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

[Simon Marchi <simark@simark.ca>]

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?

Simon