Date: Thu, 16 Apr 2020 11:21:56 -0400 From: Jeffrey Walton <noloader@...il.com> To: musl@...ts.openwall.com Cc: libc-alpha@...rceware.org, libc-dev@...ts.llvm.org, linuxppc-dev@...ts.ozlabs.org Subject: Re: Powerpc Linux 'scv' system call ABI proposal take 2 On Wed, Apr 15, 2020 at 8:17 PM Nicholas Piggin <npiggin@...il.com> wrote: > > Excerpts from Rich Felker's message of April 16, 2020 8:55 am: > > On Thu, Apr 16, 2020 at 07:45:09AM +1000, Nicholas Piggin wrote: > >> I would like to enable Linux support for the powerpc 'scv' instruction, > >> as a faster system call instruction. > >> > >> This requires two things to be defined: Firstly a way to advertise to > >> userspace that kernel supports scv, and a way to allocate and advertise > >> support for individual scv vectors. Secondly, a calling convention ABI > >> for this new instruction. > >> ... > > Note that any libc that actually makes use of the new functionality is > > not going to be able to make clobbers conditional on support for it; > > branching around different clobbers is going to defeat any gains vs > > always just treating anything clobbered by either method as clobbered. > > Well it would have to test HWCAP and patch in or branch to two > completely different sequences including register save/restores yes. > You could have the same asm and matching clobbers to put the sequence > inline and then you could patch the one sc/scv instruction I suppose. Could GCC function multiversioning work here? https://gcc.gnu.org/wiki/FunctionMultiVersioning It seems like selecting a runtime version of a function is the sort of thing you are trying to do. Jeff
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.