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

Reindl Harald h.reindl at thelounge.net
Mon May 13 07:14:50 UTC 2019

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?
cpuid has *nothing* to do with /proc/cpuinfo

The CPUID instruction (identified by a CPUID opcode) is a processor
supplementary instruction

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