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. > > 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? I'll play with your patch today. -- Steve
