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PUSHF

Pushes the RFLAGS register onto the stack. The RSP register is decremented by 4 or 8 bytes, depending on the operating mode, and the flags are stored at the new stack pointer location.

The following table covers what the source and destinations can be:

DO NOT support LOCK

In 64-bit mode, PUSHF is not supported; PUSHF is available only in compatibility mode. In 64-bit mode, PUSHFQ MUST be used to push the RFLAGS register.

When operating in compatibility mode, the instruction pushes a dword. If the processor is executing in 32-bit mode, it also pushes a dword. Failure to use the correct stack alignment or instruction variant in 64-bit mode will result in an invalid opcode exception.