> 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. The following is the llvm diff: > > https://github.com/llvm/llvm-project/pull/81546 Thank you. I believe Will will be sending a patch to binutils to change the pseudo-C syntax for the instruction to callx instead of callr. We will then adapt GCC accordingly, and both compilers will be doing exactly the same regarding callx. >> >> 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. > >> >> Dave >> -- Bpf mailing list Bpf@xxxxxxxx https://www.ietf.org/mailman/listinfo/bpf
