.h>
 31  
 32  #include "_libelf.h"
 33  
 34  #ifndef roundup2
 35  #define	roundup2(x, y)	(((x)+((y)-1))&(~((y)-1))) /* if y is powers of two */
 36  #endif
 37  
 38  ELFTC_VCSID("$Id$");
 39  
 40  /*
 41   * Convert an ELF section#,offset pair to a string pointer.
 42   */
 43  
 44  char *
 45  elf_strptr(Elf *e, size_t scndx, size_t offset)
 46  {
 47  	Elf_Scn *s;
 48  	Elf_Data *d;
 49  	GElf_Shdr shdr;
 50  	uint64_t alignment, count;
 51  
 52  	if (e == NULL || e->e_kind != ELF_K_ELF) {
 53  		LIBELF_SET_ERROR(ARGUMENT, 0);
 54  		return (NULL);
 55  	}
 56  
 57  	if ((s = elf_getscn(e, scndx)) == NULL ||
 58  	    gelf_getshdr(s, &shdr) == NULL)
 59  		return (NULL);
 60  
 61  	if (shdr.sh_type != SHT_STRTAB ||
 62  	    offset >= shdr.sh_size) {
 63  		LIBELF_SET_ERROR(ARGUMENT, 0);
 64  		return (NULL);
 65  	}
 66  
 67  	d = NULL;
 68  	if (e->e_flags & ELF_F_LAYOUT) {
 69  
 70  		/*
 71  		 * The application is taking responsibility for the
 72  		 * ELF object's layout, so we can directly translate
 73  		 * an offset to a `char *' address using the `d_off'
 74  		 * members of Elf_Data descriptors.
 75  		 */
 76  		while ((d = elf_getdata(s, d)) != NULL) {
 77  
 78  			if (d->d_buf == 0 || d->d_size == 0)
 79  				continue;
 80  
 81  			if (d->d_type != ELF_T_BYTE) {
 82  				LIBELF_SET_ERROR(DATA, 0);
 83  				return (NULL);
 84  			}
 85  
 86  			if (offset >= d->d_off &&
 87  			    offset < d->d_off + d->d_size)
 88  				return ((char *) d->d_buf + offset - d->d_off);
 89  		}
 90  	} else {
 91  		/*
 92  		 * Otherwise, the `d_off' members are not useable and
 93  		 * we need to compute offsets ourselves, taking into
 94  		 * account 'holes' in coverage of the section introduced
 95  		 * by alignment requirements.
 96  		 */
 97  		count = (uint64_t) 0;	/* cumulative count of bytes seen */
 98  		while ((d = elf_getdata(s, d)) != NULL && count <= offset) {
 99  
100  			if (d->d_buf == NULL || d->d_size == 0)
101  				continue;
102  
103  			if (d->d_type != ELF_T_BYTE) {
104  				LIBELF_SET_ERROR(DATA, 0);
105  				return (NULL);
106  			}
107  
108  			if ((alignment = d->d_align) > 1) {
109  				if ((alignment & (alignment - 1)) != 0) {
110  					LIBELF_SET_ERROR(DATA, 0);
111  					return (NULL);
112  				}
113  				count = roundup2(count, alignment);
114  			}
115  
116  			if (offset < count) {
117  				/* offset starts in the 'hole' */
118  				LIBELF_SET_ERROR(ARGUMENT, 0);
119  				return (NULL);
120  			}
121  
122  			if (offset < count + d->d_size) {
123  				if (d->d_buf != NULL)
124  					return ((char *) d->d_buf +
125  					    offset - count);
126  				LIBELF_SET_ERROR(DATA, 0);
127  				return (NULL);
128  			}
129  
130  			count += d->d_size;
131  		}
132  	}
133  
134  	LIBELF_SET_ERROR(ARGUMENT, 0);
135  	return (NULL);
136  }