On Mon, Jan 4, 2021 at 7:29 AM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote: > > BPF Type Format (BTF) provides a description of kernel data structures > and of the types kernel functions utilize as arguments and return values. > > A helper was recently added - bpf_snprintf_btf() - that uses that > description to create a string representation of the data provided, > using the BTF id of its type. For example to create a string > representation of a "struct sk_buff", the pointer to the skb > is provided along with the type id of "struct sk_buff". > > Here that functionality is utilized to support tracing kernel > function entry and return using k[ret]probes. The "struct pt_regs" > context can be used to derive arguments and return values, and > when the user supplies a function name we > > - look it up in /proc/kallsyms to find its address/module > - look it up in the BTF kernel data to get types of arguments > and return value > - store a map representation of the trace information, keyed by > instruction pointer > - on function entry/return we look up the map to retrieve the BTF > ids of the arguments/return values and can call bpf_snprintf_btf() > with these argument/return values along with the type ids to store > a string representation in the map. > - this is then sent via perf event to userspace where it can be > displayed. > > ksnoop can be used to show function signatures; for example: This is definitely quite useful! Is it possible to integrate this with bpftrace? That would save people from learning yet another tool. ;) Thanks.
