commit dad90d528259b669342757c37dedefa8577e2636

Author: Florian Weimer <fweimer@redhat.com>

Date:   Fri Dec 4 09:13:43 2020 +0100

    elf: Add glibc-hwcaps support for LD_LIBRARY_PATH

    This hacks non-power-set processing into _dl_important_hwcaps.

    Once the legacy hwcaps handling goes away, the subdirectory

    handling needs to be reworked, but it is premature to do this

    while both approaches are still supported.

    ld.so supports two new arguments, --glibc-hwcaps-prepend and

    --glibc-hwcaps-mask.  Each accepts a colon-separated list of

    glibc-hwcaps subdirectory names.  The prepend option adds additional

    subdirectories that are searched first, in the specified order.  The

    mask option restricts the automatically selected subdirectories to

    those listed in the option argument.  For example, on systems where

    /usr/lib64 is on the library search path,

    --glibc-hwcaps-prepend=valgrind:debug causes the dynamic loader to

    search the directories /usr/lib64/glibc-hwcaps/valgrind and

    /usr/lib64/glibc-hwcaps/debug just before /usr/lib64 is searched.

    Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

Conflicts:

	elf/Makefile

	  (Test backport differences.)

diff --git a/elf/Makefile b/elf/Makefile

index bc96b8fd65e376cc..f795617780b393ec 100644

--- a/elf/Makefile

+++ b/elf/Makefile

@@ -59,7 +59,8 @@ elide-routines.os = $(all-dl-routines) dl-support enbl-secure dl-origin \

 # ld.so uses those routines, plus some special stuff for being the program

 # interpreter and operating independent of libc.

 rtld-routines	= rtld $(all-dl-routines) dl-sysdep dl-environ dl-minimal \

-  dl-error-minimal dl-conflict dl-hwcaps dl-usage

+  dl-error-minimal dl-conflict dl-hwcaps dl-hwcaps_split dl-hwcaps-subdirs \

+  dl-usage

 all-rtld-routines = $(rtld-routines) $(sysdep-rtld-routines)

 CFLAGS-dl-runtime.c += -fexceptions -fasynchronous-unwind-tables

@@ -199,13 +200,14 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \

 	 tst-filterobj tst-filterobj-dlopen tst-auxobj tst-auxobj-dlopen \

 	 tst-audit14 tst-audit15 tst-audit16 \

 	 tst-tls-ie tst-tls-ie-dlmopen \

-	 argv0test

+	 argv0test \

+	 tst-glibc-hwcaps tst-glibc-hwcaps-prepend tst-glibc-hwcaps-mask

 #	 reldep9

 tests-internal += loadtest unload unload2 circleload1 \

 	 neededtest neededtest2 neededtest3 neededtest4 \

 	 tst-tls3 tst-tls6 tst-tls7 tst-tls8 tst-dlmopen2 \

 	 tst-ptrguard1 tst-stackguard1 tst-libc_dlvsym \

-	 tst-create_format1 tst-tls-surplus

+	 tst-create_format1 tst-tls-surplus tst-dl-hwcaps_split

 tests-container += tst-pldd

 ifeq ($(build-hardcoded-path-in-tests),yes)

 tests += tst-dlopen-aout

@@ -318,7 +320,10 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \

 		tst-auditlogmod-1 tst-auditlogmod-2 tst-auditlogmod-3 \

 		tst-tls-ie-mod0 tst-tls-ie-mod1 tst-tls-ie-mod2 \

 		tst-tls-ie-mod3 tst-tls-ie-mod4 tst-tls-ie-mod5 \

-		tst-tls-ie-mod6

+		tst-tls-ie-mod6 libmarkermod1-1 libmarkermod1-2 libmarkermod1-3 \

+		libmarkermod2-1 libmarkermod2-2 \

+		libmarkermod3-1 libmarkermod3-2 libmarkermod3-3 \

+		libmarkermod4-1 libmarkermod4-2 libmarkermod4-3 libmarkermod4-4 \

 # Most modules build with _ISOMAC defined, but those filtered out

 # depend on internal headers.

@@ -1732,3 +1737,60 @@ $(objpfx)argv0test.out: tst-rtld-argv0.sh $(objpfx)ld.so \

             '$(test-wrapper-env)' '$(run_program_env)' \

             '$(rpath-link)' 'test-argv0' > $@; \

     $(evaluate-test)

+

+# A list containing the name of the most likely searched subdirectory

+# of the glibc-hwcaps directory, for each supported architecture (in

+# other words, the oldest hardware level recognized by the

+# glibc-hwcaps mechanism for this architecture).  Used to obtain test

+# coverage for some glibc-hwcaps tests for the widest possible range

+# of systems.

+glibc-hwcaps-first-subdirs-for-tests =

+

+# The test modules are parameterized by preprocessor macros.

+LDFLAGS-libmarkermod1-1.so += -Wl,-soname,libmarkermod1.so

+LDFLAGS-libmarkermod2-1.so += -Wl,-soname,libmarkermod2.so

+LDFLAGS-libmarkermod3-1.so += -Wl,-soname,libmarkermod3.so

+LDFLAGS-libmarkermod4-1.so += -Wl,-soname,libmarkermod4.so

+$(objpfx)libmarkermod%.os : markermodMARKER-VALUE.c

+	$(compile-command.c) \

+	  -DMARKER=marker$(firstword $(subst -, ,$*)) \

+	  -DVALUE=$(lastword $(subst -, ,$*))

+$(objpfx)libmarkermod1.so: $(objpfx)libmarkermod1-1.so

+	cp $< $@

+$(objpfx)libmarkermod2.so: $(objpfx)libmarkermod2-1.so

+	cp $< $@

+$(objpfx)libmarkermod3.so: $(objpfx)libmarkermod3-1.so

+	cp $< $@

+$(objpfx)libmarkermod4.so: $(objpfx)libmarkermod4-1.so

+	cp $< $@

+

+# tst-glibc-hwcaps-prepend checks that --glibc-hwcaps-prepend is

+# preferred over auto-detected subdirectories.

+$(objpfx)tst-glibc-hwcaps-prepend: $(objpfx)libmarkermod1-1.so

+$(objpfx)glibc-hwcaps/prepend-markermod1/libmarkermod1.so: \

+  $(objpfx)libmarkermod1-2.so

+	$(make-target-directory)

+	cp $< $@

+$(objpfx)glibc-hwcaps/%/libmarkermod1.so: $(objpfx)libmarkermod1-3.so

+	$(make-target-directory)

+	cp $< $@

+$(objpfx)tst-glibc-hwcaps-prepend.out: \

+  $(objpfx)tst-glibc-hwcaps-prepend $(objpfx)libmarkermod1.so \

+  $(patsubst %,$(objpfx)glibc-hwcaps/%/libmarkermod1.so,prepend-markermod1 \

+    $(glibc-hwcaps-first-subdirs-for-tests))

+	$(test-wrapper) $(rtld-prefix) \

+	  --glibc-hwcaps-prepend prepend-markermod1 \

+	  $< > $@; \

+	$(evaluate-test)

+

+# tst-glibc-hwcaps-mask checks that --glibc-hwcaps-mask can be used to

+# suppress all auto-detected subdirectories.

+$(objpfx)tst-glibc-hwcaps-mask: $(objpfx)libmarkermod1-1.so

+$(objpfx)tst-glibc-hwcaps-mask.out: \

+  $(objpfx)tst-glibc-hwcaps-mask $(objpfx)libmarkermod1.so \

+  $(patsubst %,$(objpfx)glibc-hwcaps/%/libmarkermod1.so,\

+    $(glibc-hwcaps-first-subdirs-for-tests))

+	$(test-wrapper) $(rtld-prefix) \

+	  --glibc-hwcaps-mask does-not-exist \

+	  $< > $@; \

+	$(evaluate-test)

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

new file mode 100644

index 0000000000000000..60c6d59731ee3188

--- /dev/null

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

@@ -0,0 +1,29 @@

+/* Architecture-specific glibc-hwcaps subdirectories.  Generic version.

+   Copyright (C) 2020 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 <dl-hwcaps.h>

+

+/* In the generic version, there are no subdirectories defined.  */

+

+const char _dl_hwcaps_subdirs[] = "";

+

+uint32_t

+_dl_hwcaps_subdirs_active (void)

+{

+  return 0;

+}

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

index 82ee89c36a1eb4ab..e57d0d2d41741021 100644

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

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

@@ -26,20 +26,97 @@

 #include <dl-procinfo.h>

 #include <dl-hwcaps.h>

+/* This is the result of counting the substrings in a colon-separated

+   hwcaps string.  */

+struct hwcaps_counts

+{

+  /* Number of substrings.  */

+  size_t count;

+

+  /* Sum of the individual substring lengths (without separators or

+     null terminators).  */

+  size_t total_length;

+

+  /* Maximum length of an individual substring.  */

+  size_t maximum_length;

+};

+

+/* Update *COUNTS according to the contents of HWCAPS.  Skip over

+   entries whose bit is not set in MASK.  */

+static void

+update_hwcaps_counts (struct hwcaps_counts *counts, const char *hwcaps,

+		      uint32_t bitmask, const char *mask)

+{

+  struct dl_hwcaps_split_masked sp;

+  _dl_hwcaps_split_masked_init (&sp, hwcaps, bitmask, mask);

+  while (_dl_hwcaps_split_masked (&sp))

+    {

+      ++counts->count;

+      counts->total_length += sp.split.length;

+      if (sp.split.length > counts->maximum_length)

+	counts->maximum_length = sp.split.length;

+    }

+}

+

+/* State for copy_hwcaps.  Must be initialized to point to

+   the storage areas for the array and the strings themselves.  */

+struct copy_hwcaps

+{

+  struct r_strlenpair *next_pair;

+  char *next_string;

+};

+

+/* Copy HWCAPS into the string pairs and strings, advancing *TARGET.

+   Skip over entries whose bit is not set in MASK.  */

+static void

+copy_hwcaps (struct copy_hwcaps *target, const char *hwcaps,

+	     uint32_t bitmask, const char *mask)

+{

+  struct dl_hwcaps_split_masked sp;

+  _dl_hwcaps_split_masked_init (&sp, hwcaps, bitmask, mask);

+  while (_dl_hwcaps_split_masked (&sp))

+    {

+      target->next_pair->str = target->next_string;

+      char *slash = __mempcpy (__mempcpy (target->next_string,

+					  GLIBC_HWCAPS_PREFIX,

+					  strlen (GLIBC_HWCAPS_PREFIX)),

+			       sp.split.segment, sp.split.length);

+      *slash = '/';

+      target->next_pair->len

+	= strlen (GLIBC_HWCAPS_PREFIX) + sp.split.length + 1;

+      ++target->next_pair;

+      target->next_string = slash + 1;

+    }

+}

+

 /* Return an array of useful/necessary hardware capability names.  */

 const struct r_strlenpair *

-_dl_important_hwcaps (size_t *sz, size_t *max_capstrlen)

+_dl_important_hwcaps (const char *glibc_hwcaps_prepend,

+		      const char *glibc_hwcaps_mask,

+		      size_t *sz, size_t *max_capstrlen)

 {

   uint64_t hwcap_mask = GET_HWCAP_MASK();

   /* Determine how many important bits are set.  */

   uint64_t masked = GLRO(dl_hwcap) & hwcap_mask;

   size_t cnt = GLRO (dl_platform) != NULL;

   size_t n, m;

-  size_t total;

   struct r_strlenpair *result;

   struct r_strlenpair *rp;

   char *cp;

+  /* glibc-hwcaps subdirectories.  These are exempted from the power

+     set construction below.  */

+  uint32_t hwcaps_subdirs_active = _dl_hwcaps_subdirs_active ();

+  struct hwcaps_counts hwcaps_counts =  { 0, };

+  update_hwcaps_counts (&hwcaps_counts, glibc_hwcaps_prepend, -1, NULL);

+  update_hwcaps_counts (&hwcaps_counts, _dl_hwcaps_subdirs,

+			hwcaps_subdirs_active, glibc_hwcaps_mask);

+

+  /* Each hwcaps subdirectory has a GLIBC_HWCAPS_PREFIX string prefix

+     and a "/" suffix once stored in the result.  */

+  size_t total = (hwcaps_counts.count * (strlen (GLIBC_HWCAPS_PREFIX) + 1)

+		  + hwcaps_counts.total_length);

+

   /* Count the number of bits set in the masked value.  */

   for (n = 0; (~((1ULL << n) - 1) & masked) != 0; ++n)

     if ((masked & (1ULL << n)) != 0)

@@ -74,10 +151,10 @@ _dl_important_hwcaps (size_t *sz, size_t *max_capstrlen)

   /* Determine the total size of all strings together.  */

   if (cnt == 1)

-    total = temp[0].len + 1;

+    total += temp[0].len + 1;

   else

     {

-      total = temp[0].len + temp[cnt - 1].len + 2;

+      total += temp[0].len + temp[cnt - 1].len + 2;

       if (cnt > 2)

 	{

 	  total <<= 1;

@@ -94,26 +171,48 @@ _dl_important_hwcaps (size_t *sz, size_t *max_capstrlen)

 	}

     }

-  /* The result structure: we use a very compressed way to store the

-     various combinations of capability names.  */

-  *sz = 1 << cnt;

-  result = (struct r_strlenpair *) malloc (*sz * sizeof (*result) + total);

-  if (result == NULL)

+  *sz = hwcaps_counts.count + (1 << cnt);

+

+  /* This is the overall result, including both glibc-hwcaps

+     subdirectories and the legacy hwcaps subdirectories using the

+     power set construction.  */

+  struct r_strlenpair *overall_result

+    = malloc (*sz * sizeof (*result) + total);

+  if (overall_result == NULL)

     _dl_signal_error (ENOMEM, NULL, NULL,

 		      N_("cannot create capability list"));

+  /* Fill in the glibc-hwcaps subdirectories.  */

+  {

+    struct copy_hwcaps target;

+    target.next_pair = overall_result;

+    target.next_string = (char *) (overall_result + *sz);

+    copy_hwcaps (&target, glibc_hwcaps_prepend, -1, NULL);

+    copy_hwcaps (&target, _dl_hwcaps_subdirs,

+		 hwcaps_subdirs_active, glibc_hwcaps_mask);

+    /* Set up the write target for the power set construction.  */

+    result = target.next_pair;

+    cp = target.next_string;

+  }

+

+

+  /* Power set construction begins here.  We use a very compressed way

+     to store the various combinations of capability names.  */

+

   if (cnt == 1)

     {

-      result[0].str = (char *) (result + *sz);

+      result[0].str = cp;

       result[0].len = temp[0].len + 1;

-      result[1].str = (char *) (result + *sz);

+      result[1].str = cp;

       result[1].len = 0;

-      cp = __mempcpy ((char *) (result + *sz), temp[0].str, temp[0].len);

+      cp = __mempcpy (cp, temp[0].str, temp[0].len);

       *cp = '/';

-      *sz = 2;

-      *max_capstrlen = result[0].len;

+      if (result[0].len > hwcaps_counts.maximum_length)

+	*max_capstrlen = result[0].len;

+      else

+	*max_capstrlen = hwcaps_counts.maximum_length;

-      return result;

+      return overall_result;

     }

   /* Fill in the information.  This follows the following scheme

@@ -124,7 +223,7 @@ _dl_important_hwcaps (size_t *sz, size_t *max_capstrlen)

 	      #3: 0, 3			1001

      This allows the representation of all possible combinations of

      capability names in the string.  First generate the strings.  */

-  result[1].str = result[0].str = cp = (char *) (result + *sz);

+  result[1].str = result[0].str = cp;

 #define add(idx) \

       cp = __mempcpy (__mempcpy (cp, temp[idx].str, temp[idx].len), "/", 1);

   if (cnt == 2)

@@ -191,7 +290,10 @@ _dl_important_hwcaps (size_t *sz, size_t *max_capstrlen)

   while (--n != 0);

   /* The maximum string length.  */

-  *max_capstrlen = result[0].len;

+  if (result[0].len > hwcaps_counts.maximum_length)

+    *max_capstrlen = result[0].len;

+  else

+    *max_capstrlen = hwcaps_counts.maximum_length;

-  return result;

+  return overall_result;

 }

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

index d69ee11dc27bb5e5..3fcfbceb1a8fc1c8 100644

--- a/elf/dl-hwcaps.h

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

@@ -16,6 +16,11 @@

    License along with the GNU C Library; if not, see

    <http://www.gnu.org/licenses/>.  */

+#ifndef _DL_HWCAPS_H

+#define _DL_HWCAPS_H

+

+#include <stdint.h>

+

 #include <elf/dl-tunables.h>

 #if HAVE_TUNABLES

@@ -28,3 +33,103 @@

 #  define GET_HWCAP_MASK() (0)

 # endif

 #endif

+

+#define GLIBC_HWCAPS_SUBDIRECTORY "glibc-hwcaps"

+#define GLIBC_HWCAPS_PREFIX GLIBC_HWCAPS_SUBDIRECTORY "/"

+

+/* Used by _dl_hwcaps_split below, to split strings at ':'

+   separators.  */

+struct dl_hwcaps_split

+{

+  const char *segment;          /* Start of the current segment.  */

+  size_t length;                /* Number of bytes until ':' or NUL.  */

+};

+

+/* Prepare *S to parse SUBJECT, for future _dl_hwcaps_split calls.  If

+   SUBJECT is NULL, it is treated as the empty string.  */

+static inline void

+_dl_hwcaps_split_init (struct dl_hwcaps_split *s, const char *subject)

+{

+  s->segment = subject;

+  /* The initial call to _dl_hwcaps_split will not skip anything.  */

+  s->length = 0;

+}

+

+/* Extract the next non-empty string segment, up to ':' or the null

+   terminator.  Return true if one more segment was found, or false if

+   the end of the string was reached.  On success, S->segment is the

+   start of the segment found, and S->length is its length.

+   (Typically, S->segment[S->length] is not null.)  */

+_Bool _dl_hwcaps_split (struct dl_hwcaps_split *s) attribute_hidden;

+

+/* Similar to dl_hwcaps_split, but with bit-based and name-based

+   masking.  */

+struct dl_hwcaps_split_masked

+{

+  struct dl_hwcaps_split split;

+

+  /* For used by the iterator implementation.  */

+  const char *mask;

+  uint32_t bitmask;

+};

+

+/* Prepare *S for iteration with _dl_hwcaps_split_masked.  Only HWCAP

+   names in SUBJECT whose bit is set in BITMASK and whose name is in

+   MASK will be returned.  SUBJECT must not contain empty HWCAP names.

+   If MASK is NULL, no name-based masking is applied.  Likewise for

+   BITMASK if BITMASK is -1 (infinite number of bits).  */

+static inline void

+_dl_hwcaps_split_masked_init (struct dl_hwcaps_split_masked *s,

+                              const char *subject,

+                              uint32_t bitmask, const char *mask)

+{

+  _dl_hwcaps_split_init (&s->split, subject);

+  s->bitmask = bitmask;

+  s->mask = mask;

+}

+

+/* Like _dl_hwcaps_split, but apply masking.  */

+_Bool _dl_hwcaps_split_masked (struct dl_hwcaps_split_masked *s)

+  attribute_hidden;

+

+/* Returns true if the colon-separated HWCAP list HWCAPS contains the

+   capability NAME (with length NAME_LENGTH).  If HWCAPS is NULL, the

+   function returns true.  */

+_Bool _dl_hwcaps_contains (const char *hwcaps, const char *name,

+                           size_t name_length) attribute_hidden;

+

+/* Colon-separated string of glibc-hwcaps subdirectories, without the

+   "glibc-hwcaps/" prefix.  The most preferred subdirectory needs to

+   be listed first.  Up to 32 subdirectories are supported, limited by

+   the width of the uint32_t mask.  */

+extern const char _dl_hwcaps_subdirs[] attribute_hidden;

+

+/* Returns a bitmap of active subdirectories in _dl_hwcaps_subdirs.

+   Bit 0 (the LSB) corresponds to the first substring in

+   _dl_hwcaps_subdirs, bit 1 to the second substring, and so on.

+   There is no direct correspondence between HWCAP bitmasks and this

+   bitmask.  */

+uint32_t _dl_hwcaps_subdirs_active (void) attribute_hidden;

+

+/* Returns a bitmask that marks the last ACTIVE subdirectories in a

+   _dl_hwcaps_subdirs_active string (containing SUBDIRS directories in

+   total) as active.  Intended for use in _dl_hwcaps_subdirs_active

+   implementations (if a contiguous tail of the list in

+   _dl_hwcaps_subdirs is selected).  */

+static inline uint32_t

+_dl_hwcaps_subdirs_build_bitmask (int subdirs, int active)

+{

+  /* Leading subdirectories that are not active.  */

+  int inactive = subdirs - active;

+  if (inactive == 32)

+    return 0;

+

+  uint32_t mask;

+  if (subdirs != 32)

+    mask = (1U << subdirs) - 1;

+  else

+    mask = -1;

+  return mask ^ ((1U << inactive) - 1);

+}

+

+#endif /* _DL_HWCAPS_H */

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

new file mode 100644

index 0000000000000000..95225e9f409ca229

--- /dev/null

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

@@ -0,0 +1,77 @@

+/* Hardware capability support for run-time dynamic loader.  String splitting.

+   Copyright (C) 2020 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 <dl-hwcaps.h>

+#include <stdbool.h>

+#include <string.h>

+

+_Bool

+_dl_hwcaps_split (struct dl_hwcaps_split *s)

+{

+  if (s->segment == NULL)

+    return false;

+

+  /* Skip over the previous segment.   */

+  s->segment += s->length;

+

+  /* Consume delimiters.  This also avoids returning an empty

+     segment.  */

+  while (*s->segment == ':')

+    ++s->segment;

+  if (*s->segment == '\0')

+    return false;

+

+  /* This could use strchrnul, but we would have to link the function

+     into ld.so for that.  */

+  const char *colon = strchr (s->segment, ':');

+  if (colon == NULL)

+    s->length = strlen (s->segment);

+  else

+    s->length = colon - s->segment;

+  return true;

+}

+

+_Bool

+_dl_hwcaps_split_masked (struct dl_hwcaps_split_masked *s)

+{

+  while (true)

+    {

+      if (!_dl_hwcaps_split (&s->split))

+        return false;

+      bool active = s->bitmask & 1;

+      s->bitmask >>= 1;

+      if (active && _dl_hwcaps_contains (s->mask,

+                                         s->split.segment, s->split.length))

+        return true;

+    }

+}

+

+_Bool

+_dl_hwcaps_contains (const char *hwcaps, const char *name, size_t name_length)

+{

+  if (hwcaps == NULL)

+    return true;

+

+  struct dl_hwcaps_split split;

+  _dl_hwcaps_split_init (&split, hwcaps);

+  while (_dl_hwcaps_split (&split))

+    if (split.length == name_length

+        && memcmp (split.segment, name, name_length) == 0)

+      return true;

+  return false;

+}

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

index d2be21ea7d1545fe..fee08d7816714178 100644

--- a/elf/dl-load.c

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

@@ -682,7 +682,9 @@ cache_rpath (struct link_map *l,

 void

-_dl_init_paths (const char *llp, const char *source)

+_dl_init_paths (const char *llp, const char *source,

+		const char *glibc_hwcaps_prepend,

+		const char *glibc_hwcaps_mask)

 {

   size_t idx;

   const char *strp;

@@ -697,7 +699,8 @@ _dl_init_paths (const char *llp, const char *source)

 #ifdef SHARED

   /* Get the capabilities.  */

-  capstr = _dl_important_hwcaps (&ncapstr, &max_capstrlen);

+  capstr = _dl_important_hwcaps (glibc_hwcaps_prepend, glibc_hwcaps_mask,

+				 &ncapstr, &max_capstrlen);

 #endif

   /* First set up the rest of the default search directory entries.  */

diff --git a/elf/dl-main.h b/elf/dl-main.h

index b51256d3b48230b0..566713a0d10cfdb7 100644

--- a/elf/dl-main.h

+++ b/elf/dl-main.h

@@ -84,6 +84,14 @@ struct dl_main_state

   /* The preload list passed as a command argument.  */

   const char *preloadarg;

+  /* Additional glibc-hwcaps subdirectories to search first.

+     Colon-separated list.  */

+  const char *glibc_hwcaps_prepend;

+

+  /* Mask for the internal glibc-hwcaps subdirectories.

+     Colon-separated list.  */

+  const char *glibc_hwcaps_mask;

+

   enum rtld_mode mode;

   /* True if any of the debugging options is enabled.  */

@@ -98,7 +106,8 @@ struct dl_main_state

 static inline void

 call_init_paths (const struct dl_main_state *state)

 {

-  _dl_init_paths (state->library_path, state->library_path_source);

+  _dl_init_paths (state->library_path, state->library_path_source,

+                  state->glibc_hwcaps_prepend, state->glibc_hwcaps_mask);

 }

 /* Print ld.so usage information and exit.  */

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

index fb9672367f8d6abd..34be8e5babfb6af3 100644

--- a/elf/dl-support.c

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

@@ -315,7 +315,10 @@ _dl_non_dynamic_init (void)

   /* Initialize the data structures for the search paths for shared

      objects.  */

-  _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH");

+  _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",

+		  /* No glibc-hwcaps selection support in statically

+		     linked binaries.  */

+		  NULL, NULL);

   /* Remember the last search directory added at startup.  */

   _dl_init_all_dirs = GL(dl_all_dirs);

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

index 796ad38b43c2211b..e22a9c39427187d1 100644

--- a/elf/dl-usage.c

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

@@ -83,7 +83,7 @@ print_search_path_for_help (struct dl_main_state *state)

 {

   if (__rtld_search_dirs.dirs == NULL)

     /* The run-time search paths have not yet been initialized.  */

-    _dl_init_paths (state->library_path, state->library_path_source);

+    call_init_paths (state);

   _dl_printf ("\nShared library search path:\n");

@@ -132,6 +132,67 @@ print_hwcap_1_finish (bool *first)

     _dl_printf (")\n");

 }

+/* Print the header for print_hwcaps_subdirectories.  */

+static void

+print_hwcaps_subdirectories_header (bool *nothing_printed)

+{

+  if (*nothing_printed)

+    {

+      _dl_printf ("\n\

+Subdirectories of glibc-hwcaps directories, in priority order:\n");

+      *nothing_printed = false;

+    }

+}

+

+/* Print the HWCAP name itself, indented.  */

+static void

+print_hwcaps_subdirectories_name (const struct dl_hwcaps_split *split)

+{

+  _dl_write (STDOUT_FILENO, "  ", 2);

+  _dl_write (STDOUT_FILENO, split->segment, split->length);

+}

+

+/* Print the list of recognized glibc-hwcaps subdirectories.  */

+static void

+print_hwcaps_subdirectories (const struct dl_main_state *state)

+{

+  bool nothing_printed = true;

+  struct dl_hwcaps_split split;

+

+  /* The prepended glibc-hwcaps subdirectories.  */

+  _dl_hwcaps_split_init (&split, state->glibc_hwcaps_prepend);

+  while (_dl_hwcaps_split (&split))

+    {

+      print_hwcaps_subdirectories_header (&nothing_printed);

+      print_hwcaps_subdirectories_name (&split);

+      bool first = true;

+      print_hwcap_1 (&first, true, "searched");

+      print_hwcap_1_finish (&first);

+    }

+

+  /* The built-in glibc-hwcaps subdirectories.  Do the filtering

+     manually, so that more precise diagnostics are possible.  */

+  uint32_t mask = _dl_hwcaps_subdirs_active ();

+  _dl_hwcaps_split_init (&split, _dl_hwcaps_subdirs);

+  while (_dl_hwcaps_split (&split))

+    {

+      print_hwcaps_subdirectories_header (&nothing_printed);

+      print_hwcaps_subdirectories_name (&split);

+      bool first = true;

+      print_hwcap_1 (&first, mask & 1, "supported");

+      bool listed = _dl_hwcaps_contains (state->glibc_hwcaps_mask,

+                                         split.segment, split.length);

+      print_hwcap_1 (&first, !listed, "masked");

+      print_hwcap_1 (&first, (mask & 1) && listed, "searched");

+      print_hwcap_1_finish (&first);

+      mask >>= 1;

+    }

+

+  if (nothing_printed)

+    _dl_printf ("\n\

+No subdirectories of glibc-hwcaps directories are searched.\n");

+}

+

 /* Write a list of hwcap subdirectories to standard output.  See

  _dl_important_hwcaps in dl-hwcaps.c.  */