[PATCH] [gdb/testsuite] Fix gdb.base/inline-frame-cycle-unwind.exp for s390x (alternative)

[Tom de Vries <tdevries@suse.de>]

With test-case gdb.base/inline-frame-cycle-unwind.exp on s390x-linux, I run
into:
...
 (gdb) bt^M
 #0  inline_func () at inline-frame-cycle-unwind.c:49^M
 #1  normal_func () at inline-frame-cycle-unwind.c:32^M
 #2  0x000000000100065c in inline_func () at inline-frame-cycle-unwind.c:45^M
 #3  normal_func () at inline-frame-cycle-unwind.c:32^M
 Backtrace stopped: previous frame identical to this frame (corrupt stack?)^M
 (gdb) FAIL: $exp: bt: cycle at level 5: backtrace when the unwind is broken \
   at frame 5
...

In contrast, on x86_64-linux, I get:
...
 (gdb) bt^M
 #0  inline_func () at inline-frame-cycle-unwind.c:49^M
 #1  normal_func () at inline-frame-cycle-unwind.c:32^M
 #2  0x0000000000401157 in inline_func () at inline-frame-cycle-unwind.c:45^M
 #3  normal_func () at inline-frame-cycle-unwind.c:32^M
 #4  0x0000000000401157 in inline_func () at inline-frame-cycle-unwind.c:45^M
 #5  normal_func () at inline-frame-cycle-unwind.c:32^M
 Backtrace stopped: previous frame identical to this frame (corrupt stack?)^M
 (gdb) PASS: $exp: bt: cycle at level 5: backtrace when the unwind is broken \
   at frame 5
...

AFAIU, the mechanism of the test is as follows: the custom unwinder produces the
frame-id for frame #5 at frame #4.  Consequently, when arriving at frame #5, a
cycle is detected.

[ It took me a while to understand this because of the following off-by-one
confusion: for frame #0, we get pending_frame.level() == 1.  So when
stop_at_level == 5, the custom unwinder calculates a frame-id for frame #4,
not frame #5.  But the frame-id it calculates is the one for frame #5, so
unwinding will stop at frame #5 because the frame-ids for frame #4 and
frame #5 are identical. ]

This relies on the test-case to calculate the offending frame-id, and the
problem on s390x is that that calculation is incorrect.

Fix this by using "maint print frame-id" to get all frame-ids, and using those
instead.

Tested on x86_64-linux and s390x-linux.
---
 .../gdb.base/inline-frame-cycle-unwind.exp          | 13 +++++++++++++
 gdb/testsuite/gdb.base/inline-frame-cycle-unwind.py |  8 +++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp b/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp
index 7fc47af624f..5c6504323ee 100644
--- a/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp
+++ b/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp
@@ -72,6 +72,19 @@ gdb_continue_to_breakpoint "stop at test breakpoint"
 gdb_test_no_output "source ${pyfile}"\
     "import python scripts"
 
+foreach_with_prefix n { 0 1 2 3 4 5 6 } {
+    set sp 0x0
+    set pc 0x0
+    gdb_test_multiple "maint print frame-id $n" "" {
+	-re -wrap "frame-id for frame #$n: {stack=($hex),code=($hex),.*}" {
+	    set sp $expect_out(1,string)
+	    set pc $expect_out(2,string)
+	    gdb_test_no_output "python frame_id_sp.append($sp)"
+	    gdb_test_no_output "python frame_id_pc.append($pc)"
+	}
+    }
+}
+
 # Test with and without filters.
 foreach bt_cmd { "bt" "bt -no-filters" } {
     with_test_prefix "$bt_cmd" {
diff --git a/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.py b/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.py
index 55dea989512..25a67b1a7c9 100644
--- a/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.py
+++ b/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.py
@@ -26,6 +26,9 @@ stop_at_level = None
 # function called recursively.
 stack_adjust = None
 
+frame_id_sp = []
+frame_id_pc = []
+
 
 class FrameId(object):
     def __init__(self, sp, pc):
@@ -55,9 +58,8 @@ class TestUnwinder(Unwinder):
         if stop_at_level not in [1, 3, 5]:
             raise gdb.GdbError("invalid stop_at_level")
 
-        sp_desc = pending_frame.architecture().registers().find("sp")
-        sp = pending_frame.read_register(sp_desc) + stack_adjust
-        pc = (gdb.lookup_symbol("normal_func"))[0].value().address
+        sp = frame_id_sp[stop_at_level]
+        pc = frame_id_pc[stop_at_level]
         unwinder = pending_frame.create_unwind_info(FrameId(sp, pc))
 
         for reg in pending_frame.architecture().registers("general"):

base-commit: 2271dee682787051c0628c869d7cdb220bdd0e67
-- 
2.51.0