[PING^2][PATCH] [gdb/testsuite] Fix gdb.base/inline-frame-cycle-unwind.exp for s390x (alternative)

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

On 1/3/26 4:12 PM, Tom de Vries wrote:
> On 12/11/25 2:39 PM, Tom de Vries wrote:
>> 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.
>>

Ping^2.

Thanks,
- Tom

>> 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
>