path: root/gdb/auxv.c

/* Auxiliary vector support for GDB, the GNU debugger.

   Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010
   Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   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
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"
#include "target.h"
#include "gdbtypes.h"
#include "command.h"
#include "inferior.h"
#include "valprint.h"
#include "gdb_assert.h"
#include "gdbcore.h"

#include "auxv.h"
#include "elf/common.h"

#include <unistd.h>
#include <fcntl.h>


/* This function handles access via /proc/PID/auxv, which is a common method
   for native targets.  */

static LONGEST
procfs_xfer_auxv (gdb_byte *readbuf,
		  const gdb_byte *writebuf,
		  ULONGEST offset,
		  LONGEST len)
{
  char *pathname;
  int fd;
  LONGEST n;

  pathname = xstrprintf ("/proc/%d/auxv", PIDGET (inferior_ptid));
  fd = open (pathname, writebuf != NULL ? O_WRONLY : O_RDONLY);
  xfree (pathname);
  if (fd < 0)
    return -1;

  if (offset != (ULONGEST) 0
      && lseek (fd, (off_t) offset, SEEK_SET) != (off_t) offset)
    n = -1;
  else if (readbuf != NULL)
    n = read (fd, readbuf, len);
  else
    n = write (fd, writebuf, len);

  (void) close (fd);

  return n;
}

/* This function handles access via ld.so's symbol `_dl_auxv'.  */

static LONGEST
ld_so_xfer_auxv (gdb_byte *readbuf,
		 const gdb_byte *writebuf,
		 ULONGEST offset,
		 LONGEST len)
{
  struct minimal_symbol *msym;
  CORE_ADDR data_address, pointer_address;
  struct type *ptr_type = builtin_type (target_gdbarch)->builtin_data_ptr;
  size_t ptr_size = TYPE_LENGTH (ptr_type);
  size_t auxv_pair_size = 2 * ptr_size;
  gdb_byte *ptr_buf = alloca (ptr_size);
  LONGEST retval;
  size_t block;

  msym = lookup_minimal_symbol ("_dl_auxv", NULL, NULL);
  if (msym == NULL)
    return -1;

  if (MSYMBOL_SIZE (msym) != ptr_size)
    return -1;

  /* POINTER_ADDRESS is a location where the `_dl_auxv' variable resides.
     DATA_ADDRESS is the inferior value present in `_dl_auxv', therefore the
     real inferior AUXV address.  */

  pointer_address = SYMBOL_VALUE_ADDRESS (msym);

  /* The location of the _dl_auxv symbol may no longer be correct if
     ld.so runs at a different address than the one present in the file.
     This is very common case - for unprelinked ld.so or with a PIE executable.
     PIE executable forces random address even for libraries already being
     prelinked to some address.  PIE executables themselves are never prelinked
     even on prelinked systems.  Prelinking of a PIE executable would block
     their purpose of randomizing load of everything including the executable.

     If the memory read fails, return -1 to fallback on another mechanism for
     retrieving the AUXV.

     In most cases of a PIE running under valgrind there is no way to find
     out the base addresses of any of ld.so, executable or AUXV as everything
     is randomized and /proc information is not relevant for the virtual
     executable running under valgrind.  We think that we might need a valgrind
     extension to make it work.  This is PR 11440.  */

  if (target_read_memory (pointer_address, ptr_buf, ptr_size) != 0)
    return -1;

  data_address = extract_typed_address (ptr_buf, ptr_type);

  /* Possibly still not initialized such as during an inferior startup.  */
  if (data_address == 0)
    return -1;

  data_address += offset;

  if (writebuf != NULL)
    {
      if (target_write_memory (data_address, writebuf, len) == 0)
	return len;
      else
	return -1;
    }

  /* Stop if trying to read past the existing AUXV block.  The final AT_NULL
     was already returned before.  */

  if (offset >= auxv_pair_size)
    {
      if (target_read_memory (data_address - auxv_pair_size, ptr_buf,
			      ptr_size) != 0)
	return -1;

      if (extract_typed_address (ptr_buf, ptr_type) == AT_NULL)
	return 0;
    }

  retval = 0;
  block = 0x400;
  gdb_assert (block % auxv_pair_size == 0);

  while (len > 0)
    {
      if (block > len)
	block = len;

      /* Reading sizes smaller than AUXV_PAIR_SIZE is not supported.  Tails
	 unaligned to AUXV_PAIR_SIZE will not be read during a call (they
	 should be completed during next read with new/extended buffer).  */

      block &= -auxv_pair_size;
      if (block == 0)
	return retval;

      if (target_read_memory (data_address, readbuf, block) != 0)
	{
	  if (block <= auxv_pair_size)
	    return retval;

	  block = auxv_pair_size;
	  continue;
	}

      data_address += block;
      len -= block;

      /* Check terminal AT_NULL.  This function is being called indefinitely
         being extended its READBUF until it returns EOF (0).  */

      while (block >= auxv_pair_size)
	{
	  retval += auxv_pair_size;

	  if (extract_typed_address (readbuf, ptr_type) == AT_NULL)
	    return retval;

	  readbuf += auxv_pair_size;
	  block -= auxv_pair_size;
	}
    }

  return retval;
}

/* This function is called like a to_xfer_partial hook, but must be
   called with TARGET_OBJECT_AUXV.  It handles access to AUXV.  */

LONGEST
memory_xfer_auxv (struct target_ops *ops,
		  enum target_object object,
		  const char *annex,
		  gdb_byte *readbuf,
		  const gdb_byte *writebuf,
		  ULONGEST offset,
		  LONGEST len)
{
  gdb_assert (object == TARGET_OBJECT_AUXV);
  gdb_assert (readbuf || writebuf);

   /* ld_so_xfer_auxv is the only function safe for virtual executables being
      executed by valgrind's memcheck.  Using ld_so_xfer_auxv during inferior
      startup is problematic, because ld.so symbol tables have not yet been
      relocated.  So GDB uses this function only when attaching to a process.
      */

  if (current_inferior ()->attach_flag != 0)
    {
      LONGEST retval;

      retval = ld_so_xfer_auxv (readbuf, writebuf, offset, len);
      if (retval != -1)
	return retval;
    }

  return procfs_xfer_auxv (readbuf, writebuf, offset, len);
}

/* Read one auxv entry from *READPTR, not reading locations >= ENDPTR.
   Return 0 if *READPTR is already at the end of the buffer.
   Return -1 if there is insufficient buffer for a whole entry.
   Return 1 if an entry was read into *TYPEP and *VALP.  */
static int
default_auxv_parse (struct target_ops *ops, gdb_byte **readptr,
		   gdb_byte *endptr, CORE_ADDR *typep, CORE_ADDR *valp)
{
  const int sizeof_auxv_field = gdbarch_ptr_bit (target_gdbarch)
				/ TARGET_CHAR_BIT;
  const enum bfd_endian byte_order = gdbarch_byte_order (target_gdbarch);
  gdb_byte *ptr = *readptr;

  if (endptr == ptr)
    return 0;

  if (endptr - ptr < sizeof_auxv_field * 2)
    return -1;

  *typep = extract_unsigned_integer (ptr, sizeof_auxv_field, byte_order);
  ptr += sizeof_auxv_field;
  *valp = extract_unsigned_integer (ptr, sizeof_auxv_field, byte_order);
  ptr += sizeof_auxv_field;

  *readptr = ptr;
  return 1;
}

/* Read one auxv entry from *READPTR, not reading locations >= ENDPTR.
   Return 0 if *READPTR is already at the end of the buffer.
   Return -1 if there is insufficient buffer for a whole entry.
   Return 1 if an entry was read into *TYPEP and *VALP.  */
int
target_auxv_parse (struct target_ops *ops, gdb_byte **readptr,
                  gdb_byte *endptr, CORE_ADDR *typep, CORE_ADDR *valp)
{
  struct target_ops *t;

  for (t = ops; t != NULL; t = t->beneath)
    if (t->to_auxv_parse != NULL)
      return t->to_auxv_parse (t, readptr, endptr, typep, valp);
  
  return default_auxv_parse (ops, readptr, endptr, typep, valp);
}

/* Extract the auxiliary vector entry with a_type matching MATCH.
   Return zero if no such entry was found, or -1 if there was
   an error getting the information.  On success, return 1 after
   storing the entry's value field in *VALP.  */
int
target_auxv_search (struct target_ops *ops, CORE_ADDR match, CORE_ADDR *valp)
{
  CORE_ADDR type, val;
  gdb_byte *data;
  LONGEST n = target_read_alloc (ops, TARGET_OBJECT_AUXV, NULL, &data);
  gdb_byte *ptr = data;

  if (n <= 0)
    return n;

  while (1)
    switch (target_auxv_parse (ops, &ptr, data + n, &type, &val))
      {
      case 1:			/* Here's an entry, check it.  */
	if (type == match)
	  {
	    xfree (data);
	    *valp = val;
	    return 1;
	  }
	break;
      case 0:			/* End of the vector.  */
	xfree (data);
	return 0;
      default:			/* Bogosity.  */
	xfree (data);
	return -1;
      }

  /*NOTREACHED*/
}


/* Print the contents of the target's AUXV on the specified file. */
int
fprint_target_auxv (struct ui_file *file, struct target_ops *ops)
{
  CORE_ADDR type, val;
  gdb_byte *data;
  LONGEST len = target_read_alloc (ops, TARGET_OBJECT_AUXV, NULL,
				   &data);
  gdb_byte *ptr = data;
  int ents = 0;

  if (len <= 0)
    return len;

  while (target_auxv_parse (ops, &ptr, data + len, &type, &val) > 0)
    {
      const char *name = "???";
      const char *description = "";
      enum { dec, hex, str } flavor = hex;

      switch (type)
	{
#define TAG(tag, text, kind) \
	case tag: name = #tag; description = text; flavor = kind; break
	  TAG (AT_NULL, _("End of vector"), hex);
	  TAG (AT_IGNORE, _("Entry should be ignored"), hex);
	  TAG (AT_EXECFD, _("File descriptor of program"), dec);
	  TAG (AT_PHDR, _("Program headers for program"), hex);
	  TAG (AT_PHENT, _("Size of program header entry"), dec);
	  TAG (AT_PHNUM, _("Number of program headers"), dec);
	  TAG (AT_PAGESZ, _("System page size"), dec);
	  TAG (AT_BASE, _("Base address of interpreter"), hex);
	  TAG (AT_FLAGS, _("Flags"), hex);
	  TAG (AT_ENTRY, _("Entry point of program"), hex);
	  TAG (AT_NOTELF, _("Program is not ELF"), dec);
	  TAG (AT_UID, _("Real user ID"), dec);
	  TAG (AT_EUID, _("Effective user ID"), dec);
	  TAG (AT_GID, _("Real group ID"), dec);
	  TAG (AT_EGID, _("Effective group ID"), dec);
	  TAG (AT_CLKTCK, _("Frequency of times()"), dec);
	  TAG (AT_PLATFORM, _("String identifying platform"), str);
	  TAG (AT_HWCAP, _("Machine-dependent CPU capability hints"), hex);
	  TAG (AT_FPUCW, _("Used FPU control word"), dec);
	  TAG (AT_DCACHEBSIZE, _("Data cache block size"), dec);
	  TAG (AT_ICACHEBSIZE, _("Instruction cache block size"), dec);
	  TAG (AT_UCACHEBSIZE, _("Unified cache block size"), dec);
	  TAG (AT_IGNOREPPC, _("Entry should be ignored"), dec);
	  TAG (AT_BASE_PLATFORM, _("String identifying base platform"), str);
	  TAG (AT_RANDOM, _("Address of 16 random bytes"), hex);
	  TAG (AT_EXECFN, _("File name of executable"), str);
	  TAG (AT_SECURE, _("Boolean, was exec setuid-like?"), dec);
	  TAG (AT_SYSINFO, _("Special system info/entry points"), hex);
	  TAG (AT_SYSINFO_EHDR, _("System-supplied DSO's ELF header"), hex);
	  TAG (AT_SUN_UID, _("Effective user ID"), dec);
	  TAG (AT_SUN_RUID, _("Real user ID"), dec);
	  TAG (AT_SUN_GID, _("Effective group ID"), dec);
	  TAG (AT_SUN_RGID, _("Real group ID"), dec);
	  TAG (AT_SUN_LDELF, _("Dynamic linker's ELF header"), hex);
	  TAG (AT_SUN_LDSHDR, _("Dynamic linker's section headers"), hex);
	  TAG (AT_SUN_LDNAME, _("String giving name of dynamic linker"), str);
	  TAG (AT_SUN_LPAGESZ, _("Large pagesize"), dec);
	  TAG (AT_SUN_PLATFORM, _("Platform name string"), str);
	  TAG (AT_SUN_HWCAP, _("Machine-dependent CPU capability hints"), hex);
	  TAG (AT_SUN_IFLUSH, _("Should flush icache?"), dec);
	  TAG (AT_SUN_CPU, _("CPU name string"), str);
	  TAG (AT_SUN_EMUL_ENTRY, _("COFF entry point address"), hex);
	  TAG (AT_SUN_EMUL_EXECFD, _("COFF executable file descriptor"), dec);
	  TAG (AT_SUN_EXECNAME,
	       _("Canonicalized file name given to execve"), str);
	  TAG (AT_SUN_MMU, _("String for name of MMU module"), str);
	  TAG (AT_SUN_LDDATA, _("Dynamic linker's data segment address"), hex);
	  TAG (AT_SUN_AUXFLAGS,
	       _("AF_SUN_ flags passed from the kernel"), hex);
	}

      fprintf_filtered (file, "%-4s %-20s %-30s ",
			plongest (type), name, description);
      switch (flavor)
	{
	case dec:
	  fprintf_filtered (file, "%s\n", plongest (val));
	  break;
	case hex:
	  fprintf_filtered (file, "%s\n", paddress (target_gdbarch, val));
	  break;
	case str:
	  {
	    struct value_print_options opts;

	    get_user_print_options (&opts);
	    if (opts.addressprint)
	      fprintf_filtered (file, "%s", paddress (target_gdbarch, val));
	    val_print_string (builtin_type (target_gdbarch)->builtin_char,
			      val, -1, file, &opts);
	    fprintf_filtered (file, "\n");
	  }
	  break;
	}
      ++ents;
      if (type == AT_NULL)
	break;
    }

  xfree (data);

  return ents;
}

static void
info_auxv_command (char *cmd, int from_tty)
{
  if (! target_has_stack)
    error (_("The program has no auxiliary information now."));
  else
    {
      int ents = fprint_target_auxv (gdb_stdout, &current_target);

      if (ents < 0)
	error (_("No auxiliary vector found, or failed reading it."));
      else if (ents == 0)
	error (_("Auxiliary vector is empty."));
    }
}


extern initialize_file_ftype _initialize_auxv; /* -Wmissing-prototypes; */

void
_initialize_auxv (void)
{
  add_info ("auxv", info_auxv_command,
	    _("Display the inferior's auxiliary vector.\n\
This is information provided by the operating system at program startup."));
}