commit dcbc6b83eff5b9238170bdfed834ba934150895f

Author: Florian Weimer <fweimer@redhat.com>

Date:   Thu May 28 10:20:56 2020 +0200

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

    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>

diff --git a/elf/dl-hwcaps.c b/elf/dl-hwcaps.c

index ecf00b457760e517..ae2e4ca7fe91d407 100644

--- a/elf/dl-hwcaps.c

+++ b/elf/dl-hwcaps.c

@@ -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 "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)

       {