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

[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?

> 
> - Matthew
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