On Tue, Aug 20, 2019 at 11:14:35PM +0200, Jose E. Marchesi wrote:
> The kernel verifier doesn't allow backward jumps.
>
> This may change at some point. There is much discussion among the
> kernel hackers in whether it is possible to allow bounded loops in a
> safe way. In that case, some of the restrictions may be lifted.
>
> For now, only loops that can be peeled/massaged and then fully unrolled
> are supported.
You can also generate code like
x5: call x4
jump x1
x4: call x2
x2: call x1
x1: do things once here
ret
to do fixed number of iteration loops. Disgusting? You decide :-)
(Or is something in that not allowed by the verifier?)
Segher
