NASM 2.05 based x86 Instruction Reference[ch289]
A.5.265 PUSHFx: Push Flags Register PUSHF ; 9C [8086] PUSHFD ; o32 9C [386] PUSHFW ; o16 9C [8086] - PUSHFW pushes the bottom 16 bits of the flags register (or the whole flags register, on processors below a 386) onto the stack. - PUSHFD pushes the entire flags register onto the stack. PUSHF is an alias mnemonic for either PUSHFW or PUSHFD, depending on the current BITS setting. See also POPF (section A.5.246).