Is there an `x86` instruction to tell which core the instruction is being run on?

Question

When I cat /proc/cpuinfo, I see 8 cores, with ID\'s from 0 to 7.

Is there an x86 instruction that will report th

Answer 1

Except already described CPUID and RDTSCP instructions also there is new one RDPID instruction (Intel SDM download page) exactly for this purpose.

Description

Reads the value of the IA32_TSC_AUX MSR (address C0000103H) into the destination register. The value of CS.D and operand-size prefixes (66H and REX.W) do not affect the behavior of the RDPID instruction.

Notes:

RDPID reads processor core id as uint32_r or uint64_r, so read value will not in sequential range [0,MAX_CPU_COUNT]

RDPID is new instruction so it is not widely supported by hardware