PR symtab/14466: Work around PR libc/13097 "linux-vdso.so.1"

With upstream glibc, GDB prints:

  warning: Could not load shared library symbols for linux-vdso.so.1.
  Do you need "set solib-search-path" or "set sysroot"?

A bug's been filed for glibc a few years back:

  http://sourceware.org/bugzilla/show_bug.cgi?id=13097

but it's still not resolved.  It's not clear whether there's even
consensus that this is indeed a glibc bug.  It would actually be nice
if GDB also listed the vDSO in the shared library list, but there are
some design considerations with that:

 - the vDSO is mapped by the kernel, not userspace, therefore we
   should load its symbols right from the process's start of life,
   even before glibc / the userspace loader sets up the initial DSO
   list.  The program might even be using a custom loader or no
   loader.

 - that kind of hints at that solib.c should handle retrieving shared
   library lists from more than one source, and that symfile-mem.c's
   loading of the vDSO would be converted to load and relocate the
   vDSO's bfd behind the target_so_ops interface.

 - and then, once glibc links in the vDSO to its DSO list, we'd need
   to either:

    a) somehow hand over the vDSO from one target_so_ops to the other

    b) simply keep hiding glibc's entry.

And then b) seems the simplest.

With that in mind, this patch simply discards the vDSO from glibc's
reported shared library list.

We can match the vDSO address range with the addresses found iterating
the dynamic linker list, to tell which dynamic linker entry is the
vDSO.

Tested on x86_64 Fedora 20.

gdb/
2014-10-10  Jan Kratochvil  <jan.kratochvil@redhat.com>
	    Pedro Alves  <palves@redhat.com>

	PR symtab/14466
	* solib-svr4.c (svr4_read_so_list): Rename to ...
	(svr4_current_sos_1): ... this and change the function comment.
	(svr4_current_sos): New function.

gdb/testsuite/
2014-10-10  Jan Kratochvil  <jan.kratochvil@redhat.com>
	    Pedro Alves  <palves@redhat.com>

	PR symtab/14466
	* gdb.base/vdso-warning.c: New file.
	* gdb.base/vdso-warning.exp: New file.

3 files changed, 83 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index fac6e07..5578060 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2014-10-10  Jan Kratochvil  <jan.kratochvil@redhat.com>
+	    Pedro Alves  <palves@redhat.com>
+
+	PR symtab/14466
+	* gdb.base/vdso-warning.c: New file.
+	* gdb.base/vdso-warning.exp: New file.
+
 2014-10-02  Doug Evans  <dje@google.com>
 
 	* gdb.base/structs.c (main): Don't run forever.
diff --git a/gdb/testsuite/gdb.base/vdso-warning.c b/gdb/testsuite/gdb.base/vdso-warning.c
new file mode 100644
index 0000000..4b94803
--- /dev/null
+++ b/gdb/testsuite/gdb.base/vdso-warning.c
@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2014 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int
+main (void)
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/vdso-warning.exp b/gdb/testsuite/gdb.base/vdso-warning.exp
new file mode 100644
index 0000000..1f538fa
--- /dev/null
+++ b/gdb/testsuite/gdb.base/vdso-warning.exp
@@ -0,0 +1,54 @@
+# Copyright 2012-2014 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" ${testfile} $srcfile] } {
+    return -1
+}
+
+gdb_breakpoint "main"
+
+# At least some versions of Fedora/RHEL glibc have local patches that
+# hide the vDSO.  This lines re-exposes it.  See PR libc/13097,
+# comment 2.  There's no support for passing environment variables in
+# the remote protocol, but that's OK -- if we're testing against a
+# glibc that doesn't list the vDSO without this, the test should still
+# pass.
+gdb_test_no_output "set environment LD_DEBUG=unused"
+
+gdb_run_cmd
+
+set test "stop without warning"
+gdb_test_multiple "" $test {
+    -re "Could not load shared library symbols .*\r\n$gdb_prompt $" {
+	fail $test
+    }
+    -re "\r\nBreakpoint \[0-9\]+, main .*\r\n$gdb_prompt $" {
+	pass $test
+    }
+}
+
+# Extra testing in case the warning changes and we miss updating the
+# above.
+set test "no vdso without symbols is listed"
+gdb_test_multiple "info shared" $test {
+    -re "No\[^\r\n\]+linux-(vdso|gate).*$gdb_prompt $" {
+	fail $test
+    }
+    -re "$gdb_prompt $" {
+	pass $test
+    }
+}