On Tue, Feb 6, 2024 at 8:42 AM <dthaler1968@xxxxxxxxxxxxxx> wrote: > > Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Tue, Jan 30, 2024 at 11:49 AM Jose E. Marchesi > > <jose.marchesi@xxxxxxxxxx> wrote: > > > > clang generates BPF code with opcode 0x8d (BPF_CALL | BPF_X, which > > > > it calls "callx"), when compiling with -O0 or -O1. Of course -O2 is > > > > recommended, but if anyone later defines opcode 0x8d for anything > > > > other than what clang means by it, it could cause problems. > > > > > > GCC also generates BPF_CALL|BPF_X also named callx, but only if the > > > experimental -mxbpf option is passed to the compiler. > > > > > > I recommend this particular encoding to be specifically reserved for a > > > future `call REG' for when/if a time comes when the BPF verifier > > > supports some form of indirect calls. > > > > +1. > > Same thinking from llvm pov. > > CALL|X is what we will use when the kernel supports indirect calls. > > I think it means we need to add a 'reserved' category to the spec. > > My reading of this thread is that there seems to be consensus that: > 1) CALL|X should have an entry in the IANA registry with its own conformance group, > 2) The intended meaning is understood, > 3) clang and gcc both implement it already with the intended meaning, > 4) The Linux kernel might support it someday. > > I'd propose we make it its own conformance group called "callx", > which of course the Linux kernel does not yet support, but clang and gcc do. > > Rationale: > * There may be other instructions reserved over time in the future so > using a more specific name than just "reserved" is good since later > additions require new groups with different names. > * Defining it now with the meaning already implemented by clang & gcc > means that no changes are needed later once Linux supports it. > * ebpf-for-windows is likely to start supporting it in the very near future > as a result of this thread. There is already a github pull request under > review to add support for it in the PREVAIL verifier. All makes sense to me. Could you share a prevail pull link? I'm curious what it means to support it in that verifier? -- Bpf mailing list Bpf@xxxxxxxx https://www.ietf.org/mailman/listinfo/bpf
