On 03/01/2019 09:25 PM, Yonghong Song wrote: > On 3/1/19 12:06 PM, Daniel Borkmann wrote: >> On 03/01/2019 08:19 PM, Yonghong Song wrote: >>> On 3/1/19 11:10 AM, Andrii Nakryiko wrote: >>>> On Fri, Mar 1, 2019 at 10:58 AM Yonghong Song <yhs@xxxxxx> wrote: >>>>> On 3/1/19 10:48 AM, Andrii Nakryiko wrote: >>>>>> On Fri, Mar 1, 2019 at 10:31 AM Yonghong Song <yhs@xxxxxx> wrote: >>>>>>> On 2/28/19 3:18 PM, Daniel Borkmann wrote: >> [...] >>>>>> Would it be reasonable to just plain disable usage of uninitialized >>>>>> global variables, as it kind of goes against BPF's philosophy that >>>>>> everything should be written to, before can be read? So while we can >>>>>> just implicitly zero-out everything beforehand, it might be a good >>>>>> idea to remind and enforce that explictly? >>>>> >>>>> There will be a verifier error, so the program with "int g" will not >>>>> run, the same as today. >>>> >>>> Yeah, I understand, but with pretty obscure error about not supporting >>>> relocations and stuff, right? >>>> >>>>> >>>>> We could improve by flagging the error at compiler error or libbpf time. >>>> >>>> So that's my point, that having compiler emit nicer error for >>>> target=bpf would be nice touch to user experience :) >>> >>> I just removed a compiler error for static variables... >>> >>> I will wait for this patch lands, hear people complains (either need to >>> support "int g;" or need better error messages, etc.) and then decide >>> what next to do ... >> >> By the way, from LLVM side, do you think it makes sense for local vars >> where you encode the offset into insn->imm to already encode it into >> (insn+1)->imm of the ldimm64, so that loaders can just pass this offset >> through instead of fixing it up like I did? I'm fine either way though, >> just thought might be worth pointing out while we're at it. :) > > Yes, llvm can do that. Let me prototype it and will let you know > if it landed in llvm trunk. Awesome, thanks!
