On Fri, Apr 26, 2024 at 01:18:28PM -0700, Dave Thaler wrote: > This patch elaborates on the use of PC by expanding the PC acronym, > explaining the units, and the relative position to which the offset > applies. > > v1->v2: reword per feedback from Alexei > > Signed-off-by: Dave Thaler <dthaler1968@xxxxxxxxxxxxxx> > --- > Documentation/bpf/standardization/instruction-set.rst | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/Documentation/bpf/standardization/instruction-set.rst b/Documentation/bpf/standardization/instruction-set.rst > index b44bdacd0..766f57636 100644 > --- a/Documentation/bpf/standardization/instruction-set.rst > +++ b/Documentation/bpf/standardization/instruction-set.rst > @@ -469,6 +469,12 @@ JSLT 0xc any PC += offset if dst < src signed > JSLE 0xd any PC += offset if dst <= src signed > ======== ===== ======= ================================= =================================================== > > +where 'PC' denotes the program counter, and the offset to increment by > +is in units of 64-bit instructions relative to the instruction following > +the jump instruction. Thus 'PC += 1' skips execution of the next > +instruction if it's a basic instruction and fails verification if the > +next instruction is a 128-bit wide instruction. Should we say "results in undefined behavior" rather than "fails verification"? I'm not sure if we should be dictating verifier semantics in the ISA document. > + > The BPF program needs to store the return value into register R0 before doing an > ``EXIT``. > > -- > 2.40.1 > > -- > Bpf mailing list > Bpf@xxxxxxxx > https://www.ietf.org/mailman/listinfo/bpf
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