On Tue, 2017-06-20 at 11:05 +0200, Richard Weinberger wrote: > [adding x86 folks] > > Am 20.06.2017 um 10:49 schrieb Thomas Meyer: > > > > In UML the first userspace ptrace always fails, so init get's killed. > > > > The check "count < fpu_user_xstate_size" was introduced by commit: > > > > commit 91c3dba7dbc199191272f4a9863f86ea3bfd679f > > Author: Yu-cheng Yu <yu-cheng...@intel.com> > > Date: Fri Jun 17 13:07:17 2016 -0700 > > > > x86/fpu/xstate: Fix PTRACE frames for XSAVES > > > > XSAVES uses compacted format and is a kernel instruction. The kernel > > should use standard-format, non-supervisor state data for PTRACE. > > > > 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. Yu-cheng
