On Fri, Aug 15, 2014 at 12:16 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote: > On Fri, Aug 15, 2014 at 12:02 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >>> >>> correct. eBPF program would be using 8-byte read on 64-bit kernel >>> and 4-byte read on 32-bit kernel. Same with access to ptrace fields >>> and pretty much all other fields in the kernel. The program will be >>> different on different kernels. >>> Say, this bpf_context struct doesn't exist at all. The programs would >>> still need to be different to walk in-kernel data structures... >> >> Hmm. I guess this isn't so bad. >> >> What's the actual difficulty with using u64? ISTM that, if the clang >> front-end can't deal with u64, there's a bigger problem. Or is it >> something else I don't understand. > > clang/llvm has no problem with u64 :) > This bpf_context struct for tracing is trying to answer the question: > 'what's the most convenient way to access tracepoint arguments > from a script'. > When kernel code has something like: > trace_kfree_skb(skb, net_tx_action); > the script needs to be able to access this 'skb' and 'net_tx_action' > values through _single_ data structure. > In this proposal they are ctx->arg1 and ctx->arg2. > I've considered having different bpf_context's for every event, but > the complexity explodes. I need to hack all event definitions and so on. > imo it's better to move complexity to userspace, so program author > or high level language abstracts these details. I still don't understand why making them long instead of u64 is helpful, though. I feel like I'm missing obvious here. -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
