> On Mon, Jan 8, 2024 at 8:00 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: >> >> On Fri, Jan 05, 2024 at 04:07:11PM -0600, David Vernet wrote: >> > >> > So how do we want to move forward here? It sounds like we're leaning >> > toward's Alexei's proposal of having: >> > >> > - Base Integer Instruction Set, 32-bit >> > - Base Integer Instruction Set, 64-bit >> > - Integer Multiplication and Division >> > - Atomic Instructions >> >> As in the 64-bit integer set would be an add-on to the first one which >> is the core set? In that case that's fine with me, but the above >> wording is a bit suboptimal. > > yes. > Here is how I was thinking about the grouping: > 32-bit set: all 32-bit instructions those with BPF_ALU and BPF_JMP32 > and load/store. > > 64-bit set: above plus BPF_ALU64 and BPF_JMP. > > The idea is to allow for clean 32-bit HW offloads. > We can introduce a compiler flag that will only use such instructions > and will error when 64-bit math is needed. > Details need to be thought through, of course. > Right now I'm not sure whether we need to reduce sizeof(void*) to 4 > in such a case or normal 8 will still work, but from ISA perspective > everything is ready. 32-bit subregisters fit well. > The compiler work plus additional verifier smartness is needed, > but the end result should be very nice. > Offload of bpf programs into 32-bit embedded devices will be possible. This is very interesting. Sounds like, on one hand, introducing ilp32 and lp64 C data models for BPF: ilp32 int, long, pointers -> 32 bit short -> 16 bit char -> 8 bit lp64 long, pointers -> 64 bit int -> 32 bit short -> 16 bit char -> 8 bit On the other hand, compiler flags -m32 and -m64 could determine what instruction groups are generated and what C data model is used: -m32 Use ilp32 data model for C. Use 32-bit instruction set. -m64 Use lp64 data model for C. Use both 32-bit (if/when alu32) and 64-bit instruction sets. And perhaps introducing a bit in the ELF flags section identifying a 32-bit binary. Something like EF_BPF_32. Would 64-bit ELF be used also in cases where BPF is offloaded to 32-bit devices? >> > And then either having 3 separate groups for the calls, or putting all 3 >> > in the basic group? I'd lean towards the latter given that we're >> > decoupling ISA compliance from the verifier, but don't feel strongly >> > either way. >> >> What would be the three different groups for the calls? I think just >> having the call instruction in the base group should be fine. We'll >> need to put in some wording that having support for any kind of call >> depends on the program type. > > +1 -- Bpf mailing list Bpf@xxxxxxxx https://www.ietf.org/mailman/listinfo/bpf
