NASM 2.05 based x86 Instruction Reference[ch356]

A.5.330 WRSHR: Write SMM Header Pointer Register WRSHR r/m32 ; 0F 37 /0 [386,CYRIX,SMM] WRSHR loads the contents of either a 32-bit memory location or a 32-bit register into the SMM header pointer register. See also RDSHR (section A.5.272).