/* Hardware capability support for run-time dynamic loader.

   Copyright (C) 2012-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library 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; either

   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#include <assert.h>

#include <elf.h>

#include <errno.h>

#include <libintl.h>

#include <unistd.h>

#include <ldsodefs.h>

#include <dl-procinfo.h>

#include <dl-hwcaps.h>

#ifdef _DL_FIRST_PLATFORM

# define _DL_FIRST_EXTRA (_DL_FIRST_PLATFORM + _DL_PLATFORMS_COUNT)

#else

# define _DL_FIRST_EXTRA _DL_HWCAP_COUNT

#endif

/* Return an array of useful/necessary hardware capability names.  */

const struct r_strlenpair *

_dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,

		      size_t *max_capstrlen)

{

  uint64_t hwcap_mask = GET_HWCAP_MASK();

  /* Determine how many important bits are set.  */

  uint64_t masked = GLRO(dl_hwcap) & hwcap_mask;

  size_t cnt = platform != NULL;

  size_t n, m;

  size_t total;

  struct r_strlenpair *result;

  struct r_strlenpair *rp;

  char *cp;

  /* Count the number of bits set in the masked value.  */

  for (n = 0; (~((1ULL << n) - 1) & masked) != 0; ++n)

    if ((masked & (1ULL << n)) != 0)

      ++cnt;

#ifdef NEED_DL_SYSINFO_DSO

  /* The system-supplied DSO can contain a note of type 2, vendor "GNU".

     This gives us a list of names to treat as fake hwcap bits.  */

  const char *dsocaps = NULL;

  size_t dsocapslen = 0;

  if (GLRO(dl_sysinfo_map) != NULL)

    {

      const ElfW(Phdr) *const phdr = GLRO(dl_sysinfo_map)->l_phdr;

      const ElfW(Word) phnum = GLRO(dl_sysinfo_map)->l_phnum;

      for (uint_fast16_t i = 0; i < phnum; ++i)

	if (phdr[i].p_type == PT_NOTE)

	  {

	    const ElfW(Addr) start = (phdr[i].p_vaddr

				      + GLRO(dl_sysinfo_map)->l_addr);

	    /* NB: Some PT_NOTE segment may have alignment value of 0

	       or 1.  gABI specifies that PT_NOTE segments should be

	       aligned to 4 bytes in 32-bit objects and to 8 bytes in

	       64-bit objects.  As a Linux extension, we also support

	       4 byte alignment in 64-bit objects.  If p_align is less

	       than 4, we treate alignment as 4 bytes since some note

	       segments have 0 or 1 byte alignment.   */

	    ElfW(Addr) align = phdr[i].p_align;

	    if (align < 4)

	      align = 4;

	    else if (align != 4 && align != 8)

	      continue;

	    /* The standard ELF note layout is exactly as the anonymous struct.

	       The next element is a variable length vendor name of length

	       VENDORLEN (with a real length rounded to ElfW(Word)), followed

	       by the data of length DATALEN (with a real length rounded to

	       ElfW(Word)).  */

	    const struct

	    {

	      ElfW(Word) vendorlen;

	      ElfW(Word) datalen;

	      ElfW(Word) type;

	    } *note = (const void *) start;

	    while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)

	      {

		/* The layout of the type 2, vendor "GNU" note is as follows:

		   .long <Number of capabilities enabled by this note>

		   .long <Capabilities mask> (as mask >> _DL_FIRST_EXTRA).

		   .byte <The bit number for the next capability>

		   .asciz <The name of the capability>.  */

		if (note->type == NT_GNU_HWCAP

		    && note->vendorlen == sizeof "GNU"

		    && !memcmp ((note + 1), "GNU", sizeof "GNU")

		    && note->datalen > 2 * sizeof (ElfW(Word)) + 2)

		  {

		    const ElfW(Word) *p

		      = ((const void *) note

			 + ELF_NOTE_DESC_OFFSET (sizeof "GNU", align));

		    cnt += *p++;

		    ++p;	/* Skip mask word.  */

		    dsocaps = (const char *) p; /* Pseudo-string "name"  */

		    dsocapslen = note->datalen - sizeof *p * 2;

		    break;

		  }

		note = ((const void *) note

			+ ELF_NOTE_NEXT_OFFSET (note->vendorlen,

						note->datalen, align));

	      }

	    if (dsocaps != NULL)

	      break;

	  }

    }

#endif

  /* For TLS enabled builds always add 'tls'.  */

  ++cnt;

  /* Create temporary data structure to generate result table.  */

  struct r_strlenpair temp[cnt];

  m = 0;

#ifdef NEED_DL_SYSINFO_DSO

  if (dsocaps != NULL)

    {

      /* dsocaps points to the .asciz string, and -1 points to the mask

         .long just before the string.  */

      const ElfW(Word) mask = ((const ElfW(Word) *) dsocaps)[-1];

      GLRO(dl_hwcap) |= (uint64_t) mask << _DL_FIRST_EXTRA;

      /* Note that we add the dsocaps to the set already chosen by the

	 LD_HWCAP_MASK environment variable (or default HWCAP_IMPORTANT).

	 So there is no way to request ignoring an OS-supplied dsocap

	 string and bit like you can ignore an OS-supplied HWCAP bit.  */

      hwcap_mask |= (uint64_t) mask << _DL_FIRST_EXTRA;

#if HAVE_TUNABLES

      TUNABLE_SET (glibc, tune, hwcap_mask, uint64_t, hwcap_mask);

#else

      GLRO(dl_hwcap_mask) = hwcap_mask;

#endif

      size_t len;

      for (const char *p = dsocaps; p < dsocaps + dsocapslen; p += len + 1)

	{

	  uint_fast8_t bit = *p++;

	  len = strlen (p);

	  /* Skip entries that are not enabled in the mask word.  */

	  if (__glibc_likely (mask & ((ElfW(Word)) 1 << bit)))

	    {

	      temp[m].str = p;

	      temp[m].len = len;

	      ++m;

	    }

	  else

	    --cnt;

	}

    }

#endif

  for (n = 0; masked != 0; ++n)

    if ((masked & (1ULL << n)) != 0)

      {

	temp[m].str = _dl_hwcap_string (n);

	temp[m].len = strlen (temp[m].str);

	masked ^= 1ULL << n;

	++m;

      }

  if (platform != NULL)

    {

      temp[m].str = platform;

      temp[m].len = platform_len;

      ++m;

    }

  temp[m].str = "tls";

  temp[m].len = 3;

  ++m;

  assert (m == cnt);

  /* Determine the total size of all strings together.  */

  if (cnt == 1)

    total = temp[0].len + 1;

  else

    {

      total = temp[0].len + temp[cnt - 1].len + 2;

      if (cnt > 2)

	{

	  total <<= 1;

	  for (n = 1; n + 1 < cnt; ++n)

	    total += temp[n].len + 1;

	  if (cnt > 3

	      && (cnt >= sizeof (size_t) * 8

		  || total + (sizeof (*result) << 3)

		     >= (1UL << (sizeof (size_t) * 8 - cnt + 3))))

	    _dl_signal_error (ENOMEM, NULL, NULL,

			      N_("cannot create capability list"));

	  total <<= cnt - 3;

	}

    }

  /* The result structure: we use a very compressed way to store the

     various combinations of capability names.  */

  *sz = 1 << cnt;

  result = (struct r_strlenpair *) malloc (*sz * sizeof (*result) + total);

  if (result == NULL)

    _dl_signal_error (ENOMEM, NULL, NULL,

		      N_("cannot create capability list"));

  if (cnt == 1)

    {

      result[0].str = (char *) (result + *sz);

      result[0].len = temp[0].len + 1;

      result[1].str = (char *) (result + *sz);

      result[1].len = 0;

      cp = __mempcpy ((char *) (result + *sz), temp[0].str, temp[0].len);

      *cp = '/';

      *sz = 2;

      *max_capstrlen = result[0].len;

      return result;

    }

  /* Fill in the information.  This follows the following scheme

     (indices from TEMP for four strings):

	entry #0: 0, 1, 2, 3	binary: 1111

	      #1: 0, 1, 3		1101

	      #2: 0, 2, 3		1011

	      #3: 0, 3			1001

     This allows the representation of all possible combinations of

     capability names in the string.  First generate the strings.  */

  result[1].str = result[0].str = cp = (char *) (result + *sz);

#define add(idx) \

      cp = __mempcpy (__mempcpy (cp, temp[idx].str, temp[idx].len), "/", 1);

  if (cnt == 2)

    {

      add (1);

      add (0);

    }

  else

    {

      n = 1 << (cnt - 1);

      do

	{

	  n -= 2;

	  /* We always add the last string.  */

	  add (cnt - 1);

	  /* Add the strings which have the bit set in N.  */

	  for (m = cnt - 2; m > 0; --m)

	    if ((n & (1 << m)) != 0)

	      add (m);

	  /* Always add the first string.  */

	  add (0);

	}

      while (n != 0);

    }

#undef add

  /* Now we are ready to install the string pointers and length.  */

  for (n = 0; n < (1UL << cnt); ++n)

    result[n].len = 0;

  n = cnt;

  do

    {

      size_t mask = 1 << --n;

      rp = result;

      for (m = 1 << cnt; m > 0; ++rp)

	if ((--m & mask) != 0)

	  rp->len += temp[n].len + 1;

    }

  while (n != 0);

  /* The first half of the strings all include the first string.  */

  n = (1 << cnt) - 2;

  rp = &result[2];

  while (n != (1UL << (cnt - 1)))

    {

      if ((--n & 1) != 0)

	rp[0].str = rp[-2].str + rp[-2].len;

      else

	rp[0].str = rp[-1].str;

      ++rp;

    }

  /* The second half starts right after the first part of the string of

     the corresponding entry in the first half.  */

  do

    {

      rp[0].str = rp[-(1 << (cnt - 1))].str + temp[cnt - 1].len + 1;

      ++rp;

    }

  while (--n != 0);

  /* The maximum string length.  */

  *max_capstrlen = result[0].len;

  return result;

}