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elf: Do not read hwcaps from the vDSO in ld.so

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This was only ever used for the "nosegneg" flag.  This approach for
passing hardware capability information creates a subtle dependency
between the kernel and userspace, and ld.so.cache contents.  It seems
inappropriate for toady, where people expect to be able to run
system images which very different kernel versions.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
This commit is contained in:
Florian Weimer 2020-05-28 10:20:56 +02:00
parent ef3330fde4
commit dcbc6b83ef
1 changed files with 0 additions and 110 deletions
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110
elf/dl-hwcaps.c
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@ -26,12 +26,6 @@
#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,
@ -52,116 +46,12 @@ _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
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 "<b>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, cpu, 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)
{