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

[Florian Weimer]

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.

---
 elf/dl-hwcaps.c | 110 --------------------------------------------------------
 1 file changed, 110 deletions(-)

diff --git a/elf/dl-hwcaps.c b/elf/dl-hwcaps.c
index 71aea86700..6df9efb255 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 "<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)
       {