On Thu, Jan 13, 2022 at 2:30 AM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote: > > On Wed, 12 Jan 2022, Andrii Nakryiko wrote: > > > On Wed, Jan 12, 2022 at 8:19 AM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote: > > > > > > This patch series is a rough attempt to support attach by name for > > > uprobes and USDT (Userland Static Defined Tracing) probes. > > > Currently attach for such probes is done by determining the offset > > > manually, so the aim is to try and mimic the simplicity of kprobe > > > attach, making use of uprobe opts. > > > > > > One restriction applies: uprobe attach supports system-wide probing > > > by specifying "-1" for the pid. That functionality is not supported, > > > since we need a running process to determine the base address to > > > subtract to get the uprobe-friendly offset. There may be a way > > > to do this without a running process, so any suggestions would > > > be greatly appreciated. > > > > > > There are probably a bunch of subtleties missing here; the aim > > > is to see if this is useful and if so hopefully we can refine > > > it to deal with more complex cases. I tried to handle one case > > > that came to mind - weak library symbols - but there are probably > > > other issues when determining which address to use I haven't > > > thought of. > > > > > > Alan Maguire (4): > > > libbpf: support function name-based attach for uprobes > > > libbpf: support usdt provider/probe name-based attach for uprobes > > > selftests/bpf: add tests for u[ret]probe attach by name > > > selftests/bpf: add test for USDT uprobe attach by name > > > > > > > Hey Alan, > > > > I've been working on USDT support last year. It's considerably more > > code than in this RFC, but it handles not just finding a location of > > USDT probe(s), but also fetching its arguments based on argument > > location specification and more usability focused BPF-side APIs to > > work with USDTs. > > > > I don't remember how up to date it is, but the last "open source" > > version of it can be found at [0]. I currently have the latest > > debugged and tested version internally in the process of being > > integrated into our profiling solution here at Meta. So far it seems > > to be working fine and covers our production use cases well. > > > > This looks great Andrii! I really like the argument access work, and the > global tracing part is solved too by using the ELF segment info instead > of the process maps to get the relative offset, with (I think?) use of > BPF cookies to disambiguate between different user attachments. BPF cookies are mandatory for when attaching to a shared library *and* NOT specifying PID. This is actually the mode that BCC doesn't seem to support. In all other cases BPF cookie shouldn't be mandatory. > > The one piece that seems to be missing from my perspective - and this may > be in more recent versions - is uprobe function attachment by name. Most of > the work is already done in libusdt so it's reasonably doable I think - at a > minimum it would require an equivalent to the find_elf_func_offset() > function in my patch 1. Now the name of the library libusdt suggests its > focus is on USDT of course, but I think having userspace function attach > by name too would be great. Is that part of your plans for this work? True, uprobes don't supprot attaching by function name, which is quite annoying. It's certainly not a focus for libusdt (or whatever it will end up being called when open-sources). But if it's not much code and complexity we should probably just add that to libbpf directly for uprobes. > > Thanks! > > Alan
