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glibc/elf/dl-hwcaps.c

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/* Hardware capability support for run-time dynamic loader.
Copyright (C) 2012-2017 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);
/* 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)
{
#define ROUND(len) (((len) + sizeof (ElfW(Word)) - 1) & -sizeof (ElfW(Word)))
/* 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 + 1)
+ ROUND (sizeof "GNU"));
cnt += *p++;
++p; /* Skip mask word. */
dsocaps = (const char *) p; /* Pseudo-string "<b>name" */
dsocapslen = note->datalen - sizeof *p * 2;
break;
}
note = ((const void *) (note + 1)
+ ROUND (note->vendorlen) + ROUND (note->datalen));
#undef ROUND
}
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;
}
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