Re: [PATCH v4 1/2] Change calculation of frame_id by amd64 epilogue unwinder

[Bruno Larsen <blarsen@redhat.com>]

On 25/10/2022 15:44, Simon Marchi wrote:
> On 10/5/22 06:38, Bruno Larsen via Gdb-patches wrote:
>> When GDB is stopped at a ret instruction and no debug information is
>> available for unwinding, GDB defaults to the amd64 epilogue unwinder, to
>> be able to generate a decent backtrace. However, when calculating the
>> frame id, the epilogue unwinder generates information as if the return
>> instruction was the whole frame.
>>
>> This was an issue especially when attempting to reverse debug, as GDB
>> would place a step_resume_breakpoint from the epilogue of a function if
>> we were to attempt to skip that function, and this breakpoint should
>> ideally have the current function's frame_id to avoid other problems
>> such as PR record/16678.
>>
>> This commit changes the frame_id calculation for the amd64 epilogue,
>> so that it is always the same as the dwarf2 unwinder's frame_id.
>>
>> It also adds a test to confirm that the frame_id will be the same,
>> regardless of using the epilogue unwinder or not, thanks to Andrew
>> Burgess.
>>
>> Co-Authored-By: Andrew Burgess <aburgess@redhat.com>
>> ---
>>   gdb/amd64-tdep.c                              |  10 +-
>>   .../gdb.base/unwind-on-each-insn-foo.c        |  22 +++
>>   gdb/testsuite/gdb.base/unwind-on-each-insn.c  |  25 +++
>>   .../gdb.base/unwind-on-each-insn.exp          | 154 ++++++++++++++++++
>>   4 files changed, 206 insertions(+), 5 deletions(-)
>>   create mode 100644 gdb/testsuite/gdb.base/unwind-on-each-insn-foo.c
>>   create mode 100644 gdb/testsuite/gdb.base/unwind-on-each-insn.c
>>   create mode 100644 gdb/testsuite/gdb.base/unwind-on-each-insn.exp
> Hi Bruno,
>
> On Ubuntu 22.04, I can get this new test to fail quite reliably with:
>
>      $ taskset -c 1 make check TESTS="gdb.base/unwind-on-each-insn.exp" RUNTESTFLAGS="--target_board=native-gdbserver"
>
> Can you give it a try?

Hi Simon,

I'll take a look, thanks for bringing this to my attention!

Cheers,
Bruno

>
> Simon
>