On Wed, May 25, 2016 at 12:30:17PM -0700, David Miller wrote: > From: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx> > Date: Tue, 24 May 2016 03:04:30 +0300 > > > +To clear that top halves, automatic wrappers are introduced. They clear all > > +required registers before passing control to regular syscall handler. > > Why have one of these for every single compat system call, rather than > simply clearing the top half of all of these registers unconditionally > in the 32-bit system call trap before the system call is invoked? > > That's what we do on sparc64. > > And with that, you only need wrappers for the case where there needs > to be proper sign extention of a 32-bit signed argument. It was discussed as one of possible solutions. The downside of it is that we cannot pass 64-bit types (like off_t) in single register. The other downside is that we clear top halves for every single syscall, and it looks excessive. So, from spark64 and s390 approaches we choosed second. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
