From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Richard Weinberger <richard@nod.at>
Cc: Thomas Meyer <thomas@m3y3r.de>,
elicooper@gmx.com, linux-kernel@vger.kernel.org,
"open list:USER-MODE LINUX (UML)"
<user-mode-linux-devel@lists.sourceforge.net>,
linux-x86_64@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
Ingo Molnar <mingo@redhat.com>
Subject: Re: um: PTRACE_SETREGSET failure with XSTATE on Kabylake CPU
Date: Tue, 20 Jun 2017 12:53:18 -0700 [thread overview]
Message-ID: <1497988398.22550.5.camel@test-lenovo> (raw)
In-Reply-To: <2fc7383c-852a-be3c-f934-b125fe9bdba2@nod.at>
On Tue, 2017-06-20 at 20:59 +0200, Richard Weinberger wrote:
> Yu-cheng,
>
> Am 20.06.2017 um 20:17 schrieb 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.
>
> Hmm, I think we need to do what gdb does, it uses a buffer of size X86_XSTATE_MAX_SIZE.
>
Linux kernel determines XSAVE buffer size from CPUID:
http://elixir.free-electrons.com/linux/latest/source/arch/x86/kernel/fpu/xstate.c#L626
GDB has a fixed X86_XSTATE_MAX_SIZE of 2688. That can become an issue.
Yu-cheng
next prev parent reply other threads:[~2017-06-20 19:55 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-20 1:56 um: PTRACE_SETREGSET failure with XSTATE on Kabylake CPU Thomas Meyer
2017-06-20 6:58 ` Richard Weinberger
2017-06-20 8:49 ` Thomas Meyer
2017-06-20 9:05 ` Richard Weinberger
2017-06-20 18:04 ` Yu-cheng Yu
2017-06-20 18:17 ` Richard Weinberger
2017-06-20 18:59 ` Richard Weinberger
2017-06-20 19:53 ` Yu-cheng Yu [this message]
2017-06-20 20:13 ` Thomas Meyer
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