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
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
