> -----Original Message----- > From: Yonghong Song <yonghong.song@xxxxxxxxx> > Sent: Monday, February 12, 2024 2:49 PM > To: dthaler1968@xxxxxxxxxxxxxx; 'Jose E. Marchesi' > <jose.marchesi@xxxxxxxxxx>; 'Dave Thaler' > <dthaler1968=40googlemail.com@xxxxxxxxxxxxxx> > Cc: bpf@xxxxxxxxxxxxxxx; bpf@xxxxxxxx > Subject: Re: [Bpf] [PATCH bpf-next v2] bpf, docs: Add callx instructions in new > conformance group > > > On 2/12/24 1:52 PM, dthaler1968@xxxxxxxxxxxxxx wrote: > >> -----Original Message----- > >> From: Yonghong Song <yonghong.song@xxxxxxxxx> > >> Sent: Monday, February 12, 2024 1:49 PM > >> To: Jose E. Marchesi <jose.marchesi@xxxxxxxxxx>; Dave Thaler > >> <dthaler1968=40googlemail.com@xxxxxxxxxxxxxx> > >> Cc: bpf@xxxxxxxxxxxxxxx; bpf@xxxxxxxx; Dave Thaler > >> <dthaler1968@xxxxxxxxx> > >> Subject: Re: [Bpf] [PATCH bpf-next v2] bpf, docs: Add callx > >> instructions in new conformance group > >> > >> > >> On 2/12/24 1:28 PM, Jose E. Marchesi wrote: > >>>> +BPF_CALL 0x8 0x1 call PC += reg_val(imm) BPF_JMP | BPF_X > >> only, see `Program-local functions`_ > >>> If the instruction requires a register operand, why not using one of > >>> the register fields? Is there any reason for not doing that? > >> Talked to Alexei and we think using dst_reg for the register for > >> callx insn is better. I will craft a llvm patch for this today. Thanks! > > Why dst_reg instead of src_reg? > > BPF_X is supposed to mean use src_reg. > > Let us use dst_reg. Currently, for BPF_K, we have src_reg for a bunch of flags > (pseudo call, kfunc call, etc.). So for BPF_X, let us preserve this property as > well in case in the future we will introduce variants for callx. Ah yes, that makes sense. > The following is the llvm diff: > > https://github.com/llvm/llvm-project/pull/81546 Which llvm release is it targeted for? 18.1.0-rc3? 18.1.1? later? > > But this thread is about reserving/documenting the existing practice, > > since anyone trying to use it would run into interop issues because > > of existing clang. Should we document both and list one as deprecated? > > I think just documenting the new encoding is good enough. But other > people can chime in just in case that I missed something. Ok. Dave -- Bpf mailing list Bpf@xxxxxxxx https://www.ietf.org/mailman/listinfo/bpf
