Re: [PATCH v2 14/28] arm64/sve: Backend logic for setting the vector length
Dave Martin <[email protected]>
| Newsgroups | gmane.linux.kernel.cross-arch,gmane.comp.lib.glibc.alpha,gmane.comp.gdb.devel,gmane.comp.emulators.kvm.arm.devel,gmane.linux.ports.arm.kernel |
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| Message-ID | <[email protected]> |
On Wed, Sep 20, 2017 at 06:08:21PM +0000, Alan Hayward wrote: > > > On 20 Sep 2017, at 12:09, Dave Martin <[email protected]> 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. [...] Cheers ---Dave