[PATCH v2] Skip vDSO when reading SO list (PR 8882)

[Andreas Arnez <arnez@linux.vnet.ibm.com>]

Suppress the warning when the vDSO's pathname from the SO list in a core
file can not be accessed.  The glibc's dynamic loader uses empty-string
literals for both the executable as well as the vDSO, and the compiler
collates both of them to a single string literal.  Thus the vDSO's
l_name address matches the main executable's.  This property is used as
a criteria for identifying and silently skipping the vDSO.

This version includes a small test case and follows Jan's proposal of
moving the suppression logic after the pathname read has already failed.

OK to apply?


ChangeLog:
2013-09-24  Andreas Arnez  <arnez@linux.vnet.ibm.com>

	* solib-svr4.c (svr4_read_so_list): Skip the vDSO when reading
	link map entries.

testsuite/ChangeLog:
2013-09-24  Andreas Arnez  <arnez@linux.vnet.ibm.com>

	* gdb.base/corefile.exp: Add a check to assure warning-free
	core-file load.

Index: gdb/gdb/solib-svr4.c
===================================================================
--- gdb.orig/gdb/solib-svr4.c
+++ gdb/gdb/solib-svr4.c
@@ -1310,6 +1310,7 @@ static int
 svr4_read_so_list (CORE_ADDR lm, CORE_ADDR prev_lm,
 		   struct so_list ***link_ptr_ptr, int ignore_first)
 {
+  struct so_list *first = NULL;
   CORE_ADDR next_lm;
 
   for (; lm != 0; prev_lm = lm, lm = next_lm)
@@ -1349,6 +1350,7 @@ svr4_read_so_list (CORE_ADDR lm, CORE_AD
 	{
 	  struct svr4_info *info = get_svr4_info ();
 
+	  first = new;
 	  info->main_lm_addr = new->lm_info->lm_addr;
 	  do_cleanups (old_chain);
 	  continue;
@@ -1359,8 +1361,16 @@ svr4_read_so_list (CORE_ADDR lm, CORE_AD
 			  SO_NAME_MAX_PATH_SIZE - 1, &errcode);
       if (errcode != 0)
 	{
-	  warning (_("Can't read pathname for load map: %s."),
-		   safe_strerror (errcode));
+	  /* If this entry's l_name address matches that of the
+	     inferior executable, then this is not a normal shared
+	     object, but (most likely) a vDSO.  In this case, silently
+	     skip it; otherwise emit a warning. */
+	  if (! (first != NULL
+		 && new->lm_info->l_name == first->lm_info->l_name))
+	    {
+	      warning (_("Can't read pathname for load map: %s."),
+		       safe_strerror (errcode));
+	    }
 	  do_cleanups (old_chain);
 	  continue;
 	}
Index: gdb/gdb/testsuite/gdb.base/corefile.exp
===================================================================
--- gdb.orig/gdb/testsuite/gdb.base/corefile.exp
+++ gdb/gdb/testsuite/gdb.base/corefile.exp
@@ -255,3 +255,19 @@ if ![is_remote target] {
 
     gdb_exit
 }
+
+# Test warning-free core file load.  E.g., a Linux vDSO used to
+# trigger this warning:
+#     warning: Can't read pathname for load map: Input/output error.
+
+clean_restart ${testfile}
+
+set test "core-file warning-free"
+gdb_test_multiple "core-file $corefile" $test {
+    -re "warning: .*\r\n.*\r\n$gdb_prompt $" {
+	fail $test
+    }
+    -re "\r\n$gdb_prompt $" {
+	pass $test
+    }
+}