JMPABS instruction (APX)

Before APX, a jump to an arbitrary 64-bit address needed the target in a register or in memory, which makes it an indirect branch. JMPABS carries the target as a 64-bit immediate, so it is a direct jump that can reach anywhere in the address space. The encoding is the REX2 prefix with M0=0 and W=0, the opcode A1 and the eight-byte target: 11 bytes in all.

A non-canonical target raises #GP. The 66, 67, F0, F2 and F3 prefixes make it raise #UD, and segment overrides are ignored. Performance monitoring and last branch records treat it like any direct jump, but unlike other direct jumps, Intel Processor Trace reports its target with a TIP packet.

Forms

Every encoding of JMPABS that Intel XED knows, one row per XED instruction form (iform). How to read the notation.

Instruction	Encoding	Requires
`JMPABS imm64` JMPABS_ABSBRu64_APX	`REX2.W0 A1 io`	APX_F

Operation

What the forms do, in pseudocode that our tests run against results recorded on real processors. How to read.

t = target.read()                # the 64-bit address, as encoded
if not canonical(t):
    fault(GP, 0)
rip = t

Not run on a processor: none of these processors has APX.

Operands

What each form reads and writes, as Intel XED records it: the operands of its syntax, in order, and the implicit ones that the syntax does not name. How to read.

Operand	Kind	Action
`JMPABS imm64`
`imm64`	explicit	read
`RIP`	implicit	write

Flags

None: XED records no flag that the forms test or change.

Exceptions

The exception class is XED's name for the set of exception conditions that a form follows. How to read.

All forms: APX-LEGACY-JMPABS

CPUID and processors

Each form belongs to an XED ISA set. A form can be used when the processor reports every CPUID bit of one of its ISA set's alternatives.

CPUID requirements and processors of the XED ISA sets above. Alternatives are separated by “or”; processors follow XED’s chip model, whose AMD processors end with Zen 2, and the CPU data of this site for Zen 3 to Zen 6.

ISA set	CPUID	Processors
`APX_F` APX	APX_F `CPUID.(EAX=07H,ECX=1):EDX[21]` APX_F	Nova Lake, Diamond Rapids

More APX instructions

All 88 APX instructions