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

Ulrich Windl Ulrich.Windl at rz.uni-regensburg.de
Tue May 14 06:03:49 UTC 2019

>>> Lennart Poettering <lennart at poettering.net> schrieb am 13.05.2019 um 09:45
Nachricht <20190513074503.GB9036 at gardel-login>:
> On Mo, 13.05.19 09:18, Ulrich Windl (Ulrich.Windl at rz.uni‑regensburg.de)
> Please guys, stop it.
>> > 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?
> Ulrich, please understand that __get_cpuid() (which the discussion
> here is about) is a gcc and llvm/clang feature weare are just making
> use of. It used by various Linux software, and apparently doesn't work
> entirely correctly on all CPUs in some corner case. The discussion is
> about fixing gcc accordingly, and making it work, so that systemd all
> all other software can work correctly.
> If you think that gcc/llvm are bad for "reimplementing /proc/cpuinfo"
> then please bring that up with those communities, but please stop
> these fruitless discussions here.

The point I was trying to make was: "CPUID" and the model-specific registers
(thus the name) depend very much on the CPU being used. While the kernel makes
grat efforts to get things right, I wondered whether it's the best idea whether
to repeat that effort in an application program.


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