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? > > Dave
