elf_clib.c

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/*
 * Copyright (c) 2015 Cisco and/or its affiliates.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include <vppinfra/elf_clib.h>

#include <stdlib.h>
#include <fcntl.h>
#include <sys/stat.h>

typedef struct {
  char ** path;
} path_search_t;

always_inline void
path_search_free (path_search_t * p)
{
  uword i;
  for (i = 0; i < vec_len (p->path); i++)
    vec_free (p->path[i]);
  vec_free (p->path);
}

static char **
split_string (char * string, u8 delimiter)
{
  char ** result = 0;
  char * p, * start, * s;
  
  p = string;
  while (1)
    {
      start = p;
      while (*p != 0 && *p != delimiter)
        p++;
      s = 0;
      vec_add (s, start, p - start);
      vec_add1 (s, 0);
      vec_add1 (result, s);
      if (*p == 0)
        break;
      p++;
    }

  return result;
}

static int
file_exists_and_is_executable (char * dir, char * file)
{
  char * path = (char *) format (0, "%s/%s%c", dir, file, 0);
  struct stat s;
  uword yes;

  yes = (stat (path, &s) >= 0
         && S_ISREG (s.st_mode)
         && 0 != (s.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH)));

  vec_free (path);

  return yes;
}

static char *
path_search (char * file)
{
  path_search_t ps;
  uword i;
  char * result;

  /* Relative or absolute path. */
  if (file[0] == '.' || file[0] == '/')
    return file;

  ps.path = split_string (getenv ("PATH"), ':');

  for (i = 0; i < vec_len (ps.path); i++)
    if (file_exists_and_is_executable (ps.path[i], file))
      break;

  result = 0;
  if (i < vec_len (ps.path))
    result = (char *) format (0, "%s/%s%c", ps.path[i], file);

  path_search_free (&ps);

  return result;
}

static clib_error_t *
clib_elf_parse_file (clib_elf_main_t * cem,
                     char * file_name,
                     void * link_address)
{
  elf_main_t * em;
  elf_section_t * s;
  int fd;
  struct stat fd_stat;
  uword mmap_length = 0;
  void * data = 0;
  clib_error_t * error = 0;

  vec_add2 (cem->elf_mains, em, 1);

  fd = open (file_name, 0);
  if (fd < 0)
    {
      error = clib_error_return_unix (0, "open `%s'", file_name);
      goto done;
    }

  if (fstat (fd, &fd_stat) < 0)
    {
      error = clib_error_return_unix (0, "fstat `%s'", file_name);
      goto done;
    }
  mmap_length = fd_stat.st_size;

  data = mmap (0, mmap_length, PROT_READ, MAP_SHARED, fd, /* offset */ 0);
  if (~pointer_to_uword (data) == 0)
    {
      error = clib_error_return_unix (0, "mmap `%s'", file_name);
      goto done;
    }

  error = elf_parse (em, data, mmap_length);
  if (error)
    goto done;

  /* Look for CLIB special sections. */
  {
    char * section_name_start = CLIB_ELF_SECTION_ADD_PREFIX ();
    uword section_name_start_len = strlen (section_name_start);

    vec_foreach (s, em->sections)
      {
        u8 * name = elf_section_name (em, s);
        uword * p;
        clib_elf_section_t * vs;
        clib_elf_section_bounds_t * b;

        /* Section name must begin with CLIB_ELF_SECTION key. */
        if (memcmp (name, section_name_start, section_name_start_len))
          continue;

        name += section_name_start_len;
        p = hash_get_mem (cem->section_by_name, name);
        if (p)
          vs = vec_elt_at_index (cem->sections, p[0]);
        else
          {
            name = format (0, "%s%c", name, 0);
            if (! cem->section_by_name)
              cem->section_by_name = hash_create_string (0, sizeof (uword));
            hash_set_mem (cem->section_by_name, name, vec_len (cem->sections));
            vec_add2 (cem->sections, vs, 1);
            vs->name = name;
          }

        vec_add2 (vs->bounds, b, 1);
        b->lo = link_address + s->header.exec_address;
        b->hi = b->lo + s->header.file_size;
      }
  }

  /* Parse symbols for this file. */
  {
    elf_symbol_table_t * t;
    elf64_symbol_t * s;

    elf_parse_symbols (em);
    vec_foreach (t, em->symbol_tables)
      {
        vec_foreach (s, t->symbols)
          {
            s->value += pointer_to_uword (link_address);
          }
      }
  }

  /* No need to keep section contents around. */
  {
    elf_section_t * s;
    vec_foreach (s, em->sections)
      {
        if (s->header.type != ELF_SECTION_STRING_TABLE)
          vec_free (s->contents);
      }
  }

 done:
  if (error)
    elf_main_free (em);
  if (fd >= 0)
    close (fd);
  if (data)
    munmap (data, mmap_length);
  return error;
}

#define __USE_GNU
#include <link.h>

static int
add_section (struct dl_phdr_info * info, size_t size, void * opaque)
{
  clib_elf_main_t * cem = opaque;
  clib_error_t * error;
  char * name = (char *) info->dlpi_name;
  void * addr = (void *) info->dlpi_addr;
  uword is_main;

  is_main = strlen (name) == 0;
  if (is_main)
    {
      static int done;

      /* Only do main program once. */
      if (done++)
        return 0;

      name = path_search (cem->exec_path);
      if (! name)
        clib_error ("failed to find %s on PATH", cem->exec_path);
      addr = 0;
    }

  error = clib_elf_parse_file (cem, name, addr);
  if (error)
    clib_error_report (error);

  if (is_main && name != cem->exec_path)
    vec_free (name);

  return 0;
}

static clib_elf_main_t clib_elf_main;

void clib_elf_main_init (char * exec_path)
{
  clib_elf_main_t * cem = &clib_elf_main;

  cem->exec_path = exec_path;

  dl_iterate_phdr (add_section, cem);
}

clib_elf_section_bounds_t *
clib_elf_get_section_bounds (char * name)
{
  clib_elf_main_t * em = &clib_elf_main;
  uword * p = hash_get (em->section_by_name, name);
  return p ? vec_elt_at_index (em->sections, p[0])->bounds : 0;
}

static uword
symbol_by_address_or_name (char * by_name,
                           uword by_address,
                           clib_elf_symbol_t * s)
{
  clib_elf_main_t * cem = &clib_elf_main;
  elf_main_t * em;

  vec_foreach (em, cem->elf_mains)
    {
      elf_symbol_table_t * t;
      s->elf_main_index = em - cem->elf_mains;
      vec_foreach (t, em->symbol_tables)
        {
          s->symbol_table_index = t - em->symbol_tables;
          if (by_name)
            {
              uword * p = hash_get (t->symbol_by_name, by_name);
              if (p)
                {
                  s->symbol = vec_elt (t->symbols, p[0]);
                  return 1;
                }
            }
          else
            {
              elf64_symbol_t * x;
              /* FIXME linear search. */
              vec_foreach (x, t->symbols)
                {
                  if (by_address >= x->value && by_address < x->value + x->size)
                    {
                      s->symbol = x[0];
                      return 1;
                    }
                }
            }
        }
    }

  return 0;
}

uword clib_elf_symbol_by_name (char * by_name, clib_elf_symbol_t * s)
{ return symbol_by_address_or_name (by_name, /* by_address */ 0, s); }

uword clib_elf_symbol_by_address (uword by_address, clib_elf_symbol_t * s)
{ return symbol_by_address_or_name (/* by_name */ 0, by_address, s); }

u8 * format_clib_elf_symbol (u8 * s, va_list * args)
{
  clib_elf_main_t * cem = &clib_elf_main;
  clib_elf_symbol_t * sym = va_arg (*args, clib_elf_symbol_t *);
  elf_main_t * em;
  elf_symbol_table_t * t;

  if (! sym)
    /* Just print table headings. */
    return format (s, "%U", format_elf_symbol, 0, 0, 0);

  else
    {
      em = vec_elt_at_index (cem->elf_mains, sym->elf_main_index);
      t = vec_elt_at_index (em->symbol_tables, sym->symbol_table_index);
      return format (s, "%U", format_elf_symbol, em, t, &sym->symbol);
    }
}

u8 * format_clib_elf_symbol_with_address (u8 * s, va_list * args)
{
  uword address = va_arg (*args, uword);
  clib_elf_main_t * cem = &clib_elf_main;
  clib_elf_symbol_t sym;
  elf_main_t * em;
  elf_symbol_table_t * t;

  if (clib_elf_symbol_by_address (address, &sym))
    {
      em = vec_elt_at_index (cem->elf_mains, sym.elf_main_index);
      t = vec_elt_at_index (em->symbol_tables, sym.symbol_table_index);
      s = format (s, "%s + 0x%wx",
                  elf_symbol_name (t, &sym.symbol),
                  address - sym.symbol.value);
    }
  else
    s = format (s, "0x%wx", address);

  return s;
}