Re: [PATCH 2/3] x86: Pass in pt_regs pointer for syscalls that need it

[H. Peter Anvin]

Brian Gerst wrote:
> IMHO, copying the 4th-6th args to a new stack frame is the only way to
> guarantee that gcc won't trash any part of pt_regs.  The question is
> whether to do it unconditionally, or try to be clever and only copy
> them for the syscalls that actually need them.

My guess is that the conditionalization would actually cost more than 
doing it unconditionally.  We're talking a small fraction of a cache 
line, and a set of stores to RAM, which can be buffered.

It's in many ways easier than reorganizing the struct pt_regs.  I'm just 
hypersensitive to adding system call overhead in any way.

	-hpa

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