General purpose means all of these registers might be used with any instructions doing computation with general purpose registers while, for example, you cannot do whatever you want with the instruction pointer (RIP) or the flags register (RFLAGS).
Some of these registers were envisioned to be used for specific use, and commonly are. The most critical ones are the RSP and RBP.
Should you need to use them for your own purpose, you should save their contents before storing something else inside, and restore them to their original value when done.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…