RE: [Bpf] ISA: BPF_MSH and deprecated packet access instructions

[dthaler1968@googlemail.com]

I asked:
> >> What about DW and LDX variants of BPF_IND and BPF_ABS?

Jose E. Marchesi <jose.marchesi@oracle.com> wrote:
> These we support:
> 
>   /* Absolute load instructions, designed to be used in socket filters.
*/
>   {BPF_INSN_LDABSB, "ldabsb%W%i32", "r0 = * ( u8 * ) skb [ %i32 ]",
>    BPF_V1, BPF_CODE, BPF_CLASS_LD|BPF_SIZE_B|BPF_MODE_ABS},
>   {BPF_INSN_LDABSH, "ldabsh%W%i32", "r0 = * ( u16 * ) skb [ %i32 ]",
>    BPF_V1, BPF_CODE, BPF_CLASS_LD|BPF_SIZE_H|BPF_MODE_ABS},
>   {BPF_INSN_LDABSW, "ldabsw%W%i32", "r0 = * ( u32 * ) skb [ %i32 ]",
>    BPF_V1, BPF_CODE, BPF_CLASS_LD|BPF_SIZE_W|BPF_MODE_ABS},
>   {BPF_INSN_LDABSDW, "ldabsdw%W%i32", "r0 = * ( u64 * ) skb [ %i32 ]",
>    BPF_V1, BPF_CODE, BPF_CLASS_LD|BPF_SIZE_DW|BPF_MODE_ABS},
> 
>   /* Generic load instructions (to register.)  */
>   {BPF_INSN_LDXB, "ldxb%W%dr , [ %sr %o16 ]", "%dr = * ( u8 * ) ( %sr %o16
)",
>    BPF_V1, BPF_CODE, BPF_CLASS_LDX|BPF_SIZE_B|BPF_MODE_MEM},
>   {BPF_INSN_LDXH, "ldxh%W%dr , [ %sr %o16 ]", "%dr = * ( u16 * ) ( %sr
%o16
> )",
>    BPF_V1, BPF_CODE, BPF_CLASS_LDX|BPF_SIZE_H|BPF_MODE_MEM},
>   {BPF_INSN_LDXW, "ldxw%W%dr , [ %sr %o16 ]", "%dr = * ( u32 * ) ( %sr
%o16
> )",
>    BPF_V1, BPF_CODE, BPF_CLASS_LDX|BPF_SIZE_W|BPF_MODE_MEM},
>   {BPF_INSN_LDXDW, "ldxdw%W%dr , [ %sr %o16 ]","%dr = * ( u64 * ) ( %sr
> %o16 )",
>    BPF_V1, BPF_CODE, BPF_CLASS_LDX|BPF_SIZE_DW|BPF_MODE_MEM},

Yonghong Song <yonghong.song@linux.dev> wrote:
> I don't know how to do proper wording in the standard. But DW and LDX
> variants of BPF_IND/BPF_ABS are not supported by verifier for now and they
> are considered illegal insns.

Although the Linux verifier doesn't support them, the fact that gcc does
support
them tells me that it's probably safest to list the DW and LDX variants as
deprecated as well, which is what the draft already did in the appendix so
that's good (nothing to change there, I think).

Dave