CMPXCHG8B
SEMAPHORE PENTIUMREAL x86_64
CMPXCHG8B is an instruction of the x86_64 architecture (x86 / x86-64 (covers 16/32/64-bit modes)), category SEMAPHORE. This page lists its 2 encoding forms, distinguished by opcode bytes: 0F, C7.
Each form below links to its full decode: the operand roles and where each one is encoded in the instruction, the flag and register effects, and any micro-op sequence authored for it.
X86_CMPXCHG8B_X86_LEGACY_0F_C7_298793
m64,
XED_CMPXCHG8B_X86_LEGACY_0F_C7_485727
MEM0:rcw:q REG0=XED_REG_EDX:rcw:SUPP REG1=XED_REG_EAX:rcw:SUPP REG2=XED_REG_ECX:r:SUPP REG3=XED_REG_EBX:r:SUPP MEM0:rcw:q REG0=XED_REG_EDX:rcw:SUPP REG1=XED_REG_EAX:rcw:SUPP REG2=XED_REG_ECX:r:SUPP REG3=XED_REG_EBX:r:SUPP