x86-64.net

Instruction

WRUSSD

Lets ring-0 code write a 32-bit value to a user-mode shadow stack.

Extensions
Forms
2 (1 Legacy, 1 EVEX)
Data
Intel XED v2026.08.23

Forms

Every encoding of WRUSSD that Intel XED knows, one row per XED instruction form (iform). How to read the notation.
InstructionEncodingRequires
WRUSSD m32, r32 WRUSSD_MEMu32_GPR32u3266 0F 38 F5 /rCET
WRUSSD m32, r32 WRUSSD_MEMu32_GPR32u32_APXEVEX.LLZ.66.MAP4.W0 65 /rAPX_F + CET

Intrinsics

The C intrinsics of Clang 23.1.2 that compile to WRUSSD, each with the form it compiles to and the Clang options it needs. The forms come from compiling every intrinsic and decoding the result with Intel XED; all intrinsics A–Z explains the method.

IntrinsicCompiles to
_wrussd void _wrussd(unsigned int __a, void *__p)

WRUSSD m32, r32 Legacy -mshstk

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, which covers AMD processors up to Zen 2.
ISA setCPUIDProcessors in XED
CET

CET
CPUID.(EAX=07H,ECX=0):ECX[7] CET

Tiger Lake, Alder Lake, Arrow Lake, Panther Lake, Nova Lake, Sapphire Rapids, Emerald Rapids, Granite Rapids, Diamond Rapids, Sierra Forest, Clearwater Forest
APX_F_CET

APX_F + CET
CPUID.(EAX=07H,ECX=1):EDX[21] APX_F
CPUID.(EAX=07H,ECX=0):ECX[7] CET

Nova Lake, Diamond Rapids

More APX instructions

All 88 APX instructions

Sources

  1. Intel XED v2026.08.23 (commit 0bcb6237345c): forms, encodings, ISA sets, CPUID bits and chip model.
  2. Clang's x86 intrinsic headers, LLVM 23.1.2 (commit 85ac56026243): the intrinsics, their signatures and doc comments, and the Clang of that release, which compiled each of them.
  3. Intel Advanced Performance Extensions (Intel APX) Architecture Specification, revision 7.0 (July 2025)

The tables are derived from Intel XED, Copyright Intel Corporation, licensed under the Apache License 2.0; x86-64.net converted and reformatted them. The intrinsics and their signatures come from Clang, part of the LLVM Project, licensed under the Apache License 2.0 with LLVM Exceptions. The text is our own.