Subject: [bug#44899] [PATCH 1/3] gnu: glibc: Load ${ORIGIN}/../etc/ld.so.cache when available.

From: Ludovic Courtès <[email-masked]>
Date: Fri, 27 Nov 2020 10:05:21 +0100

* gnu/packages/patches/glibc-dl-cache.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/base.scm (glibc)[source]: Remove 'snippet' and 'modules'.
---
 gnu/local.mk                              |   1 +
 gnu/packages/base.scm                     |  11 +-
 gnu/packages/patches/glibc-dl-cache.patch | 122 ++++++++++++++++++++++
 3 files changed, 124 insertions(+), 10 deletions(-)
 create mode 100644 gnu/packages/patches/glibc-dl-cache.patch

diff --git a/gnu/local.mk b/gnu/local.mk
index f9fed30a3f..82c3c608c6 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -1051,6 +1051,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/glibc-bootstrap-system-2.2.5.patch 	\
   %D%/packages/patches/glibc-bootstrap-system-2.16.0.patch 	\
   %D%/packages/patches/glibc-bootstrap-system.patch		\
+  %D%/packages/patches/glibc-dl-cache.patch			\
   %D%/packages/patches/glibc-hidden-visibility-ldconfig.patch	\
   %D%/packages/patches/glibc-hurd-clock_gettime_monotonic.patch	\
   %D%/packages/patches/glibc-hurd-clock_t_centiseconds.patch	\
diff --git a/gnu/packages/base.scm b/gnu/packages/base.scm
index bd352319a1..f8f4ae37fd 100644
--- a/gnu/packages/base.scm
+++ b/gnu/packages/base.scm
@@ -675,17 +675,8 @@ the store.")
             (sha256
              (base32
               "0di848ibffrnwq7g2dvgqrnn4xqhj3h96csn69q4da51ymafl9qn"))
-            (snippet
-             ;; Disable 'ldconfig' and /etc/ld.so.cache.  The latter is
-             ;; required on LFS distros to avoid loading the distro's libc.so
-             ;; instead of ours.
-             '(begin
-                (substitute* "sysdeps/unix/sysv/linux/configure"
-                  (("use_ldconfig=yes")
-                   "use_ldconfig=no"))
-                #t))
-            (modules '((guix build utils)))
             (patches (search-patches "glibc-ldd-x86_64.patch"
+                                     "glibc-dl-cache.patch"
                                      "glibc-hidden-visibility-ldconfig.patch"
                                      "glibc-versioned-locpath.patch"
                                      "glibc-allow-kernel-2.6.32.patch"
diff --git a/gnu/packages/patches/glibc-dl-cache.patch b/gnu/packages/patches/glibc-dl-cache.patch
new file mode 100644
index 0000000000..9d578bb3d9
--- /dev/null
+++ b/gnu/packages/patches/glibc-dl-cache.patch
@@ -0,0 +1,122 @@
+Read the shared library cache relative to $ORIGIN instead of reading
+from /etc/ld.so.cache.  Also arrange so that this cache takes
+precedence over RUNPATH.
+
+diff --git a/elf/dl-cache.c b/elf/dl-cache.c
+index 93d185e788..6a2989bd4c 100644
+--- a/elf/dl-cache.c
++++ b/elf/dl-cache.c
+@@ -171,6 +171,33 @@ _dl_cache_libcmp (const char *p1, const char *p2)
+   return *p1 - *p2;
+ }
+ 
++/* Special value representing the lack of an ld.so cache.  */
++static const char ld_so_cache_lacking[] = "/ld.so cache is lacking";
++
++/* Return the per-application ld.so cache, relative to $ORIGIN, or NULL if
++   that fails for some reason.  Do not return the system-wide LD_SO_CACHE
++   since on a foreign distro it would contain invalid information.  */
++static const char *
++ld_so_cache (void)
++{
++  static const char *loader_cache;
++
++  if (loader_cache == NULL)
++    {
++      const char suffix[] = "/../etc/ld.so.cache";
++      const char *origin = _dl_get_origin ();
++
++      /* Note: We can't use 'malloc' because it can be interposed.  */
++      char *cache = alloca (strlen (origin) + sizeof suffix);
++
++      strcpy (cache, origin);
++      strcat (cache, suffix);
++
++      loader_cache = __strdup (cache) ?: ld_so_cache_lacking;
++    }
++
++  return loader_cache;
++}
+ 
+ /* Look up NAME in ld.so.cache and return the file name stored there, or null
+    if none is found.  The cache is loaded if it was not already.  If loading
+@@ -190,12 +217,15 @@ _dl_load_cache_lookup (const char *name)
+ 
+   /* Print a message if the loading of libs is traced.  */
+   if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
+-    _dl_debug_printf (" search cache=%s\n", LD_SO_CACHE);
++    _dl_debug_printf (" search cache=%s\n", ld_so_cache ());
++
++  if (__glibc_unlikely (ld_so_cache () == ld_so_cache_lacking))
++    return NULL;
+ 
+   if (cache == NULL)
+     {
+       /* Read the contents of the file.  */
+-      void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
++      void *file = _dl_sysdep_read_whole_file (ld_so_cache (), &cachesize,
+ 					       PROT_READ);
+ 
+       /* We can handle three different cache file formats here:
+diff --git a/elf/dl-load.c b/elf/dl-load.c
+index f3201e7c14..a69aec3428 100644
+--- a/elf/dl-load.c
++++ b/elf/dl-load.c
+@@ -2152,28 +2152,6 @@ _dl_map_object (struct link_map *loader, const char *name,
+ 			loader ?: GL(dl_ns)[LM_ID_BASE]._ns_loaded,
+ 			LA_SER_LIBPATH, &found_other_class);
+ 
+-      /* Look at the RUNPATH information for this binary.  */
+-      if (fd == -1 && loader != NULL
+-	  && cache_rpath (loader, &loader->l_runpath_dirs,
+-			  DT_RUNPATH, "RUNPATH"))
+-	fd = open_path (name, namelen, mode,
+-			&loader->l_runpath_dirs, &realname, &fb, loader,
+-			LA_SER_RUNPATH, &found_other_class);
+-
+-      if (fd == -1)
+-        {
+-          realname = _dl_sysdep_open_object (name, namelen, &fd);
+-          if (realname != NULL)
+-            {
+-              fd = open_verify (realname, fd,
+-                                &fb, loader ?: GL(dl_ns)[nsid]._ns_loaded,
+-                                LA_SER_CONFIG, mode, &found_other_class,
+-                                false);
+-              if (fd == -1)
+-                free (realname);
+-            }
+-        }
+-
+ #ifdef USE_LDCONFIG
+       if (fd == -1
+ 	  && (__glibc_likely ((mode & __RTLD_SECURE) == 0)
+@@ -2232,6 +2210,28 @@ _dl_map_object (struct link_map *loader, const char *name,
+ 	}
+ #endif
+ 
++      /* Look at the RUNPATH information for this binary.  */
++      if (fd == -1 && loader != NULL
++	  && cache_rpath (loader, &loader->l_runpath_dirs,
++			  DT_RUNPATH, "RUNPATH"))
++	fd = open_path (name, namelen, mode,
++			&loader->l_runpath_dirs, &realname, &fb, loader,
++			LA_SER_RUNPATH, &found_other_class);
++
++      if (fd == -1)
++        {
++          realname = _dl_sysdep_open_object (name, namelen, &fd);
++          if (realname != NULL)
++            {
++              fd = open_verify (realname, fd,
++                                &fb, loader ?: GL(dl_ns)[nsid]._ns_loaded,
++                                LA_SER_CONFIG, mode, &found_other_class,
++                                false);
++              if (fd == -1)
++                free (realname);
++            }
++        }
++
+       /* Finally, try the default path.  */
+       if (fd == -1
+ 	  && ((l = loader ?: GL(dl_ns)[nsid]._ns_loaded) == NULL
-- 
2.29.2