1 /*

     2  * Copyright (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    12  * version 2 for more details (a copy is included in the LICENSE file that

    13  * accompanied this code).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  *

    23  */

    24 

    25 #include <unistd.h>

    26 #include <search.h>

    27 #include <stdlib.h>

    28 #include <string.h>

    29 #include <db.h>

    30 #include <fcntl.h>

    31 #include "symtab.h"

    32 #include "salibelf.h"

    33 

    34 

    35 // ----------------------------------------------------

    36 // functions for symbol lookups

    37 // ----------------------------------------------------

    38 

    39 struct elf_section {

    40   ELF_SHDR   *c_shdr;

    41   void       *c_data;

    42 };

    43 

    44 struct elf_symbol {

    45   char *name;

    46   uintptr_t offset;

    47   uintptr_t size;

    48 };

    49 

    50 typedef struct symtab {

    51   char *strs;

    52   size_t num_symbols;

    53   struct elf_symbol *symbols;

    54   DB* hash_table;

    55 } symtab_t;

    56 

    57 // read symbol table from given fd.

    58 struct symtab* build_symtab(int fd) {

    59   ELF_EHDR ehdr;

    60   struct symtab* symtab = NULL;

    61 

    62   // Reading of elf header

    63   struct elf_section *scn_cache = NULL;

    64   int cnt = 0;

    65   ELF_SHDR* shbuf = NULL;

    66   ELF_SHDR* cursct = NULL;

    67   ELF_PHDR* phbuf = NULL;

    68   int symtab_found = 0;

    69   int dynsym_found = 0;

    70   uint32_t symsection = SHT_SYMTAB;

    71 

    72   uintptr_t baseaddr = (uintptr_t)-1;

    73 

    74   lseek(fd, (off_t)0L, SEEK_SET);

    75   if (! read_elf_header(fd, &ehdr)) {

    76     // not an elf

    77     return NULL;

    78   }

    79 

    80   // read ELF header

    81   if ((shbuf = read_section_header_table(fd, &ehdr)) == NULL) {

    82     goto quit;

    83   }

    84 

    85   baseaddr = find_base_address(fd, &ehdr);

    86 

    87   scn_cache = calloc(ehdr.e_shnum, sizeof(*scn_cache));

    88   if (scn_cache == NULL) {

    89     goto quit;

    90   }

    91 

    92   for (cursct = shbuf, cnt = 0; cnt < ehdr.e_shnum; cnt++) {

    93     scn_cache[cnt].c_shdr = cursct;

    94     if (cursct->sh_type == SHT_SYMTAB ||

    95         cursct->sh_type == SHT_STRTAB ||

    96         cursct->sh_type == SHT_DYNSYM) {

    97       if ( (scn_cache[cnt].c_data = read_section_data(fd, &ehdr, cursct)) == NULL) {

    98          goto quit;

    99       }

   100     }

   101 

   102     if (cursct->sh_type == SHT_SYMTAB)

   103        symtab_found++;

   104 

   105     if (cursct->sh_type == SHT_DYNSYM)

   106        dynsym_found++;

   107 

   108     cursct++;

   109   }

   110 

   111   if (!symtab_found && dynsym_found)

   112      symsection = SHT_DYNSYM;

   113 

   114   for (cnt = 1; cnt < ehdr.e_shnum; cnt++) {

   115     ELF_SHDR *shdr = scn_cache[cnt].c_shdr;

   116 

   117     if (shdr->sh_type == symsection) {

   118       ELF_SYM  *syms;

   119       int j, n, rslt;

   120       size_t size;

   121 

   122       // FIXME: there could be multiple data buffers associated with the

   123       // same ELF section. Here we can handle only one buffer. See man page

   124       // for elf_getdata on Solaris.

   125 

   126       // guarantee(symtab == NULL, "multiple symtab");

   127       symtab = calloc(1, sizeof(*symtab));

   128       if (symtab == NULL) {

   129          goto quit;

   130       }

   131       // the symbol table

   132       syms = (ELF_SYM *)scn_cache[cnt].c_data;

   133 

   134       // number of symbols

   135       n = shdr->sh_size / shdr->sh_entsize;

   136 

   137       // create hash table, we use berkeley db to

   138       // manipulate the hash table.

   139       symtab->hash_table = dbopen(NULL, O_CREAT | O_RDWR, 0600, DB_HASH, NULL);

   140       // guarantee(symtab->hash_table, "unexpected failure: dbopen");

   141 

   142       // shdr->sh_link points to the section that contains the actual strings

   143       // for symbol names. the st_name field in ELF_SYM is just the

   144       // string table index. we make a copy of the string table so the

   145       // strings will not be destroyed by elf_end.

   146       size = scn_cache[shdr->sh_link].c_shdr->sh_size;

   147       symtab->strs = malloc(size);

   148       memcpy(symtab->strs, scn_cache[shdr->sh_link].c_data, size);

   149 

   150       // allocate memory for storing symbol offset and size;

   151       symtab->num_symbols = n;

   152       symtab->symbols = calloc(n , sizeof(*symtab->symbols));

   153 

   154       // copy symbols info our symtab and enter them info the hash table

   155       for (j = 0; j < n; j++, syms++) {

   156         DBT key, value;

   157         char *sym_name = symtab->strs + syms->st_name;

   158 

   159         // skip non-object and non-function symbols

   160         int st_type = ELF_ST_TYPE(syms->st_info);

   161         if ( st_type != STT_FUNC && st_type != STT_OBJECT)

   162            continue;

   163         // skip empty strings and undefined symbols

   164         if (*sym_name == '\0' || syms->st_shndx == SHN_UNDEF) continue;

   165 

   166         symtab->symbols[j].name   = sym_name;

   167         symtab->symbols[j].offset = syms->st_value - baseaddr;

   168         symtab->symbols[j].size   = syms->st_size;

   169 

   170         key.data = sym_name;

   171         key.size = strlen(sym_name) + 1;

   172         value.data = &(symtab->symbols[j]);

   173         value.size = sizeof(void *);

   174         (*symtab->hash_table->put)(symtab->hash_table, &key, &value, 0);

   175       }

   176     }

   177   }

   178 

   179 quit:

   180   if (shbuf) free(shbuf);

   181   if (phbuf) free(phbuf);

   182   if (scn_cache) {

   183     for (cnt = 0; cnt < ehdr.e_shnum; cnt++) {

   184       if (scn_cache[cnt].c_data != NULL) {

   185         free(scn_cache[cnt].c_data);

   186       }

   187     }

   188     free(scn_cache);

   189   }

   190   return symtab;

   191 }

   192 

   193 void destroy_symtab(struct symtab* symtab) {

   194   if (!symtab) return;

   195   if (symtab->strs) free(symtab->strs);

   196   if (symtab->symbols) free(symtab->symbols);

   197   if (symtab->hash_table) {

   198     symtab->hash_table->close(symtab->hash_table);

   199   }

   200   free(symtab);

   201 }

   202 

   203 uintptr_t search_symbol(struct symtab* symtab, uintptr_t base,

   204                       const char *sym_name, int *sym_size) {

   205   DBT key, value;

   206   int ret;

   207 

   208   // library does not have symbol table

   209   if (!symtab || !symtab->hash_table)

   210      return 0;

   211 

   212   key.data = (char*)(uintptr_t)sym_name;

   213   key.size = strlen(sym_name) + 1;

   214   ret = (*symtab->hash_table->get)(symtab->hash_table, &key, &value, 0);

   215   if (ret == 0) {

   216     struct elf_symbol *sym = value.data;

   217     uintptr_t rslt = (uintptr_t) ((char*)base + sym->offset);

   218     if (sym_size) *sym_size = sym->size;

   219     return rslt;

   220   }

   221 

   222 quit:

   223   return 0;

   224 }

   225 

   226 const char* nearest_symbol(struct symtab* symtab, uintptr_t offset,

   227                            uintptr_t* poffset) {

   228   int n = 0;

   229   if (!symtab) return NULL;

   230   for (; n < symtab->num_symbols; n++) {

   231      struct elf_symbol* sym = &(symtab->symbols[n]);

   232      if (sym->name != NULL &&

   233          offset >= sym->offset && offset < sym->offset + sym->size) {

   234         if (poffset) *poffset = (offset - sym->offset);

   235         return sym->name;

   236      }

   237   }

   238   return NULL;

   239 }