ldconfig/x86: Store ISA level in cache and aux cache

Store ISA level in the portion of the unused upper 32 bits of the hwcaps
field in cache and the unused pad field in aux cache.  ISA level is stored
and checked only for shared objects in glibc-hwcaps subdirectories.  The
shared objects in the default directories aren't checked since there are
no fallbacks for these shared objects.

Tested on x86-64-v2, x86-64-v3 and x86-64-v4 machines with
--disable-hardcoded-path-in-tests and --enable-hardcoded-path-in-tests.

elf/cache.c

@@ -146,6 +146,7 @@ struct cache_entry
   struct stringtable_entry *path; /* Path to find library.  */
   int flags;			/* Flags to indicate kind of library.  */
   unsigned int osversion;	/* Required OS version.  */
+  unsigned int isa_level;	/* Required ISA level.  */
   uint64_t hwcap;		/* Important hardware capabilities.  */
   int bits_hwcap;		/* Number of bits set in hwcap.  */
 
@@ -549,6 +550,19 @@ write_extensions (int fd, uint32_t str_offset,
   free (ext);
 }
 
+/* Compute the hwcap value from ENTRY.  */
+static inline uint64_t
+compute_hwcap_value (struct cache_entry *entry)
+{
+  if (entry->isa_level > DL_CACHE_HWCAP_ISA_LEVEL_MASK)
+    error (EXIT_FAILURE, 0, _("%s: ISA level is too high (%d > %d)"),
+	   entry->path->string, entry->isa_level,
+	   DL_CACHE_HWCAP_ISA_LEVEL_MASK);
+  return (DL_CACHE_HWCAP_EXTENSION
+	  | (((uint64_t) entry->isa_level) << 32)
+	  | entry->hwcaps->section_index);
+}
+
 /* Save the contents of the cache.  */
 void
 save_cache (const char *cache_name)
@@ -662,7 +676,7 @@ save_cache (const char *cache_name)
 	    file_entries_new->libs[idx_new].hwcap = entry->hwcap;
 	  else
 	    file_entries_new->libs[idx_new].hwcap
-	      = DL_CACHE_HWCAP_EXTENSION | entry->hwcaps->section_index;
+	      = compute_hwcap_value (entry);
 	  file_entries_new->libs[idx_new].key
 	    = str_offset + entry->lib->offset;
 	  file_entries_new->libs[idx_new].value
@@ -777,7 +791,8 @@ save_cache (const char *cache_name)
 /* Add one library to the cache.  */
 void
 add_to_cache (const char *path, const char *filename, const char *soname,
-	      int flags, unsigned int osversion, uint64_t hwcap,
+	      int flags, unsigned int osversion,
+	      unsigned int isa_level, uint64_t hwcap,
 	      struct glibc_hwcaps_subdirectory *hwcaps)
 {
   struct cache_entry *new_entry = xmalloc (sizeof (*new_entry));
@@ -795,6 +810,7 @@ add_to_cache (const char *path, const char *filename, const char *soname,
   new_entry->path = path_interned;
   new_entry->flags = flags;
   new_entry->osversion = osversion;
+  new_entry->isa_level = isa_level;
   new_entry->hwcap = hwcap;
   new_entry->hwcaps = hwcaps;
   new_entry->bits_hwcap = 0;
@@ -851,6 +867,7 @@ struct aux_cache_entry
   struct aux_cache_entry_id id;
   int flags;
   unsigned int osversion;
+  unsigned int isa_level;
   int used;
   char *soname;
   struct aux_cache_entry *next;
@@ -864,7 +881,7 @@ struct aux_cache_file_entry
   int32_t flags;		/* This is 1 for an ELF library.  */
   uint32_t soname;		/* String table indice.  */
   uint32_t osversion;		/* Required OS version.	 */
-  int32_t pad;
+  uint32_t isa_level;		/* Required ISA level.	 */
 };
 
 /* ldconfig maintains an auxiliary cache file that allows
@@ -915,7 +932,8 @@ init_aux_cache (void)
 
 int
 search_aux_cache (struct stat64 *stat_buf, int *flags,
-		  unsigned int *osversion, char **soname)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  char **soname)
 {
   struct aux_cache_entry_id id;
   id.ino = (uint64_t) stat_buf->st_ino;
@@ -933,6 +951,7 @@ search_aux_cache (struct stat64 *stat_buf, int *flags,
       {
 	*flags = entry->flags;
 	*osversion = entry->osversion;
+	*isa_level = entry->isa_level;
 	if (entry->soname != NULL)
 	  *soname = xstrdup (entry->soname);
 	else
@@ -946,7 +965,8 @@ search_aux_cache (struct stat64 *stat_buf, int *flags,
 
 static void
 insert_to_aux_cache (struct aux_cache_entry_id *id, int flags,
-		     unsigned int osversion, const char *soname, int used)
+		     unsigned int osversion, unsigned int isa_level,
+		     const char *soname, int used)
 {
   size_t hash = aux_cache_entry_id_hash (id) % aux_hash_size;
   struct aux_cache_entry *entry;
@@ -962,6 +982,7 @@ insert_to_aux_cache (struct aux_cache_entry_id *id, int flags,
   entry->id = *id;
   entry->flags = flags;
   entry->osversion = osversion;
+  entry->isa_level = isa_level;
   entry->used = used;
   if (soname != NULL)
     entry->soname = memcpy ((char *) (entry + 1), soname, len);
@@ -973,14 +994,15 @@ insert_to_aux_cache (struct aux_cache_entry_id *id, int flags,
 
 void
 add_to_aux_cache (struct stat64 *stat_buf, int flags,
-		  unsigned int osversion, const char *soname)
+		  unsigned int osversion, unsigned int isa_level,
+		  const char *soname)
 {
   struct aux_cache_entry_id id;
   id.ino = (uint64_t) stat_buf->st_ino;
   id.ctime = (uint64_t) stat_buf->st_ctime;
   id.size = (uint64_t) stat_buf->st_size;
   id.dev = (uint64_t) stat_buf->st_dev;
-  insert_to_aux_cache (&id, flags, osversion, soname, 1);
+  insert_to_aux_cache (&id, flags, osversion, isa_level, soname, 1);
 }
 
 /* Load auxiliary cache to search for unchanged entries.   */
@@ -1026,6 +1048,7 @@ load_aux_cache (const char *aux_cache_name)
     insert_to_aux_cache (&aux_cache->libs[i].id,
 			 aux_cache->libs[i].flags,
 			 aux_cache->libs[i].osversion,
+			 aux_cache->libs[i].isa_level,
 			 aux_cache->libs[i].soname == 0
 			 ? NULL : aux_cache_data + aux_cache->libs[i].soname,
 			 0);
@@ -1094,7 +1117,7 @@ save_aux_cache (const char *aux_cache_name)
 	      str_offset += len;
 	    }
 	  file_entries->libs[idx].osversion = entry->osversion;
-	  file_entries->libs[idx++].pad = 0;
+	  file_entries->libs[idx++].isa_level = entry->isa_level;
 	}
 
   /* Write out auxiliary cache file.  */

elf/dl-cache.c

@@ -25,6 +25,7 @@
 #include <stdint.h>
 #include <_itoa.h>
 #include <dl-hwcaps.h>
+#include <dl-isa-level.h>
 
 #ifndef _DL_PLATFORMS_COUNT
 # define _DL_PLATFORMS_COUNT 0
@@ -284,6 +285,9 @@ search_cache (const char *string_table, uint32_t string_table_size,
 
 #ifdef SHARED
 			  named_hwcap = dl_cache_hwcap_extension (libnew);
+			  if (named_hwcap
+			      && !dl_cache_hwcap_isa_level_compatible (libnew))
+			    continue;
 #endif
 
 			  /* The entries with named/extension hwcaps

elf/ldconfig.c

@@ -655,6 +655,7 @@ manual_link (char *library)
   struct stat64 stat_buf;
   int flag;
   unsigned int osversion;
+  unsigned int isa_level;
 
   /* Prepare arguments for create_links call.  Split library name in
      directory and filename first.  Since path is allocated, we've got
@@ -721,7 +722,7 @@ manual_link (char *library)
     }
 
   if (process_file (real_library, library, libname, &flag, &osversion,
-		    &soname, 0, &stat_buf))
+		    &isa_level, &soname, 0, &stat_buf))
     {
       error (0, 0, _("No link created since soname could not be found for %s"),
 	     library);
@@ -768,6 +769,7 @@ struct dlib_entry
   int flag;
   int is_link;
   unsigned int osversion;
+  unsigned int isa_level;
   struct dlib_entry *next;
 };
 
@@ -980,17 +982,21 @@ search_dir (const struct dir_entry *entry)
 	 library already and it's not changed.  */
       char *soname;
       unsigned int osversion;
-      if (!search_aux_cache (&lstat_buf, &flag, &osversion, &soname))
+      unsigned int isa_level;
+      if (!search_aux_cache (&lstat_buf, &flag, &osversion, &isa_level,
+			     &soname))
 	{
 	  if (process_file (real_name, file_name, direntry->d_name, &flag,
-			    &osversion, &soname, is_link, &lstat_buf))
+			    &osversion, &isa_level, &soname, is_link,
+			    &lstat_buf))
 	    {
 	      if (real_name != real_file_name)
 		free (real_name);
 	      continue;
 	    }
 	  else if (opt_build_cache)
-	    add_to_aux_cache (&lstat_buf, flag, osversion, soname);
+	    add_to_aux_cache (&lstat_buf, flag, osversion, isa_level,
+			      soname);
 	}
 
       if (soname == NULL)
@@ -1096,6 +1102,7 @@ search_dir (const struct dir_entry *entry)
 		  dlib_ptr->name = xstrdup (direntry->d_name);
 		  dlib_ptr->is_link = is_link;
 		  dlib_ptr->osversion = osversion;
+		  dlib_ptr->isa_level = isa_level;
 		}
 	      /* Don't add this library, abort loop.  */
 	      /* Also free soname, since it's dynamically allocated.  */
@@ -1112,6 +1119,7 @@ search_dir (const struct dir_entry *entry)
 	  dlib_ptr->flag = flag;
 	  dlib_ptr->is_link = is_link;
 	  dlib_ptr->osversion = osversion;
+	  dlib_ptr->isa_level = isa_level;
 	  /* Add at head of list.  */
 	  dlib_ptr->next = dlibs;
 	  dlibs = dlib_ptr;
@@ -1149,7 +1157,7 @@ search_dir (const struct dir_entry *entry)
       if (opt_build_cache)
 	add_to_cache (entry->path, filename, dlib_ptr->soname,
 		      dlib_ptr->flag, dlib_ptr->osversion,
-		      hwcap, entry->hwcaps);
+		      dlib_ptr->isa_level, hwcap, entry->hwcaps);
     }
 
   /* Free all resources.  */

elf/readelflib.c

@@ -17,6 +17,8 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+#include <elf-read-prop.h>
+
 /* This code is a heavily simplified version of the readelf program
    that's part of the current binutils development version.  For architectures
    which need to handle both 32bit and 64bit ELF libraries,  this file is
@@ -40,8 +42,8 @@ do								\
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
+		  unsigned int *osversion, unsigned int *isa_level,
-		  size_t file_length)
+		  char **soname, void *file_contents, size_t file_length)
 {
   int i;
   unsigned int j;
@@ -86,6 +88,9 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
      libc5/libc6.  */
   *flag = FLAG_ELF;
 
+  /* The default ISA level is 0.  */
+  *isa_level = 0;
+
   dynamic_addr = 0;
   dynamic_size = 0;
   program_interpreter = NULL;
@@ -164,6 +169,78 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
 	    }
 	  break;
 
+	case PT_GNU_PROPERTY:
+	  /* The NT_GNU_PROPERTY_TYPE_0 note must be aligned to 4 bytes
+	     in 32-bit objects and to 8 bytes in 64-bit objects.  Skip
+	     notes with incorrect alignment.  */
+	  if (segment->p_align == (__ELF_NATIVE_CLASS / 8))
+	    {
+	      const ElfW(Nhdr) *note = (const void *) (file_contents
+						       + segment->p_offset);
+	      const ElfW(Addr) size = segment->p_filesz;
+	      const ElfW(Addr) align = segment->p_align;
+
+	      const ElfW(Addr) start = (ElfW(Addr)) (uintptr_t) note;
+	      unsigned int last_type = 0;
+
+	      while ((ElfW(Addr)) (uintptr_t) (note + 1) - start < size)
+		{
+		  /* Find the NT_GNU_PROPERTY_TYPE_0 note.  */
+		  if (note->n_namesz == 4
+		      && note->n_type == NT_GNU_PROPERTY_TYPE_0
+		      && memcmp (note + 1, "GNU", 4) == 0)
+		    {
+		      /* Check for invalid property.  */
+		      if (note->n_descsz < 8
+			  || (note->n_descsz % sizeof (ElfW(Addr))) != 0)
+			goto done;
+
+		      /* Start and end of property array.  */
+		      unsigned char *ptr = (unsigned char *) (note + 1) + 4;
+		      unsigned char *ptr_end = ptr + note->n_descsz;
+
+		      do
+			{
+			  unsigned int type = *(unsigned int *) ptr;
+			  unsigned int datasz = *(unsigned int *) (ptr + 4);
+
+			  /* Property type must be in ascending order.  */
+			  if (type < last_type)
+			    goto done;
+
+			  ptr += 8;
+			  if ((ptr + datasz) > ptr_end)
+			    goto done;
+
+			  last_type = type;
+
+			  /* Target specific property processing.
+			     Return value:
+			       false: Continue processing the properties.
+			       true : Stop processing the properties.
+			   */
+			  if (read_gnu_property (isa_level, type,
+						 datasz, ptr))
+			    goto done;
+
+			  /* Check the next property item.  */
+			  ptr += ALIGN_UP (datasz, sizeof (ElfW(Addr)));
+			}
+		      while ((ptr_end - ptr) >= 8);
+
+		      /* Only handle one NT_GNU_PROPERTY_TYPE_0.  */
+		      goto done;
+		    }
+
+		  note = ((const void *) note
+			  + ELF_NOTE_NEXT_OFFSET (note->n_namesz,
+						  note->n_descsz,
+						  align));
+		}
+	    }
+done:
+	  break;
+
 	default:
 	  break;
 	}

elf/readlib.c

@@ -75,7 +75,8 @@ is_gdb_python_file (const char *name)
 int
 process_file (const char *real_file_name, const char *file_name,
 	      const char *lib, int *flag, unsigned int *osversion,
-	      char **soname, int is_link, struct stat64 *stat_buf)
+	      unsigned int *isa_level, char **soname, int is_link,
+	      struct stat64 *stat_buf)
 {
   FILE *file;
   struct stat64 statbuf;
@@ -173,8 +174,8 @@ process_file (const char *real_file_name, const char *file_name,
   /* Libraries have to be shared object files.  */
   else if (elf_header->e_type != ET_DYN)
     ret = 1;
-  else if (process_elf_file (file_name, lib, flag, osversion, soname,
+  else if (process_elf_file (file_name, lib, flag, osversion, isa_level,
-			     file_contents, statbuf.st_size))
+			     soname, file_contents, statbuf.st_size))
     ret = 1;
 
  done:

elf/tst-glibc-hwcaps-2-cache.c

@@ -0,0 +1,45 @@
+/* Wrapper to invoke tst-glibc-hwcaps-2 in a container to test ldconfig.
+   Copyright (C) 2021 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
+   <https://www.gnu.org/licenses/>.  */
+
+/* This program is just a wrapper that runs ldconfig followed by
+   tst-glibc-hwcaps-2.  The actual test is provided via an
+   implementation in a sysdeps subdirectory.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <support/support.h>
+#include <support/capture_subprocess.h>
+
+int
+main (int argc, char **argv)
+{
+  /* Run ldconfig to populate the cache.  */
+  char *command = xasprintf ("%s/ldconfig", support_install_rootsbindir);
+  struct support_capture_subprocess result =
+    support_capture_subprogram (command,  &((char *) { NULL }));
+  support_capture_subprocess_check (&result, "ldconfig", 0, sc_allow_none);
+  free (command);
+
+  /* Reuse tst-glibc-hwcaps.  Since this code is running in a
+     container, we can launch it directly.  */
+  char *path = xasprintf ("%s/elf/tst-glibc-hwcaps-2", support_objdir_root);
+  execv (path, argv);
+  printf ("error: execv of %s failed: %m\n", path);
+  return 1;
+}

elf/tst-glibc-hwcaps-2-cache.root/etc/ld.so.conf

@@ -0,0 +1,2 @@
+# This file was created to suppress a warning from ldconfig:
+# /sbin/ldconfig: Warning: ignoring configuration file that cannot be opened: /etc/ld.so.conf: No such file or directory

elf/tst-glibc-hwcaps-2-cache.script

@@ -0,0 +1,8 @@
+# test-container does not support scripts in sysdeps directories, so
+# collect everything in one file.
+
+mkdirp 0770 $L/glibc-hwcaps/x86-64-v2
+mkdirp 0770 $L/glibc-hwcaps/x86-64-v3
+cp $B/elf/libx86-64-isa-level-1.so $L/libx86-64-isa-level.so
+cp $B/elf/libx86-64-isa-level-3.so $L/glibc-hwcaps/x86-64-v2/libx86-64-isa-level.so
+cp $B/elf/libx86-64-isa-level-4.so $L/glibc-hwcaps/x86-64-v3/libx86-64-isa-level.so

sysdeps/generic/dl-cache.h

@@ -106,14 +106,24 @@ struct file_entry_new
    entries.  */
 #define DL_CACHE_HWCAP_EXTENSION (1ULL << 62)
 
+/* The number of the ISA level bits in the upper 32 bits of the hwcap
+   field.  */
+#define DL_CACHE_HWCAP_ISA_LEVEL_COUNT 10
+
+/* The mask of the ISA level bits in the hwcap field.  */
+#define DL_CACHE_HWCAP_ISA_LEVEL_MASK \
+  ((1 << DL_CACHE_HWCAP_ISA_LEVEL_COUNT) -1)
+
 /* Return true if the ENTRY->hwcap value indicates that
    DL_CACHE_HWCAP_EXTENSION is used.  */
 static inline bool
 dl_cache_hwcap_extension (struct file_entry_new *entry)
 {
-  /* If DL_CACHE_HWCAP_EXTENSION is set, but other bits as well, this
+  /* This is an hwcap extension if only the DL_CACHE_HWCAP_EXTENSION bit
-     is a different kind of extension.  */
+     is set, ignoring the lower 32 bits as well as the ISA level bits in
-  return (entry->hwcap >> 32) == (DL_CACHE_HWCAP_EXTENSION >> 32);
+     the upper 32 bits.  */
+  return (((entry->hwcap >> 32) & ~DL_CACHE_HWCAP_ISA_LEVEL_MASK)
+	  == (DL_CACHE_HWCAP_EXTENSION >> 32));
 }
 
 /* See flags member of struct cache_file_new below.  */

sysdeps/generic/dl-isa-level.h

@@ -0,0 +1,25 @@
+/* Support for reading ISA level in /etc/ld.so.cache files written by
+   Linux ldconfig.  Generic version.
+   Copyright (C) 2021 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
+   <https://www.gnu.org/licenses/>.  */
+
+/* Return true if the ISA level in ENTRY is compatible with CPU.  */
+static inline bool
+dl_cache_hwcap_isa_level_compatible (struct file_entry_new *entry)
+{
+  return true;
+}

sysdeps/generic/elf-read-prop.h

@@ -0,0 +1,34 @@
+/* Support for GNU properties in ldconfig.  Generic version.
+   Copyright (C) 2021 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
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _ELF_READ_PROP_H
+#define _ELF_READ_PROP_H
+
+/* Called for each property in the NT_GNU_PROPERTY_TYPE_0 note of SEGMENT.
+   Return value:
+     false: Continue processing the properties.
+     true : Stop processing the properties.
+ */
+static inline bool __attribute__ ((always_inline))
+read_gnu_property (unsigned int *isal_level, uint32_t type, uint32_t
+		   datasz, void *data)
+{
+  return true;
+}
+
+#endif

sysdeps/generic/ldconfig.h

@@ -70,8 +70,9 @@ const char *glibc_hwcaps_subdirectory_name
   (const struct glibc_hwcaps_subdirectory *);
 
 extern void add_to_cache (const char *path, const char *filename,
-			  const char *soname,
+			  const char *soname, int flags,
-			  int flags, unsigned int osversion, uint64_t hwcap,
+			  unsigned int osversion, unsigned int isa_level,
+			  uint64_t hwcap,
 			  struct glibc_hwcaps_subdirectory *);
 
 extern void init_aux_cache (void);
@@ -79,23 +80,28 @@ extern void init_aux_cache (void);
 extern void load_aux_cache (const char *aux_cache_name);
 
 extern int search_aux_cache (struct stat64 *stat_buf, int *flags,
-			     unsigned int *osversion, char **soname);
+			     unsigned int *osversion,
+			     unsigned int *isa_level, char **soname);
 
 extern void add_to_aux_cache (struct stat64 *stat_buf, int flags,
-			      unsigned int osversion, const char *soname);
+			      unsigned int osversion,
+			      unsigned int isa_level, const char *soname);
 
 extern void save_aux_cache (const char *aux_cache_name);
 
 /* Declared in readlib.c.  */
 extern int process_file (const char *real_file_name, const char *file_name,
-			 const char *lib, int *flag, unsigned int *osversion,
+			 const char *lib, int *flag,
-			 char **soname, int is_link, struct stat64 *stat_buf);
+			 unsigned int *osversion, unsigned int *isa_level,
+			 char **soname, int is_link,
+			 struct stat64 *stat_buf);
 
 extern char *implicit_soname (const char *lib, int flag);
 
 /* Declared in readelflib.c.  */
-extern int process_elf_file (const char *file_name, const char *lib, int *flag,
+extern int process_elf_file (const char *file_name, const char *lib,
-			     unsigned int *osversion, char **soname,
+			     int *flag, unsigned int *osversion,
+			     unsigned int *isa_level, char **soname,
 			     void *file_contents, size_t file_length);
 
 /* Declared in chroot_canon.c.  */

sysdeps/unix/sysv/linux/arm/readelflib.c

@@ -18,18 +18,20 @@
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
+int process_elf32_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
+int process_elf64_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
+		  unsigned int *osversion, unsigned int *isa_level,
-		  size_t file_length)
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret;
@@ -38,8 +40,8 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
     {
       Elf32_Ehdr *elf32_header = (Elf32_Ehdr *) elf_header;
 
-      ret = process_elf32_file (file_name, lib, flag, osversion, soname,
+      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
-				file_contents, file_length);
+				soname, file_contents, file_length);
 
       if (!ret && EF_ARM_EABI_VERSION (elf32_header->e_flags) == EF_ARM_EABI_VER5)
 	{
@@ -57,8 +59,8 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
     }
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
-				file_contents, file_length);
+				soname, file_contents, file_length);
       /* AArch64 libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_AARCH64_LIB64|FLAG_ELF_LIBC6;

sysdeps/unix/sysv/linux/ia64/readelflib.c

@@ -16,29 +16,31 @@
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
+int process_elf32_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
+int process_elf64_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname,
+		  unsigned int *osversion, unsigned int *isa_level,
-		  void *file_contents, size_t file_length)
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret;
 
   if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
-    return process_elf32_file (file_name, lib, flag, osversion, soname,
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
-			       file_contents, file_length);
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
-				file_contents, file_length);
+				soname, file_contents, file_length);
       /* Intel 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_IA64_LIB64|FLAG_ELF_LIBC6;

sysdeps/unix/sysv/linux/mips/readelflib.c

@@ -20,18 +20,20 @@
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
+int process_elf32_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
+int process_elf64_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
+		  unsigned int *osversion, unsigned int *isa_level,
-		  size_t file_length)
+		  char **soname, void *file_contents, size_t file_length)
 {
   union
     {
@@ -45,8 +47,8 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
   elf_header.eh = file_contents;
   if (elf_header.eh->e_ident [EI_CLASS] == ELFCLASS32)
     {
-      ret = process_elf32_file (file_name, lib, flag, osversion, soname,
+      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
-				file_contents, file_length);
+				soname, file_contents, file_length);
       if (!ret)
 	{
 	  Elf32_Word flags = elf_header.eh32->e_flags;
@@ -62,8 +64,8 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
     }
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
-				file_contents, file_length);
+				soname, file_contents, file_length);
       /* n64 libraries are always libc.so.6+.  */
       if (!ret)
 	{

sysdeps/unix/sysv/linux/powerpc/readelflib.c

@@ -17,29 +17,31 @@
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
+int process_elf32_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
+int process_elf64_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
+		  unsigned int *osversion, unsigned int *isa_level,
-		  size_t file_length)
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret;
 
   if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
-    return process_elf32_file (file_name, lib, flag, osversion, soname,
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
-			       file_contents, file_length);
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
-				file_contents, file_length);
+				soname, file_contents, file_length);
       /* PowerPC 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_POWERPC_LIB64|FLAG_ELF_LIBC6;

sysdeps/unix/sysv/linux/riscv/readelflib.c

@@ -17,11 +17,13 @@
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
+int process_elf32_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
+int process_elf64_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* The ELF flags supported by our current glibc port:
@@ -38,8 +40,8 @@ int process_elf64_file (const char *file_name, const char *lib, int *flag,
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
+		  unsigned int *osversion, unsigned int *isa_level,
-		  size_t file_length)
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   Elf32_Ehdr *elf32_header = (Elf32_Ehdr *) elf_header;
@@ -52,14 +54,14 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
 
   if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
     {
-      ret = process_elf32_file (file_name, lib, flag, osversion, soname,
+      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
-				file_contents, file_length);
+				soname, file_contents, file_length);
       flags = elf32_header->e_flags;
     }
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
-				file_contents, file_length);
+				soname, file_contents, file_length);
       flags = elf64_header->e_flags;
     }
 

sysdeps/unix/sysv/linux/s390/readelflib.c

@@ -16,29 +16,31 @@
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
+int process_elf32_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
+int process_elf64_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
+		  unsigned int *osversion, unsigned int *isa_level,
-		  size_t file_length)
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret;
 
   if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
-    return process_elf32_file (file_name, lib, flag, osversion, soname,
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
-			       file_contents, file_length);
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
-				file_contents, file_length);
+				soname, file_contents, file_length);
       /* S/390 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_S390_LIB64|FLAG_ELF_LIBC6;

sysdeps/unix/sysv/linux/sparc/readelflib.c

@@ -18,29 +18,31 @@
    <https://www.gnu.org/licenses/>.  */
 
 
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
+int process_elf32_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
+int process_elf64_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
+		  unsigned int *osversion, unsigned int *isa_level,
-		  size_t file_length)
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret;
 
   if (elf_header->e_ident [EI_CLASS] == ELFCLASS32)
-    return process_elf32_file (file_name, lib, flag, osversion, soname,
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
-			       file_contents, file_length);
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
-				file_contents, file_length);
+				soname, file_contents, file_length);
       /* Sparc 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_SPARC_LIB64|FLAG_ELF_LIBC6;

sysdeps/unix/sysv/linux/x86/elf-read-prop.h

@@ -0,0 +1,60 @@
+/* Support for GNU properties in ldconfig.  x86 version.
+   Copyright (C) 2021 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
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _ELF_READ_PROP_H
+#define _ELF_READ_PROP_H
+
+#include <dl-cache.h>
+
+/* Called for each property in the NT_GNU_PROPERTY_TYPE_0 note of SEGMENT.
+   Return value:
+     false: Continue processing the properties.
+     true : Stop processing the properties.
+ */
+static inline bool __attribute__ ((always_inline))
+read_gnu_property (unsigned int *isal_level, uint32_t type,
+		   uint32_t datasz, void *data)
+{
+  /* Property type must be in ascending order.  */
+  if (type > GNU_PROPERTY_X86_ISA_1_NEEDED)
+    return true;
+
+  if (type == GNU_PROPERTY_X86_ISA_1_NEEDED)
+    {
+      if (datasz == 4)
+	{
+	  /* The size of GNU_PROPERTY_X86_ISA_1_NEEDED must be 4 bytes.
+	     There is no point to continue if this type is ill-formed.  */
+	  unsigned int isa_1_needed = *(unsigned int *) data;
+	  _Static_assert (((sizeof (isa_1_needed) * 8)
+			   <= (1 << DL_CACHE_HWCAP_ISA_LEVEL_COUNT)),
+			  "DL_CACHE_HWCAP_ISA_LEVEL_COUNT is too small");
+	  if (isa_1_needed != 0)
+	    {
+	      unsigned int level;
+	      asm ("bsr %1, %0" : "=r" (level) : "g" (isa_1_needed));
+	      *isal_level = level;
+	    }
+	}
+      return true;
+    }
+
+  return false;
+}
+
+#endif

sysdeps/unix/sysv/linux/x86/readelflib.c

@@ -17,19 +17,20 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-
+int process_elf32_file (const char *file_name, const char *lib,
-int process_elf32_file (const char *file_name, const char *lib, int *flag,
+			int *flag, unsigned int *osversion,
-			unsigned int *osversion, char **soname,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
-int process_elf64_file (const char *file_name, const char *lib, int *flag,
+int process_elf64_file (const char *file_name, const char *lib,
-			unsigned int *osversion, char **soname,
+			int *flag, unsigned int *osversion,
+			unsigned int *isa_level, char **soname,
 			void *file_contents, size_t file_length);
 
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
-		  unsigned int *osversion, char **soname, void *file_contents,
+		  unsigned int *osversion, unsigned int *isa_level,
-		  size_t file_length)
+		  char **soname, void *file_contents, size_t file_length)
 {
   ElfW(Ehdr) *elf_header = (ElfW(Ehdr) *) file_contents;
   int ret, file_flag = 0;
@@ -68,11 +69,11 @@ failed:
     }
 
   if (elf_header->e_ident[EI_CLASS] == ELFCLASS32)
-    ret = process_elf32_file (file_name, lib, flag, osversion, soname,
+    ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
-			      file_contents, file_length);
+			      soname, file_contents, file_length);
   else
-    ret = process_elf64_file (file_name, lib, flag, osversion, soname,
+    ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
-			      file_contents, file_length);
+			      soname, file_contents, file_length);
 
   if (!ret && file_flag)
     *flag = file_flag;

sysdeps/unix/sysv/linux/x86_64/Makefile

@@ -13,3 +13,54 @@ endif
 ifeq ($(subdir),misc)
 gen-as-const-headers += sigaltstack-offsets.sym
 endif
+
+ifeq ($(subdir),elf)
+ifeq (yes,$(enable-x86-isa-level))
+tests += \
+  tst-glibc-hwcaps-2
+ifeq (no,$(build-hardcoded-path-in-tests))
+# This is an ld.so.cache test, and RPATH/RUNPATH in the executable
+# interferes with its test objectives.
+tests-container += \
+  tst-glibc-hwcaps-2-cache
+endif
+modules-names += \
+  libx86-64-isa-level-1 \
+  libx86-64-isa-level-2 \
+  libx86-64-isa-level-3 \
+  libx86-64-isa-level-4
+
+$(objpfx)tst-glibc-hwcaps-2: $(objpfx)libx86-64-isa-level.so
+
+$(objpfx)tst-glibc-hwcaps-2.out: \
+  $(objpfx)glibc-hwcaps/x86-64-v2/libx86-64-isa-level.so \
+  $(objpfx)glibc-hwcaps/x86-64-v4/libx86-64-isa-level.so \
+  $(objpfx)glibc-hwcaps/x86-64-v3/libx86-64-isa-level.so
+$(objpfx)glibc-hwcaps/x86-64-v2/libx86-64-isa-level.so: \
+  $(objpfx)libx86-64-isa-level-2.so
+	$(make-target-directory)
+	cp $< $@
+$(objpfx)glibc-hwcaps/x86-64-v3/libx86-64-isa-level.so: \
+  $(objpfx)libx86-64-isa-level-3.so
+	$(make-target-directory)
+	cp $< $@
+$(objpfx)glibc-hwcaps/x86-64-v4/libx86-64-isa-level.so: \
+  $(objpfx)libx86-64-isa-level-4.so
+	$(make-target-directory)
+	cp $< $@
+
+CFLAGS-libx86-64-isa-level-1.os += -march=x86-64
+CFLAGS-libx86-64-isa-level-2.os += -march=x86-64
+CFLAGS-libx86-64-isa-level-3.os += -march=x86-64
+CFLAGS-libx86-64-isa-level-4.os += -march=x86-64
+
+# The test modules are parameterized by preprocessor macros.
+LDFLAGS-libx86-64-isa-level-1.so += -Wl,-soname,libx86-64-isa-level.so
+LDFLAGS-libx86-64-isa-level-4.so += -Wl,-soname,libx86-64-isa-level.so
+$(objpfx)libx86-64-isa-level%.os: $(..)/sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c
+	$(compile-command.c) -DVALUE=$(lastword $(subst -, ,$*)) \
+	  -DISA_LEVEL="(1 << ($(lastword $(subst -, ,$*)) - 1))"
+$(objpfx)libx86-64-isa-level.so: $(objpfx)libx86-64-isa-level-1.so
+	cp $< $@
+endif
+endif # $(subdir) == elf

sysdeps/unix/sysv/linux/x86_64/tst-glibc-hwcaps-2.c

@@ -0,0 +1,84 @@
+/* Check ISA level on shared object in glibc-hwcaps subdirectories.
+   Copyright (C) 2021 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <elf.h>
+#include <get-isa-level.h>
+#include <support/check.h>
+#include <support/test-driver.h>
+
+extern int dso_isa_level (void);
+
+static int
+do_test (void)
+{
+  const struct cpu_features *cpu_features
+    = __x86_get_cpu_features (COMMON_CPUID_INDEX_MAX);
+  unsigned int isa_level = get_isa_level (cpu_features);
+  bool has_isa_baseline = ((isa_level & GNU_PROPERTY_X86_ISA_1_BASELINE)
+			   == GNU_PROPERTY_X86_ISA_1_BASELINE);
+  bool has_isa_v2 = ((isa_level & GNU_PROPERTY_X86_ISA_1_V2)
+			   == GNU_PROPERTY_X86_ISA_1_V2);
+  bool has_isa_v3 = ((isa_level & GNU_PROPERTY_X86_ISA_1_V3)
+			   == GNU_PROPERTY_X86_ISA_1_V3);
+  bool has_isa_v4 = ((isa_level & GNU_PROPERTY_X86_ISA_1_V4)
+			   == GNU_PROPERTY_X86_ISA_1_V4);
+
+  if (!has_isa_baseline)
+    return EXIT_FAILURE;
+
+  int level = dso_isa_level ();
+  int ret;
+  switch (level)
+    {
+    case 1:
+    case 2:
+      /* The default libx86-64-isa-level.so is used.  */
+      printf ("The default shared library is used.\n");
+      if (has_isa_v3 || has_isa_v4 || !has_isa_v2)
+	ret = EXIT_FAILURE;
+      else
+	ret = EXIT_SUCCESS;
+      break;
+    case 3:
+      /* libx86-64-isa-level.so marked as x86-64 ISA level 3 needed in
+	 x86-64-v2 should be ignored on lesser CPU.  */
+      printf ("x86-64 ISA level 3 shared library is used.\n");
+      if (has_isa_v4 || !has_isa_v3)
+	ret = EXIT_FAILURE;
+      else
+	ret = EXIT_SUCCESS;
+      break;
+    case 4:
+      /* libx86-64-isa-level.so marked as x86-64 ISA level 4 needed in
+	 x86-64-v3 should be ignored on lesser CPU.  */
+      printf ("x86-64 ISA level 4 shared library is used.\n");
+      if (has_isa_v4)
+	ret = EXIT_SUCCESS;
+      else
+	ret = EXIT_FAILURE;
+      break;
+    default:
+      abort ();
+    }
+  return ret;
+}
+
+#include <support/test-driver.c>

sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c

@@ -0,0 +1,4 @@
+#define INCLUDE_X86_ISA_LEVEL
+#define MARKER dso_isa_level
+#include <isa-level.c>
+#include <markermodMARKER-VALUE.c>

sysdeps/x86/dl-isa-level.h

@@ -0,0 +1,31 @@
+/* Support for reading ISA level in /etc/ld.so.cache files written by
+   Linux ldconfig.  x86 version.
+   Copyright (C) 2021 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sys/platform/x86.h>
+
+/* Return true if the ISA level in ENTRY is compatible with CPU.  */
+static inline bool
+dl_cache_hwcap_isa_level_compatible (struct file_entry_new *entry)
+{
+  const struct cpu_features *cpu_features = __get_cpu_features ();
+  unsigned int isa_level
+    = 1 << ((entry->hwcap >> 32) & DL_CACHE_HWCAP_ISA_LEVEL_MASK);
+
+  return (isa_level & cpu_features->isa_1) == isa_level;
+}