Fix case where IR file provides symbol visibility but replacement file does not.

In PR 22868, two IR files provide conflicting visibility for a symbol.
When a def with PROTECTED visibility is seen after a def with DEFAULT
visibility, gold does not override the visibility. Later, if the
replacement object define the symbol with DEFAULT visibility, the symbol
remains DEFAULT. This was caused by a recent change to allow multiply-defined
absolute symbols, combined with the fact that the plugin framework was using
SHN_ABS as the section index for placeholder symbols. The solution is to
use a real (but arbitrary) section index.

gold/
	PR gold/22868
	* plugin.cc (Sized_pluginobj::do_add_symbols): Use a real section
	index instead of SHN_ABS for defined symbols.
	* testsuite/Makefile.am (plugin_pr22868): New test case.
	* testsuite/Makefile.in: Regenerate
	* testsuite/plugin_pr22868.sh: New test script.
	* testsuite/plugin_pr22868_a.c: New source file.
	* testsuite/plugin_pr22868_b.c: New source file.

1 files changed, 39 insertions, 0 deletions

diff --git a/gold/testsuite/plugin_pr22868_b.c b/gold/testsuite/plugin_pr22868_b.c
new file mode 100644
index 00000000000..92d2145b2d8
--- /dev/null
+++ b/gold/testsuite/plugin_pr22868_b.c
@@ -0,0 +1,39 @@
+/* plugin_pr22868_b_ir.c -- a test case for the plugin API with GC.
+
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   Written by Cary Coutant <ccoutant@gmail.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.  */
+
+/* This file is compiled with -DIR to generate the .syms file,
+   and without -DIR for use as the replacement object.
+   The .syms file declares foo with protected visibility, but
+   the replacement file does not.  */
+
+#ifdef IR
+#define PROTECTED __attribute__ (( visibility ("protected") ))
+#else
+#define PROTECTED
+#endif
+
+int foo(int i) __attribute__ (( weak )) PROTECTED;
+
+int foo(int i)
+{
+  return i + 1;
+}