On Mon, May 10, 2021 at 03:01:48PM -0700, Kees Cook wrote: > On Mon, May 10, 2021 at 02:45:03PM +0100, Mark Rutland wrote: [...] > > That's 441301 new MOVs, and the equivalent of 442511 new instructions > > overall. There are 135728 new MOVs to x16 and x17 specifically, which > > account for ~31% of that. > > I assume the x16/x17 case could be addressed by the compiler if it > examined the need for PLTs, or is that too late (in the sense that the > linker is doing that phase)? Most (all?) PLTs will be created at link time, and IIUC the compiler simply has to assume any non-static function might have a PLT, since the AAPCS permits that. Maybe some of the smaller memory size models don't permit PLTs, but I have no real knowledge of that area and I'm already out on a limb. LTO could probably help with visiblity, but otherwise I don't see a way the compiler could be sure a PLT won't exist. > Regardless, I will update the documentation on this feature. :) Great; thanks! Mark.
