elf_ops.c

/*
This file is part of GOTCHA.  For copyright information see the COPYRIGHT
file in the top level directory, or at
https://github.com/LLNL/gotcha/blob/master/COPYRIGHT
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License (as published by the Free
Software Foundation) version 2.1 dated February 1999.  This program 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 terms and conditions of the GNU Lesser General Public License
for more details.  You should have received a copy of the GNU Lesser General
Public License along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/

#include "elf_ops.h"
#include "libc_wrappers.h"
#include <elf.h>
struct gnu_hash_header {
   uint32_t nbuckets;   //!< The number of buckets to hash symbols into
   uint32_t symndx;     //!< Index of the first symbol accessible via hashtable in the symbol table
   uint32_t maskwords;  //!< Number of words in the hash table's bloom filter
   uint32_t shift2;     //!< The bloom filter's shift count
};

static uint32_t gnu_hash_func(const char *str) {
  uint32_t hash = 5381;
  for (; *str != '\0'; str++) {
    hash = hash * 33 + *str;
  }
  return hash;
}

signed long lookup_gnu_hash_symbol(const char *name, ElfW(Sym) * syms,
                                   char *symnames,
                                   void *sheader) {
  uint32_t *buckets, *vals;
  uint32_t hash_val;
  uint32_t cur_sym, cur_sym_hashval;
  struct gnu_hash_header *header = (struct gnu_hash_header *) (sheader);

  buckets = (uint32_t *)(((unsigned char *)(header + 1)) +
                         (header->maskwords * sizeof(ElfW(Addr))));
  vals = buckets + header->nbuckets;

  hash_val = gnu_hash_func(name);
  cur_sym = buckets[hash_val % header->nbuckets];
  if (cur_sym == 0) {
    return -1;
  }

  hash_val &= ~1;
  for (;;) {
    cur_sym_hashval = vals[cur_sym - header->symndx];
    if (((cur_sym_hashval & ~1) == hash_val) &&
        (gotcha_strcmp(name, symnames + syms[cur_sym].st_name) == 0)) {
      return (signed long)cur_sym;
    }
    if (cur_sym_hashval & 1) {
      return -1;
    }
    cur_sym++;
  }
}

static unsigned long elf_hash(const unsigned char *name) {
  unsigned int h = 0, g;
  while (*name != '\0') {
    h = (h << 4) + *name++;
    if ((g = h & 0xf0000000)) {
      h ^= g >> 24;
    }
    h &= ~g;
  }
  return h;
}

signed long lookup_elf_hash_symbol(const char *name, ElfW(Sym) * syms,
                                   char *symnames, ElfW(Word) * header) {
  ElfW(Word) *nbucket = header + 0;
  ElfW(Word) *buckets = header + 2;
  ElfW(Word) *chains = buckets + *nbucket;

  unsigned int x = elf_hash((const unsigned char *)name);
  signed long y = (signed long)buckets[x % *nbucket];
  while (y != STN_UNDEF) {
    if (gotcha_strcmp(name, symnames + syms[y].st_name) == 0) {
      return y;
    }
    y = chains[y];
  }

  return -1;
}