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 -- To unsubscribe from this list: send the line "unsubscribe linux-x86_64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
