rdrand generated with march=winchip-c6 in systemd-241

[Segher Boessenkool]

On Tue, May 07, 2019 at 08:50:07AM -0400, tedheadster wrote:
>   I compiled systemd-241 and expressly set march=winchip-c6 (an i486
> class cpu). It generated illegal instructions (rdrand) in the code.

But it should not execute it, it is guarded by some cpuid things.

If the assembler does not like the insn, first do (in the same asm) an
assembler pseudo-instruction to select a CPU that does have that insn,
then the rdrand, and then the original CPU again.  Or write the bytes
of the instruction encoding directly.


Segher