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Re: [PATCH V2 2/8] bpf: new GCC port
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
x4: call x2
x2: call x1
x1: do things once here
to do fixed number of iteration loops. Disgusting? You decide :-)
(Or is something in that not allowed by the verifier?)