Add option --weak-unresolved-symbols to treat unresolved as weak references.

This patch adds option --weak-unresolved-symbols to treat unresolved symbols as
weak references.  This is helpful when we want the link to succeed with unresolved
symbols and the dynamic loader to not complain at run-time.  Option
--warn-unresolved-symbols lets the link succeed but could fail at run-time with
unresolved symbol warnings especially when the unresolved symbols have GOT entries
and dynamic relocations against them, like when -fPIE is used.

2015-04-23  Sriraman Tallam  <tmsriram@google.com>
	* options.h (--weak-unresolved-symbols): New option.
	* symtab.cc (Symbol_table::sized_write_globals): Change symbol
	binding to weak with new option.
	* symtab.h (is_weak_undefined): Check for new option.
	(is_strong_undefined): Check for new option.
	* testsuite/Makefile.am (weak_unresolved_symbols_test): New test.
	* testsuite/Makefile.in: Regenerate.
	* testsuite/weak_unresolved_symbols_test.cc: New file.

1 files changed, 45 insertions, 0 deletions

diff --git a/gold/testsuite/weak_unresolved_symbols_test.cc b/gold/testsuite/weak_unresolved_symbols_test.cc
new file mode 100644
index 0000000..ec2c462
--- /dev/null
+++ b/gold/testsuite/weak_unresolved_symbols_test.cc
@@ -0,0 +1,45 @@
+// weak_unresolved_symbols_test.cc -- a test case for gold
+
+// Copyright (C) 2015 Free Software Foundation, Inc.
+// Written by Sriraman Tallam <tmsriram@google.com>.
+
+// This file is part of gold.
+
+// 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, write to the Free Software
+// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
+// MA 02110-1301, USA.
+
+// Test --weak-unresolved-symbols.  Symbol foo remains unresolved but
+// with -fPIE, needs a GOT entry and has a dynsym entry and a dynamic
+// relocation against it created.  This  will fail to link and run without
+// --weak-unresolved-symbols.  With --warn-unresolved-symbols, it will link
+// but the dynamic linker will complain that foo(_Z3foov) is unresolved.
+
+extern int foo();
+
+int bar() {
+  return 0;
+}
+
+int (*p)() = &bar;
+
+int main() {
+  if (p == &foo)
+    {
+      foo();
+    }
+  else
+    (*p)();
+  return 0;
+}