elf: Add glibc-hwcaps subdirectory support to ld.so cache processing

This recognizes the DL_CACHE_HWCAP_EXTENSION flag in cache entries,
and picks the supported cache entry with the highest priority.

The elf/tst-glibc-hwcaps-prepend-cache test documents a non-desired
aspect of the current cache implementation: If the cache selects a DSO
that does not exist on disk, _dl_map_object falls back to open_path,
which may or may not find an alternative implementation.  This is an
existing limitation that also applies to the legacy hwcaps processing
for ld.so.cache.

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

1 files changed, 149 insertions, 0 deletions

diff --git a/elf/tst-glibc-hwcaps-prepend-cache.c b/elf/tst-glibc-hwcaps-prepend-cache.c
new file mode 100644
index 0000000000..40509cebe2
--- /dev/null
+++ b/elf/tst-glibc-hwcaps-prepend-cache.c
@@ -0,0 +1,149 @@
+/* Test that --glibc-hwcaps-prepend works, using dlopen and /etc/ld.so.cache.
+   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 <dlfcn.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/xdlfcn.h>
+#include <support/xunistd.h>
+
+/* Invoke /sbin/ldconfig with some error checking.  */
+static void
+run_ldconfig (void)
+{
+  char *command = xasprintf ("%s/ldconfig", support_install_rootsbindir);
+  TEST_COMPARE (system (command), 0);
+  free (command);
+}
+
+/* The library under test.  */
+#define SONAME "libmarkermod1.so"
+
+static int
+do_test (void)
+{
+  if (dlopen (SONAME, RTLD_NOW) != NULL)
+    FAIL_EXIT1 (SONAME " is already on the search path");
+
+  /* Install the default implementation of libmarkermod1.so.  */
+  xmkdirp ("/etc", 0777);
+  support_write_file_string ("/etc/ld.so.conf", "/glibc-test/lib\n");
+  xmkdirp ("/glibc-test/lib/glibc-hwcaps/prepend2", 0777);
+  xmkdirp ("/glibc-test/lib/glibc-hwcaps/prepend3", 0777);
+  {
+    char *src = xasprintf ("%s/elf/libmarkermod1-1.so", support_objdir_root);
+    support_copy_file (src, "/glibc-test/lib/" SONAME);
+    free (src);
+  }
+  run_ldconfig ();
+  {
+    /* The default implementation can now be loaded.  */
+    void *handle = xdlopen (SONAME, RTLD_NOW);
+    int (*marker1) (void) = xdlsym (handle, "marker1");
+    TEST_COMPARE (marker1 (), 1);
+    xdlclose (handle);
+  }
+
+  /* Add the first override to the directory that is searched last.  */
+  {
+    char *src = xasprintf ("%s/elf/libmarkermod1-2.so", support_objdir_root);
+    support_copy_file (src, "/glibc-test/lib/glibc-hwcaps/prepend2/"
+                       SONAME);
+    free (src);
+  }
+  {
+    /* This is still the first implementation.  The cache has not been
+       updated.  */
+    void *handle = xdlopen (SONAME, RTLD_NOW);
+    int (*marker1) (void) = xdlsym (handle, "marker1");
+    TEST_COMPARE (marker1 (), 1);
+    xdlclose (handle);
+  }
+  run_ldconfig ();
+  {
+    /* After running ldconfig, it is the second implementation.  */
+    void *handle = xdlopen (SONAME, RTLD_NOW);
+    int (*marker1) (void) = xdlsym (handle, "marker1");
+    TEST_COMPARE (marker1 (), 2);
+    xdlclose (handle);
+  }
+
+  /* Add the second override to the directory that is searched first.  */
+  {
+    char *src = xasprintf ("%s/elf/libmarkermod1-3.so", support_objdir_root);
+    support_copy_file (src, "/glibc-test/lib/glibc-hwcaps/prepend3/"
+                       SONAME);
+    free (src);
+  }
+  {
+    /* This is still the second implementation.  */
+    void *handle = xdlopen (SONAME, RTLD_NOW);
+    int (*marker1) (void) = xdlsym (handle, "marker1");
+    TEST_COMPARE (marker1 (), 2);
+    xdlclose (handle);
+  }
+  run_ldconfig ();
+  {
+    /* After running ldconfig, it is the third implementation.  */
+    void *handle = xdlopen (SONAME, RTLD_NOW);
+    int (*marker1) (void) = xdlsym (handle, "marker1");
+    TEST_COMPARE (marker1 (), 3);
+    xdlclose (handle);
+  }
+
+  /* Remove the second override again, without running ldconfig.
+     Ideally, this would revert to implementation 2.  However, in the
+     current implementation, the cache returns exactly one file name
+     which does not exist after unlinking, so the dlopen fails.  */
+  xunlink ("/glibc-test/lib/glibc-hwcaps/prepend3/" SONAME);
+  TEST_VERIFY (dlopen (SONAME, RTLD_NOW) == NULL);
+  run_ldconfig ();
+  {
+    /* After running ldconfig, the second implementation is available
+       once more.  */
+    void *handle = xdlopen (SONAME, RTLD_NOW);
+    int (*marker1) (void) = xdlsym (handle, "marker1");
+    TEST_COMPARE (marker1 (), 2);
+    xdlclose (handle);
+  }
+
+  return 0;
+}
+
+static void
+prepare (int argc, char **argv)
+{
+  const char *no_restart = "no-restart";
+  if (argc == 2 && strcmp (argv[1], no_restart) == 0)
+    return;
+  /* Re-execute the test with an explicit loader invocation.  */
+  execl (support_objdir_elf_ldso,
+         support_objdir_elf_ldso,
+         "--glibc-hwcaps-prepend", "prepend3:prepend2",
+         argv[0], no_restart,
+         NULL);
+  printf ("error: execv of %s failed: %m\n", argv[0]);
+  _exit (1);
+}
+
+#define PREPARE prepare
+#include <support/test-driver.c>