Re: [PATCH v2 3/3] x86: prefer shadow stack for producing call traces

[Jan Beulich <jbeulich@suse.com>]

On 08.04.2026 19:53, Andrew Cooper wrote:
> On 08/04/2026 1:23 pm, Jan Beulich wrote:
>> Shadow stacks contain little more than return addresses, and they in
>> particular allow precise call traces also without FRAME_POINTER.
> 
> Do you have an example of what such a backtrace now looks like ?

(XEN) Xen call trace:
(XEN)    [<ffff82d04032d730>] R extable.c#search_one_extable+0x70/0x73
(XEN)    [<ffff82d04032d802>] C search_exception_table+0xc2/0x177
(XEN)    [<ffff82d040358378>] C traps.c#extable_fixup.isra.0+0x18/0x6c
(XEN)    [<ffff82d040358e3b>] C do_invalid_op+0xab/0x106
(XEN)    [<ffff82d040201d98>] C x86_64/entry.S#handle_exception_saved+0x88/0xf4
(XEN)    [<ffff82d07fffe044>] E ffff82d07fffe044
(XEN)    [<ffff82d040412db0>] C stub_selftest+0xd0/0x168
(XEN)    [<ffff82d0403508d6>] C setup.c#init_done+0x116/0x15a

Note how both the stub entry and stub_selftest() as its caller are
present here. The stub entry is missing when FRAME_POINTER=n (albeit
we could teach that code to recognize it), while the stub_selftest()
entry is missing when FRAME_POINTER=y (and we can't do anything about
this unless we wanted to add frame setup to stub generation).

Jan