Supporting 64-bit ARM systems [LWN.net]

Supporting 64-bit ARM systems

Posted Jul 17, 2012 21:58 UTC (Tue) by Tuna-Fish (subscriber, #61751)
In reply to: Supporting 64-bit ARM systems by jzbiciak
Parent article: Supporting 64-bit ARM systems

ARMv8 really is that different. As 64-bit forced break in backcompat, they got rid of everything they felt was not a good idea in a modern instruction set. Gone are the multiple load instructions, simd on gprs and conditions on everything. Instead, we now have a zero reg and 31 gprs, IP and SP(!) not included.

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Supporting 64-bit ARM systems

Posted Jul 17, 2012 22:40 UTC (Tue) by jzbiciak (✭ supporter ✭, #5246) [Link]

I'm not sad to see the IP (aka PC) leave the GPR file. It's a concept that was past its freshness date in the 80s.

But SP's not a GPR? Wow... It makes a certain amount of sense, really, since stack pointers move in rather particular ways. Treating it specially may help when speculating memory accesses. I'm going to guess they have dedicated ways of generating SP-relative addresses for local variables, along with frame pointers.

Otherwise, it sounds very MIPS-y, at least superficially.