[systemd-devel] Antw: Re: Antw: Re: rdrand generated with march=winchip-c6 in systemd-241

Ulrich Windl Ulrich.Windl at rz.uni-regensburg.de
Mon May 13 07:18:48 UTC 2019

>>> Reindl Harald <h.reindl at thelounge.net> schrieb am 13.05.2019 um 09:14 in
Nachricht <c450003c-9bca-4d92-40bf-f31361adaa85 at thelounge.net>:

> Am 13.05.19 um 09:10 schrieb Ulrich Windl:
>>>>> tedheadster <tedheadster at gmail.com> schrieb am 11.05.2019 um 19:19 in 
> Nachricht
>> <CAP8WD_Y69T_2gk4+gUan4vKozAYtv_djF7cJ=UuiO8j54D6APw at mail.gmail.com>:
>>> On Sat, May 11, 2019 at 12:30 PM Florian Weimer <fw at deneb.enyo.de> wrote:
>>>> Can you capture register contents at the point of the crash?
>>>> Does this reproduce in a chroot?  Maybe you can trace the whole thing
>>>> with a debugger.  Does the crash reproduce if you single-step through
>>>> the whole function?
>>> Florian,
>>>   I figured out the problem, I just haven't written code to fix it.
>>> The documentation I can find is silent about what is returned in %ecx
>>> and %ebx when calling cpuid function 0x00000001 on IDT Winchip-C6 and
>>> Winchip2.
>>> I think %ecx  should properly contain 0x00000000, but it instead puts
>>> the 'auls' characters from cpuid function 0x00000000 (vendor string
>>> 'CentaurHauls') in %ecx:
>>> %ebx = 0x746e6543 = "Cent"
>>> %edx = 0x48727561 = "aurH"
>>> %ecx = 0x736c7561 = "auls"
>>> This sets bit 30 (0x736c7561) 'on', the 'supports rdrand' bit.
>>> So we have to code around the vendor and chip model in this case.
>>> Jeffrey Walton gave some coding examples I might consider
>>> (https://github.com/weidai11/cryptopp/blob/master/cpu.cpp#L380).
>> I didn't see the start of this thread, but is it another attempt to 
> re-implement /proc/cpuinfo's flags?
> can you please stop all that trolling?

Actually the number of unfriendly words from your side beat mine by an order of magnitude...

> cpuid has *nothing* to do with /proc/cpuinfo
> https://en.wikipedia.org/wiki/CPUID 
> The CPUID instruction (identified by a CPUID opcode) is a processor
> supplementary instruction

Isn't it about to check a CPU's feature depending on the CPU model?


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