Fix for prologue processing on PowerPC

One of conditions in skip_prologue() was never visited if there was mflr
instruction that moves the link register to a register different than r0.
This condition expects non shifted value of `lr_reg`. Previously offset
of link register was never saved for registers different than r0.

gdb/ChangeLog:

2018-01-31  Nikola Prica  <nikola.prica@rt-rk.com>

	* rs6000-tdep.c (skip_prologue): Remove shifting for lr_reg and
	assign shifted lr_reg to fdata->lr_register when lr_reg is set.

gdb/testsuite/ChangeLog:

2018-01-31  Nikola Prica  <nikola.prica@rt-rk.com>

	* gdb.arch/powerpc-prologue-frame.s: New file.
	* gdb.arch/powerpc-prologue-frame.c: Likewise.
	* gdb.arch/powerpc-prologue-frame.exp: Likewise.

1 files changed, 41 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.arch/powerpc-prologue-frame.exp b/gdb/testsuite/gdb.arch/powerpc-prologue-frame.exp
new file mode 100644
index 0000000..d26314b
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/powerpc-prologue-frame.exp
@@ -0,0 +1,41 @@
+# Copyright 2018 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/>
+
+if {![istarget "powerpc-*-*"] } {
+    verbose "Skipping powerpc back trace test."
+    return
+}
+
+standard_testfile .c .S
+set binfile [standard_output_file ${testfile}]
+
+if {[gdb_compile \
+      [list ${srcdir}/${subdir}/$srcfile ${srcdir}/${subdir}/$srcfile2] \
+      "${binfile}" executable {}] != ""} {
+    untested "failed to build $binfile"
+    return -1
+}
+
+
+clean_restart ${binfile}
+
+if ![runto bar] {
+  untested "could not run to bar"
+  return -1
+}
+
+gdb_test "bt" \
+         "#0\[ \t\]*$hex in bar.*\r\n#1\[ \t\]*$hex in foo.*\r\n#2\[ \t\]*$hex in main.*" \
+         "Backtrace to the main frame"