http://sourceware.org/ml/gdb-patches/2009-10/msg00142.html
Subject: [patch] Fix GNU/Linux core open: Can't read pathname for load map:  Input/output error.

Hi,

GDB currently always prints on loading a core file:
	warning: Can't read pathname for load map: Input/output error.

The patch is not nice but it was WONTFIXed on the glibc side in:
	http://sourceware.org/ml/libc-alpha/2009-10/msg00001.html

The same message in GDB PR 8882 and glibc PR 387 was for ld-linux.so.2 l_name
but that one is now ignored thanks to IGNORE_FIRST_LINK_MAP_ENTRY.

This fix is intended for Linux system vDSO l_name which is a second entry in
the DSO list.

Regression tested on {x86_86,x86_64-m32,i686}-fedora11-linux-gnu.


Thanks,
Jan


gdb/
2009-10-06  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Do not print false warning on reading core file with vDSO on GNU/Linux.
	* solib-svr4.c (svr4_current_sos): Suppress the warning if
	MASTER_SO_LIST is still NULL.
	* solib.c (update_solib_list): New variable saved_so_list_head.
	Conditionally restart the function.

[ Context backport.  ]

Index: gdb-7.3.50.20110722/gdb/solib-svr4.c
===================================================================
--- gdb-7.3.50.20110722.orig/gdb/solib-svr4.c	2011-07-22 19:26:46.000000000 +0200
+++ gdb-7.3.50.20110722/gdb/solib-svr4.c	2011-07-22 19:29:36.000000000 +0200
@@ -1197,8 +1197,18 @@ svr4_current_sos (void)
 	  target_read_string (lm_name (new), &buffer,
 			      SO_NAME_MAX_PATH_SIZE - 1, &errcode);
 	  if (errcode != 0)
-	    warning (_("Can't read pathname for load map: %s."),
-		     safe_strerror (errcode));
+	    {
+	      /* During the first ever DSO list reading some strings may be
+		 unreadable as residing in the ld.so readonly memory not being
+		 present in a dumped core file.  Delay the error check after
+		 the first pass of DSO list scanning when ld.so should be
+		 already mapped in and all the DSO list l_name memory gets
+		 readable.  */
+
+	      if (master_so_list () != NULL)
+		warning (_("Can't read pathname for load map: %s."),
+			 safe_strerror (errcode));
+	    }
 	  else
 	    {
 	      struct build_id *build_id;
Index: gdb-7.3.50.20110722/gdb/solib.c
===================================================================
--- gdb-7.3.50.20110722.orig/gdb/solib.c	2011-06-30 21:29:54.000000000 +0200
+++ gdb-7.3.50.20110722/gdb/solib.c	2011-07-22 19:29:10.000000000 +0200
@@ -706,6 +706,7 @@ update_solib_list (int from_tty, struct 
   struct target_so_ops *ops = solib_ops (target_gdbarch);
   struct so_list *inferior = ops->current_sos();
   struct so_list *gdb, **gdb_link;
+  struct so_list *saved_so_list_head = so_list_head;
 
   /* We can reach here due to changing solib-search-path or the
      sysroot, before having any inferior.  */
@@ -846,6 +847,12 @@ update_solib_list (int from_tty, struct 
 	  observer_notify_solib_loaded (i);
 	}
 
+      /* If this was the very first DSO list scan and we possibly read in ld.so
+	 recheck all the formerly unreadable DSO names strings.  */
+
+      if (saved_so_list_head == NULL && so_list_head != NULL)
+	return update_solib_list (from_tty, target);
+
       /* If a library was not found, issue an appropriate warning
 	 message.  We have to use a single call to warning in case the
 	 front end does something special with warnings, e.g., pop up