On Fri, Oct 13, 2017 at 5:53 AM, Adrian Szyndela via iovisor-dev <iovisor-dev@lists.iovisor.org> wrote: > > W dniu 04.10.2017 o 21:14, Y Song pisze: >> >> On Wed, Oct 4, 2017 at 3:24 AM, Adrian Szyndela via iovisor-dev >> <iovisor-dev@lists.iovisor.org> wrote: >>> >>> - return type of bpf_pseudo_fd is 'u64', and it is passed to functions >>> that >>> take pointers; the compiler generates 'trunc' in IR for this, which >>> becomes >>> shift-left + shift-right in final bpf code; and bpf verifier does not >>> like >>> it when pointers are shifted. We worked it around by changing return type >>> of >>> bpf_pseudo_fd/llvm.bpf.pseudo from 'u64' to 'void *' - both in bcc >>> >>> (https://github.com/aszyndela/bcc/commit/8eb8fb2e265b93d38c1ad53efcb7da8883a3d643) >>> and llvm >>> (include/llvm/IR/IntrinsicsBPF.td): >>> >>> def int_bpf_pseudo : GCCBuiltin<"__builtin_bpf_pseudo">, >>> - Intrinsic<[llvm_i64_ty], [llvm_i64_ty, llvm_i64_ty]>; >>> + Intrinsic<[llvm_ptr_ty], [llvm_i64_ty, llvm_i64_ty]>; >>> >>> Obviously we don't know what we're doing, but at least it works for us. >> >> >> This should work as well. essentially bpf_pseudo tries to convert a >> load map_id to load_imm64 address. So its return value is indeed a ptr. > > > I asked about it on llvm-dev and the only suggestion I got so far is to set > bpf target for clang: > https://lists.llvm.org/pipermail/llvm-dev/2017-October/118149.html > > And it makes sense... > > We can easily get into trouble when we mix two targets in the process. For > example, it looks like sizeofs are computed at the "clang" stage, but actual > sizes of some types are "known" at the "llc" stage. > > However, switching to bpf target for the whole process takes away > convenience and maintainability: we can't rely on including kernel headers > anymore. So we have to craft everything we need by hand, including struct > pt_regs... > > Any thoughts how to handle this?
All these are valid. For certain program types e.g., networking where pt_regs are not needed, you can already use -target bpf in clang. Check linux:tools/testing/selftests/bpf/Makefile. Since currently we do not have good solutions for pt_regs when "clang -target bpf" is used, let us stick to the approach "clang -target arm"/"llc -target bpf". > _______________________________________________ > iovisor-dev mailing list > iovisor-dev@lists.iovisor.org > https://lists.iovisor.org/mailman/listinfo/iovisor-dev _______________________________________________ iovisor-dev mailing list iovisor-dev@lists.iovisor.org https://lists.iovisor.org/mailman/listinfo/iovisor-dev
