> Am 20.06.2017 um 21:53 schrieb Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>: > >> 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 Hi, Is there a user space API to get this value? > > GDB has a fixed X86_XSTATE_MAX_SIZE of 2688. That can become an issue. > > Yu-cheng > >
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