Re: [PATCH v6 bpf-next 12/17] bpf, docs: do not state that indirect jumps are not supported

[Anton Protopopov <a.s.protopopov@gmail.com>]

On 25/10/21 12:15PM, Eduard Zingerman wrote:
> On Sun, 2025-10-19 at 20:21 +0000, Anton Protopopov wrote:
> > The linux-notes.rst states that indirect jump instruction "is not
> > currently supported by the verifier". Remove this part as outdated.
> > 
> > Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
> > ---
> >  Documentation/bpf/linux-notes.rst | 8 --------
> >  1 file changed, 8 deletions(-)
> > 
> > diff --git a/Documentation/bpf/linux-notes.rst b/Documentation/bpf/linux-notes.rst
> > index 00d2693de025..64ac146a926f 100644
> > --- a/Documentation/bpf/linux-notes.rst
> > +++ b/Documentation/bpf/linux-notes.rst
> > @@ -12,14 +12,6 @@ Byte swap instructions
> >  
> >  ``BPF_FROM_LE`` and ``BPF_FROM_BE`` exist as aliases for ``BPF_TO_LE`` and ``BPF_TO_BE`` respectively.
> >  
> > -Jump instructions
> > -=================
> > -
> > -``BPF_CALL | BPF_X | BPF_JMP`` (0x8d), where the helper function
> > -integer would be read from a specified register, is not currently supported
> > -by the verifier.  Any programs with this instruction will fail to load
> > -until such support is added.
> > -
> >  Maps
> >  ====
> >  
> 
> Nit: bpf/standardization/instruction-set.rst needs an update,
>      we don't have anything about `JA|X|JMP` in the "Jump instructions"
>      section there.

Ah yes, thanks.

Also, there is a limitation listed in the llvm doc that -O0
can't be used due to absence of indirect jumps. I wonder if
there should be more limitations introduced since the doc
was written. (I've tried, briefly, to compile selftests with -O0,
but this fails for other reasons, and I didn't have time to dig
into this.)