ktrace produces a ktrace.out file in $PWD, kdump turns that into a textual 
list of system calls

if you get an "illegal instruction" trap, there should be something in 
there showing whether it's due to BTCFI or not

ktrace/kdump don't use debug symbols

-- 
  Sent from a phone, apologies for poor formatting.

On 12 November 2025 04:59:35 Walter Alejandro Iglesias <wai@roquesor.com> 
wrote:

> On Sat, Nov 08, 2025 at 11:04:55AM +0000, Stuart Henderson wrote:
>>>> It is IBT machine.
>>>
>>> Sorry, what does IBT stands for?
>>
>> indirect branch tracking, part of the control-flow enforcement features
>> on 11th gen/newer intel cpus. apple M2 has similar. if program code makes
>> an indirect jump, it will trap on SIGILL unless the jump target has a
>> specific opcode stored at that location.
>>
>> our compilers in base add this automatically, but asm code needs manual
>> changes if it doesn't already handle this.
>>
>> something changed in the FFmpeg 8 update that is triggering this in the
>> libraries; previously /usr/local/bin/ffmpeg was tripping it but we
>> didn't have such a problem with the libraries.
>>
>> if you hit SIGILL on amd64 with IBT in the dmesg cpu attach line, run
>> the program under ktrace, then kdump | grep SIGILL, look for a line like
>>
>> 1020 xfreerdp PSIG  SIGILL caught handler=0x3f8c2682be0 mask=0<> 
>> code=ILL_BTCFI addr=0x3f87e823d20 trapno=21
>>
>> if it has that ILL_BTCFI then that is the cause.
>
> With the same blender crash I get the gbd backtrace I posted in my first
> message, with ktrace I get no output at all.  Are the debugging symbols
> included in debug-blender package also useful for ktrace?
>
>>
>>>> May I ask you to try this guess?
>>>
>>> I got the gdb backtrace using the debug-blender package.  I'll download
>>> the ports, compile blender and tell you if your diff helps.
>>
>> it is very likely to help.
>
> --
> Walter