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.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+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.
+
 2018-01-31  Pedro Alves  <palves@redhat.com>
 
 	* darwin-nat.c (darwin_interrupt): Remove ptid_t parameter.

gdb/rs6000-tdep.c

@@ -1654,7 +1654,7 @@ skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc, CORE_ADDR lim_pc,
 	     remember just the first one, but skip over additional
 	     ones.  */
 	  if (lr_reg == -1)
-	    lr_reg = (op & 0x03e00000) >> 21;
+	    lr_reg = (op & 0x03e00000);
           if (lr_reg == 0)
             r0_contains_arg = 0;
 	  continue;
@@ -2180,7 +2180,7 @@ skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc, CORE_ADDR lim_pc,
 #endif /* 0 */
 
   if (pc == lim_pc && lr_reg >= 0)
-    fdata->lr_register = lr_reg;
+    fdata->lr_register = lr_reg >> 21;
 
   fdata->offset = -fdata->offset;
   return last_prologue_pc;

gdb/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+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.
+
 2018-01-31  Joel Brobecker  <brobecker@adacore.com>
 
 	* testsuite/gdb.ada/dyn_stride.exp: Add "print a1(1)@3" test.

gdb/testsuite/gdb.arch/powerpc-prologue-frame.S

@@ -0,0 +1,35 @@
+/* This test is part of GDB, the GNU debugger.
+
+   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/>.  */
+
+#include <ppc-asm.h>
+
+FUNC_START(foo)
+	stwu 1,-32(1)
+	mflr 3
+	stw 3,36(1)
+	stw 31,28(1)
+	mr 31,1
+	bl bar
+	mr 9,3
+	mr 3,9
+	addi 11,31,32
+	lwz 0,4(11)
+	mtlr 0
+	lwz 31,-4(11)
+	mr 1,11
+	blr
+FUNC_END(foo)

gdb/testsuite/gdb.arch/powerpc-prologue-frame.c

@@ -0,0 +1,28 @@
+/* This test is part of GDB, the GNU debugger.
+
+   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/>.  */
+
+int bar()
+{
+  return 0;
+}
+
+int foo();
+
+int main(void)
+{
+  return foo();
+}

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"