On Wed, 9 Oct 2024 18:25:25 +0200 Ard Biesheuvel <[email protected]> wrote:
> > Say we have code of: > > > > pushq r10 > > pushq r11 > > call foo > > popq r11 > > popq r10 > > > > Where we add a kprobe to the start of foo, the callback should be able to > > see what r10 and r11 were. > > Why exactly is that? The contents of R10 and R11 have no purpose going > forward, so is it just to see what some previous code may have left in > them? Because the probe is on the call. Unless they were used between the push and the call, they still have the value you may be looking for. > > > But the restore part is for the function foo to > > see. It shouldn't care about r10 or r11 and if a kprobe updates them, it > > should not have any effect. > > > > What does restoring r10 and r11 give us? > > > > Nothing. Which is why I don't understand why you would need to record > them in the first place. As I mentioned above. Unless they are used after they are pushed, you still have access to them on the call (or the kprobe attached to ftrace). -- Steve
