Re: um: PTRACE_SETREGSET failure with XSTATE on Kabylake CPU

[Richard Weinberger]

Yu-cheng,

Am 20.06.2017 um 20:04 schrieb Yu-cheng Yu:
>>> So to summarize:
>>>
>>> - PTRACE_GETREGSET with NT_X86_XSTATE gets 832 and return 832, with no
>>> error.
>>>
>>> - PTRACE_SETREGSET get 832 (sizeof struct _xstate) but wants at least
>>> 1088, otherwise it will fail with -EFAULT (why not -EINVAL?)
>>>
>>> Ideas?
> 
> We considered allowing a partial XSAVE buffer for PTRACE_SETREGSET, but
> it was that the XSAVE instruction requires a full-size buffer led to
> this choice.  Using a smaller buffer for XSAVE causes a fault.

So, this code is not supposed to work?

iov.iov_base = fp_regs;
iov.iov_len = sizeof(struct _xstate);
ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov);
ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov);

This is what UML does and on Thomas's new Laptop PTRACE_SETREGSET is failing.

Thanks,
//richard