RDRAND instruction set extension

RDRAND returns a 16-, 32- or 64-bit random number from a deterministic random bit generator in the processor (built to NIST SP 800-90A), which an on-chip entropy source reseeds frequently. It sets CF when the value is valid. When many cores ask at once, or when the generator’s self-test rejects a value, CF is clear and the destination zero; Intel recommends retrying a limited number of times, such as ten, rather than looping forever.

For seeding a generator of one’s own, RDSEED gives access to the entropy source itself. RDRAND came with Intel’s Ivy Bridge and AMD’s Excavator.

Instructions

Mnemonics with at least one form in RDRAND. Each page lists all forms of the mnemonic, including those of other extensions.

Mnemonic	Summary	Forms
RDRAND	Returns a random number from the processor's hardware generator; CF=1 means the value is valid, CF=0 that none was ready.	1

CPUID and processors

XED splits RDRAND into 1 ISA set. Software can use a form when the processor reports every CPUID bit of one alternative of the form's ISA set.

XED ISA sets of RDRAND. Alternatives are separated by “or”; processors follow XED’s chip model, which covers AMD processors up to Zen 2.

ISA set	CPUID	Processors in XED
`RDRAND` RDRAND	RDRAND `CPUID.01H:ECX[30]` RDRAND	Ivy Bridge, Haswell, Broadwell, Skylake, Comet Lake, Cannon Lake, Ice Lake (client), Tiger Lake, Alder Lake, Arrow Lake, Panther Lake, Nova Lake, Skylake-SP, Cascade Lake, Cooper Lake, Ice Lake (server), Sapphire Rapids, Emerald Rapids, Granite Rapids, Diamond Rapids, Silvermont, Goldmont, Goldmont Plus, Tremont, Snow Ridge, Lakefield, Sierra Forest, Clearwater Forest, Knights Landing, Knights Mill, Zen, Zen+, Zen 2

Instructions

CPUID and processors

Sources