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PUSHFD

Pushes the current value of the EFLAGS register onto the stack and decrements the stack pointer.

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

DO NOT support LOCK

In x86-64 architecture, PUSHFD is only supported in compatibility mode. In 64-bit mode, this instruction is invalid; PUSHFQ SHALL be used instead to push the RFLAGS register.

When executing PUSHFD, the stack pointer (ESP) is decremented by 4 bytes. If the stack is aligned to a specific boundary, this operation will change that alignment. Users MUST ensure that the stack is properly aligned before calling functions after a PUSHFD operation to avoid performance degradation or crashes on certain ABIs.