Re: [PATCH v4 19/39] unwind_user/sframe: Add support for reading .sframe contents

Jens Remus
2025-01-28T10:54:30Z

On 28.01.2025 01:39, Andrii Nakryiko wrote:
> On Fri, Jan 24, 2025 at 1:41 PM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>> On Fri, Jan 24, 2025 at 10:02:46AM -0800, Andrii Nakryiko wrote:
>>> On Tue, Jan 21, 2025 at 6:32 PM Josh Poimboeuf <jpoimboe@kernel.org> wrote:

>>>> + fre_addr = sec->fres_start + fde->fres_off;
>>>> +
>>>> + for (i = 0; i < fde->fres_num; i++) {
>>>
>>> why not binary search? seem more logical to guard against cases with
>>> lots of FREs and be pretty fast in common case anyways.
>>
>> That would be nice, but the FREs are variable-sized and you don't know
>> how big one is until you start reading it.
>
> ah, another non-obvious thing, yeah... do you think it's worth fixing
> this and making FREs binary searchable in v3?
>
> Indu, do you have some stats on distribution of FRE count per FDE in practice?
>
> Tbh, FRE format is bothering me quite a lot... but let's discuss that
> in another thread with you and Indu

I would be interested to be part of that discussion. I could share some
preliminary stats from my s390 work.

Thanks and regards,
Jens
--
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@de.ibm.com

IBM

IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Böblingen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/