New ld.so argument --inhibit-ldcache to disable ld.so.cache lookup

It may sometimes be desirable to make the dynamic linker only pick up
libraries from the library path and rpath and not look at the
ld.so.cache that ldconfig generates. An example of such a use case is
the glibc testsuite where the dynamic linker must not be influenced by
any external paths or caches.

This change adds a new option --inhibit-ldcache that when used, tells
the dynamic linker to not use ld.so.cache even if it is available.

6 files changed, 31 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index cede7b8ee3..80b38fc2ac 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2012-04-10  Siddhesh Poyarekar  <siddhesh@redhat.com>
+
+	* elf/dl-support.c (_dl_inhibit_cache): New variable.
+	* elf/rtld.c (_rtld_global_ro): New member _dl_inhibit_cache.
+	(dl_main): Handle --inhibit-cache.
+	* sysdeps/generic/ldsodefs.h (struct rtld_global_ro): New member
+	_dl_inhibit_cache.
+	* elf/dl-load.c (_dl_map_object): Use it.
+	* elf/Makefile: Define SYSCONFDIR when building rtld.c.
+
 2012-04-09  Joseph Myers  <joseph@codesourcery.com>
 
 	[BZ #13872]
diff --git a/elf/Makefile b/elf/Makefile
index 59a3936a1b..a77e792cb4 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -1,4 +1,4 @@
-# Copyright (C) 1995-2011, 2012 Free Software Foundation, Inc.
+# Copyright (C) 1995-2012 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
@@ -419,6 +419,7 @@ CFLAGS-ldconfig.c = $(SYSCONF-FLAGS) -D'LIBDIR="$(libdir)"' \
 		    -D'SLIBDIR="$(slibdir)"' -DIS_IN_ldconfig=1
 CFLAGS-dl-cache.c = $(SYSCONF-FLAGS)
 CFLAGS-cache.c = $(SYSCONF-FLAGS)
+CFLAGS-rtld.c = $(SYSCONF-FLAGS)
 
 CPPFLAGS-.os += $(if $(filter $(@F),$(patsubst %,%.os,$(all-rtld-routines))),-DNOT_IN_libc=1 -DIS_IN_rtld=1)
 
diff --git a/elf/dl-load.c b/elf/dl-load.c
index 41d48ee138..fe83f87eb9 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1,5 +1,5 @@
 /* Map in a shared object's segments from the file.
-   Copyright (C) 1995-2007, 2009, 2010, 2011 Free Software Foundation, Inc.
+   Copyright (C) 1995-2012 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
@@ -2194,7 +2194,8 @@ _dl_map_object (struct link_map *loader, const char *name,
 
       if (fd == -1
 	  && (__builtin_expect (! (mode & __RTLD_SECURE), 1)
-	      || ! INTUSE(__libc_enable_secure)))
+	      || ! INTUSE(__libc_enable_secure))
+	  && __builtin_expect (GLRO(dl_inhibit_cache) == 0, 1))
 	{
 	  /* Check the list of libraries in the file /etc/ld.so.cache,
 	     for compatibility with Linux's ldconfig program.  */
diff --git a/elf/dl-support.c b/elf/dl-support.c
index 565f342e6b..a0f2122071 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -1,5 +1,5 @@
 /* Support for dynamic linking code in static libc.
-   Copyright (C) 1996-2008,2009,2010,2011 Free Software Foundation, Inc.
+   Copyright (C) 1996-2012 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
@@ -107,6 +107,8 @@ void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
 
 size_t _dl_pagesize = EXEC_PAGESIZE;
 
+int _dl_inhibit_cache;
+
 unsigned int _dl_osversion;
 
 /* All known directories in sorted order.  */
diff --git a/elf/rtld.c b/elf/rtld.c
index 0362b14968..88a340d1ee 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -161,6 +161,7 @@ struct rtld_global_ro _rtld_global_ro attribute_relro =
     ._dl_fpu_control = _FPU_DEFAULT,
     ._dl_pointer_guard = 1,
     ._dl_pagesize = EXEC_PAGESIZE,
+    ._dl_inhibit_cache = 0,
 
     /* Function pointers.  */
     ._dl_debug_printf = _dl_debug_printf,
@@ -973,6 +974,13 @@ dl_main (const ElfW(Phdr) *phdr,
 	    --_dl_argc;
 	    ++INTUSE(_dl_argv);
 	  }
+	else if (! strcmp (INTUSE(_dl_argv)[1], "--inhibit-cache"))
+	  {
+	    GLRO(dl_inhibit_cache) = 1;
+	    ++_dl_skip_args;
+	    --_dl_argc;
+	    ++INTUSE(_dl_argv);
+	  }
 	else if (! strcmp (INTUSE(_dl_argv)[1], "--library-path")
 		 && _dl_argc > 2)
 	  {
@@ -1022,6 +1030,7 @@ of this helper program; chances are you did not intend to run this program.\n\
   --list                list all dependencies and how they are resolved\n\
   --verify              verify that given object really is a dynamically linked\n\
 			object we can handle\n\
+  --inhibit-cache       Do not use " LD_SO_CACHE "\n\
   --library-path PATH   use given PATH instead of content of the environment\n\
 			variable LD_LIBRARY_PATH\n\
   --inhibit-rpath LIST  ignore RUNPATH and RPATH information in object names\n\
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 9955430e3c..602b429cea 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -1,5 +1,5 @@
 /* Run-time dynamic linker data structures for loaded ELF shared objects.
-   Copyright (C) 1995-2009, 2010, 2011, 2012 Free Software Foundation, Inc.
+   Copyright (C) 1995-2012 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
@@ -560,6 +560,9 @@ struct rtld_global_ro
   /* Cached value of `getpagesize ()'.  */
   EXTERN size_t _dl_pagesize;
 
+  /* Do we read from ld.so.cache?  */
+  EXTERN int _dl_inhibit_cache;
+
   /* Copy of the content of `_dl_main_searchlist' at startup time.  */
   EXTERN struct r_scope_elem _dl_initial_searchlist;