> On 21 Sep 2017, at 12:19, Dave Martin <Dave.Martin@xxxxxxx> wrote: > > On Wed, Sep 20, 2017 at 06:08:21PM +0000, Alan Hayward wrote: >> >>> On 20 Sep 2017, at 12:09, Dave Martin <dave.martin@xxxxxxxxxxxx> wrote: > > [...] > >>>> Given, sve_set_vector_length is called when setting the vector length in >>>> PTRACE_SETREGSET, it looks to me like if you set VL to a value that’s not >>>> supported by the hardware, then it’s going to round down to the previous value. >>>> Is that correct? I’m not sure if that’s explained in the docs? >>> >>> Does this cover it? >>> >>> "On success, the calling thread's vector length is changed to the >>> largest value supported by the system that is less than or equal to vl." >>> >>> (For ptrace, I just cross-reference the PR_SVE_SET_VL behaviour, above.) >> >> For ptrace is it worth mentioning user should do a GET after a SET to confirm >> what VL value was actually set? > > This seems worth a clarification -- I'd thought this was already > mentioned, but it isn't. > > How about: > > The caller must make a further GETREGSET call if it needs to know what VL is > actually set by SETREGSET, unless is it known in advance that the requested > VL is supported. > Looks good to me. Alan.
