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.

17 files changed, 412 insertions, 92 deletions

diff --git a/sysdeps/generic/dl-cache.h b/sysdeps/generic/dl-cache.h
index c7eca70d0c..964d50a486 100644
--- a/sysdeps/generic/dl-cache.h
+++ b/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
-     is a different kind of extension.  */
-  return (entry->hwcap >> 32) == (DL_CACHE_HWCAP_EXTENSION >> 32);
+  /* This is an hwcap extension if only the DL_CACHE_HWCAP_EXTENSION bit
+     is set, ignoring the lower 32 bits as well as the ISA level bits in
+     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.  */
diff --git a/sysdeps/generic/dl-isa-level.h b/sysdeps/generic/dl-isa-level.h
new file mode 100644
index 0000000000..6fcd319c49
--- /dev/null
+++ b/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;
+}
diff --git a/sysdeps/generic/elf-read-prop.h b/sysdeps/generic/elf-read-prop.h
new file mode 100644
index 0000000000..98c3d2acb5
--- /dev/null
+++ b/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
diff --git a/sysdeps/generic/ldconfig.h b/sysdeps/generic/ldconfig.h
index eb070fd259..3ab757077d 100644
--- a/sysdeps/generic/ldconfig.h
+++ b/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,
-			  int flags, unsigned int osversion, uint64_t hwcap,
+			  const char *soname, int flags,
+			  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,
-			 char **soname, int is_link, struct stat64 *stat_buf);
+			 const char *lib, int *flag,
+			 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,
-			     unsigned int *osversion, char **soname,
+extern int process_elf_file (const char *file_name, const char *lib,
+			     int *flag, unsigned int *osversion,
+			     unsigned int *isa_level, char **soname,
 			     void *file_contents, size_t file_length);
 
 /* Declared in chroot_canon.c.  */
diff --git a/sysdeps/unix/sysv/linux/arm/readelflib.c b/sysdeps/unix/sysv/linux/arm/readelflib.c
index 2d3ecb1eef..ade2f49aeb 100644
--- a/sysdeps/unix/sysv/linux/arm/readelflib.c
+++ b/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,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			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,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			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,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  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,
-				file_contents, file_length);
+      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
+				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,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* AArch64 libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_AARCH64_LIB64|FLAG_ELF_LIBC6;
diff --git a/sysdeps/unix/sysv/linux/ia64/readelflib.c b/sysdeps/unix/sysv/linux/ia64/readelflib.c
index 7fb3ace359..2aa32666aa 100644
--- a/sysdeps/unix/sysv/linux/ia64/readelflib.c
+++ b/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,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			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,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			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, size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  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,
-			       file_contents, file_length);
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* Intel 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_IA64_LIB64|FLAG_ELF_LIBC6;
diff --git a/sysdeps/unix/sysv/linux/mips/readelflib.c b/sysdeps/unix/sysv/linux/mips/readelflib.c
index e50bc3ce23..d0e809d893 100644
--- a/sysdeps/unix/sysv/linux/mips/readelflib.c
+++ b/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,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			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,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			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,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  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,
-				file_contents, file_length);
+      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
+				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,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* n64 libraries are always libc.so.6+.  */
       if (!ret)
 	{
diff --git a/sysdeps/unix/sysv/linux/powerpc/readelflib.c b/sysdeps/unix/sysv/linux/powerpc/readelflib.c
index 4f9a9be254..51f8a9496a 100644
--- a/sysdeps/unix/sysv/linux/powerpc/readelflib.c
+++ b/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,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			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,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			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,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  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,
-			       file_contents, file_length);
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* PowerPC 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_POWERPC_LIB64|FLAG_ELF_LIBC6;
diff --git a/sysdeps/unix/sysv/linux/riscv/readelflib.c b/sysdeps/unix/sysv/linux/riscv/readelflib.c
index 2aca6670a8..3822d63a05 100644
--- a/sysdeps/unix/sysv/linux/riscv/readelflib.c
+++ b/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,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			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,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			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,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  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,
-				file_contents, file_length);
+      ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       flags = elf32_header->e_flags;
     }
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       flags = elf64_header->e_flags;
     }
 
diff --git a/sysdeps/unix/sysv/linux/s390/readelflib.c b/sysdeps/unix/sysv/linux/s390/readelflib.c
index fc21af34d8..e190109e3d 100644
--- a/sysdeps/unix/sysv/linux/s390/readelflib.c
+++ b/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,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			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,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			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,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  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,
-			       file_contents, file_length);
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* S/390 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_S390_LIB64|FLAG_ELF_LIBC6;
diff --git a/sysdeps/unix/sysv/linux/sparc/readelflib.c b/sysdeps/unix/sysv/linux/sparc/readelflib.c
index d54b8dfd28..bbfc81337a 100644
--- a/sysdeps/unix/sysv/linux/sparc/readelflib.c
+++ b/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,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			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,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			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,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  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,
-			       file_contents, file_length);
+    return process_elf32_file (file_name, lib, flag, osversion, isa_level,
+			       soname, file_contents, file_length);
   else
     {
-      ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-				file_contents, file_length);
+      ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+				soname, file_contents, file_length);
       /* Sparc 64bit libraries are always libc.so.6+.  */
       if (!ret)
 	*flag = FLAG_SPARC_LIB64|FLAG_ELF_LIBC6;
diff --git a/sysdeps/unix/sysv/linux/x86/elf-read-prop.h b/sysdeps/unix/sysv/linux/x86/elf-read-prop.h
new file mode 100644
index 0000000000..85affa2864
--- /dev/null
+++ b/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
diff --git a/sysdeps/unix/sysv/linux/x86/readelflib.c b/sysdeps/unix/sysv/linux/x86/readelflib.c
index a4df70e7e6..4a9bcc82cb 100644
--- a/sysdeps/unix/sysv/linux/x86/readelflib.c
+++ b/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 *flag,
-			unsigned int *osversion, char **soname,
+int process_elf32_file (const char *file_name, const char *lib,
+			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,
-			unsigned int *osversion, char **soname,
+int process_elf64_file (const char *file_name, const char *lib,
+			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,
-		  size_t file_length)
+		  unsigned int *osversion, unsigned int *isa_level,
+		  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,
-			      file_contents, file_length);
+    ret = process_elf32_file (file_name, lib, flag, osversion, isa_level,
+			      soname, file_contents, file_length);
   else
-    ret = process_elf64_file (file_name, lib, flag, osversion, soname,
-			      file_contents, file_length);
+    ret = process_elf64_file (file_name, lib, flag, osversion, isa_level,
+			      soname, file_contents, file_length);
 
   if (!ret && file_flag)
     *flag = file_flag;
diff --git a/sysdeps/unix/sysv/linux/x86_64/Makefile b/sysdeps/unix/sysv/linux/x86_64/Makefile
index 9b82155393..5e19202ebf 100644
--- a/sysdeps/unix/sysv/linux/x86_64/Makefile
+++ b/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
diff --git a/sysdeps/unix/sysv/linux/x86_64/tst-glibc-hwcaps-2.c b/sysdeps/unix/sysv/linux/x86_64/tst-glibc-hwcaps-2.c
new file mode 100644
index 0000000000..fe91bfd224
--- /dev/null
+++ b/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>
diff --git a/sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c b/sysdeps/unix/sysv/linux/x86_64/x86-64-isa-level-VALUE.c
new file mode 100644
index 0000000000..2813d627cc
--- /dev/null
+++ b/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>
diff --git a/sysdeps/x86/dl-isa-level.h b/sysdeps/x86/dl-isa-level.h
new file mode 100644
index 0000000000..afe390c365
--- /dev/null
+++ b/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;
+}