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SubjectRe: [RFC 1/2] x86/entry/64: Use the TSS sp2 slot for rsp_scratch
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On 07/22/2018 10:45 AM, Andy Lutomirski wrote:
> + /*
> + * sp2 is scratch space used by the SYSCALL64 handler. Linux does
> + * not use rung 2, so sp2 is not otherwise needed.
> + */
> u64 sp2;

Could we call out the actual thing that we use this slot for, and the
symbol name so folks can find the corresponding code that does this?
While I know the spot in entry_64 you're talking about, it might not be
patently obvious to everyone, and it's also a bit more challenging to
grep for than normal C code.

Maybe:

/*
* Since Linux does not use ring 2, the 'sp2' slot is unused.
* entry_SYSCALL_64 uses this as scratch space to stash the user
* %RSP value.
*/

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