On Mon, 11 Oct 2021 18:23:34 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Thu, 23 Sep 2021 21:39:43 +0900 > Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > > Hi Steve, > > > > Hi Masami, > > Sorry for the late reply, but Plumbers followed by OSS put me way behind, > and I just got to this email :-/ > > > Here I share my testing patch of the BTF for kprobe events. > > Currently this only allow user to specify '$$args' for > > tracing all arguments of the function. This is only > > avaialbe if > > - the probe point is on the function entry > > - the kernel is compiled with BTF (CONFIG_DEBUG_INFO_BTF) > > - the kernel is enables BPF (CONFIG_BPF_SYSCALL) > > > > And Special thanks to Sven! Most of BTF handling part of > > this patch comes from his patch [1] > > > > [1] https://stackframe.org/0001-ftrace-arg-hack.patch > > Which is newer than this patch because he sent a v2, and that's a couple > patches down in my queue. I'll be looking at that one shortly as well. Did he send his BTF hack patch to you ? I didn't notice that. > > What I thought while coding this were; > > - kernel/bpf/btf.c can be moved under lib/ so that > > the other subsystems can reuse it, independent > > from BPF. (Also, this should depends on CONFIG_DEBUG_INFO_BTF) > > Makes sense. > > > - some more utility functions can be exposed. > > e.g. I copied btf_type_int() from btf.c > > Agreed. > > > - If there are more comments for the BTF APIs, it will > > be more useful... > > - Overall, the BTF is easy to understand for who > > already understand DWARF. Great work! > > Great to hear. > > > - I think I need 'ptr' and 'bool' types for fetcharg types. > > > > Anyway, this is just for testing. I have to add some > > more cleanup, features and documentations, etc. > > This is awesome, and something to look at for a generic ftrace args point > of view too. > > One issue is how do we handle multiple register values? Like a u64 type on > 32 bit? As $arg1 is just a register that is in $arg1, for a u64 parameter > on 32 bit, that is usually handled with two registers. > > Have thoughts on that? Oh, that's a good point! The probe event supports such case, since I expected the user will use 2 arguments to record it. But indeed, using BTF means we need such extension. OK, let me consider how to extend fetchargs to support it. Thank you! > > I'll play with your patch today. > > -- Steve -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
