> We do not support any load/sotre instruction with mode BPF_MSH in > binutils. Should we do so? What are these? > >> Under "Load and store instructions", various mode modifiers are documented. >> I notice that BPF_MSH (0xa0) is not documented, but appears to be in use in >> various projects, including Linux, BSD, seccomp, etc. and is even documented >> in various books such as >> https://www.google.com/books/edition/Programming_Linux_Hacker_Tools_Uncovere >> d/yqHVAwAAQBAJ?hl=en&gbpv=1&dq=%22BPF_MSH%22&pg=PA129&printsec=frontcover >> >> Should we document it as deprecated and add it to the set of deprecated >> instructions (the legacy conformance group) like BPF_ABS and BPF_IND >> already are? >> >> Also, for purposes of the IANA registry of instructions where we list which >> opcodes are "(deprecated, implementation-specific)", I currently list all >> possible BPF_ABS and BPF_IND opcodes regardless of whether they were >> ever used (I didn't check which were used and which might not have been), >> so I could just list all possible BPF_MSH opcodes similarly. But if we know >> that some were never used then I don't need to do so, so I guess I should >> ask: >> do we have a list of which combinations were actually used or should we >> continue to just deprecate all combinations? >> >> As an example, >> https://github.com/seccomp/libseccomp/blob/main/tools/scmp_bpf_disasm.c#L68 >> lists 6 variants of BPF_MSH: LD and LDX, for B, H, and W (but not DW). >> Other sources like the book page referenced above, and the BSD man page, >> list only BPF_LDX | BPF_B | BPF_MSH, which is in Linux sources such as >> https://elixir.bootlin.com/linux/v6.8-rc1/source/lib/test_bpf.c#L368 >> >> So, should we list the DW variants as deprecated, or never assigned? >> Should we list the H, W, and LD variants as deprecated, or never assigned? >> >> What about DW and LDX variants of BPF_IND and BPF_ABS? 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}, >> Dave -- Bpf mailing list Bpf@xxxxxxxx https://www.ietf.org/mailman/listinfo/bpf
