PPC64: Fix gdb.arch/ppc64-atomic-inst.exp with displaced stepping

The ppc64 displaced step code can't handle atomic sequences.  Fallback
to stepping over the breakpoint in-line if we detect one.

gdb/ChangeLog:
2015-08-07  Pedro Alves  <palves@redhat.com>

	* infrun.c (displaced_step_prepare_throw): Return -1 if
	gdbarch_displaced_step_copy_insn returns NULL.  Update intro
	comment.
	* rs6000-tdep.c (LWARX_MASK, LWARX_INSTRUCTION, LDARX_INSTRUCTION)
	(STWCX_MASK, STWCX_INSTRUCTION, STDCX_INSTRUCTION): Move higher up
	in file.
	(ppc_displaced_step_copy_insn): New function.
	(ppc_displaced_step_fixup): Update comment.
	(rs6000_gdbarch_init): Install ppc_displaced_step_copy_insn as
	gdbarch_displaced_step_copy_insn hook.
	* gdbarch.sh (displaced_step_copy_insn): Document what happens on
	NULL return.
	* gdbarch.h: Regenerate.

gdb/testsuite/ChangeLog:
2015-08-07  Pedro Alves  <palves@redhat.com>

	* gdb.arch/ppc64-atomic-inst.exp (do_test): New procedure, move
	tests here.
	(top level): Run do_test with and without displaced stepping.

2 files changed, 38 insertions, 18 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index cb69f08..813b249 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,11 @@
 2015-08-07  Pedro Alves  <palves@redhat.com>
 
+	* gdb.arch/ppc64-atomic-inst.exp (do_test): New procedure, move
+	tests here.
+	(top level): Run do_test with and without displaced stepping.
+
+2015-08-07  Pedro Alves  <palves@redhat.com>
+
 	* gdb.base/valgrind-disp-step.c: New file.
 	* gdb.base/valgrind-disp-step.exp: New file.
 
diff --git a/gdb/testsuite/gdb.arch/ppc64-atomic-inst.exp b/gdb/testsuite/gdb.arch/ppc64-atomic-inst.exp
index d251425..08518fb 100644
--- a/gdb/testsuite/gdb.arch/ppc64-atomic-inst.exp
+++ b/gdb/testsuite/gdb.arch/ppc64-atomic-inst.exp
@@ -32,27 +32,41 @@ if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile} {debug quiet}]
     return -1
 }
 
-if ![runto_main] then {
-    untested "could not run to main"
-    return -1
-}
+# The test proper.  DISPLACED is true if we should try with displaced
+# stepping.
+proc do_test { displaced } {
+    global decimal hex
+
+    if ![runto_main] then {
+	untested "could not run to main"
+	return -1
+    }
+
+    gdb_test_no_output "set displaced-stepping $displaced"
 
-set bp1 [gdb_get_line_number "lwarx"]
-gdb_breakpoint "$bp1" "Breakpoint $decimal at $hex" \
-  "Set the breakpoint at the start of the lwarx/stwcx sequence"
+    set bp1 [gdb_get_line_number "lwarx"]
+    gdb_breakpoint "$bp1" "Breakpoint $decimal at $hex" \
+	"Set the breakpoint at the start of the lwarx/stwcx sequence"
 
-set bp2 [gdb_get_line_number "ldarx"]
-gdb_breakpoint "$bp2" "Breakpoint $decimal at $hex" \
-  "Set the breakpoint at the start of the ldarx/stdcx sequence"
+    set bp2 [gdb_get_line_number "ldarx"]
+    gdb_breakpoint "$bp2" "Breakpoint $decimal at $hex" \
+	"Set the breakpoint at the start of the ldarx/stdcx sequence"
 
-gdb_test continue "Continuing.*Breakpoint $decimal.*" \
-  "Continue until lwarx/stwcx start breakpoint"
+    gdb_test continue "Continuing.*Breakpoint $decimal.*" \
+	"Continue until lwarx/stwcx start breakpoint"
 
-gdb_test nexti "bne.*1b" \
-  "Step through the lwarx/stwcx sequence"
+    gdb_test nexti "bne.*1b" \
+	"Step through the lwarx/stwcx sequence"
 
-gdb_test continue "Continuing.*Breakpoint $decimal.*" \
-  "Continue until ldarx/stdcx start breakpoint"
+    gdb_test continue "Continuing.*Breakpoint $decimal.*" \
+	"Continue until ldarx/stdcx start breakpoint"
 
-gdb_test nexti "bne.*1b" \
-  "Step through the ldarx/stdcx sequence"
+    gdb_test nexti "bne.*1b" \
+	"Step through the ldarx/stdcx sequence"
+}
+
+foreach displaced { "off" "on" } {
+    with_test_prefix "displaced=$displaced" {
+	do_test $displaced
+    }
+}