This series adds support attaching freplace BPF programs to multiple targets. This is needed to support incremental attachment of multiple XDP programs using the libxdp dispatcher model. The first three patches are refactoring patches: The first one is a trivial change to the logging in the verifier, split out to make the subsequent refactor easier to read. Patch 2 refactors check_attach_btf_id() so that the checks on program and target compatibility can be reused when attaching to a secondary location. Patch 3 changes prog_aux->linked_prog to be an embedded bpf_tracing_link that is initialised at program load time. This nicely encapsulates both the trampoline and the prog reference, and moves the release of these references into bpf_link teardown. At attach time, it will be removed from the extension prog, and primed as a regular bpf_link. Based on these refactorings, it becomes pretty straight-forward to support multiple-attach for freplace programs (patch 4). This is simply a matter of creating a second bpf_tracing_link if a target is supplied. However, for API consistency with other types of link attach, this option is added to the BPF_LINK_CREATE API instead of extending bpf_raw_tracepoint_open(). Patch 5 is a port of Jiri Olsa's patch to support fentry/fexit on freplace programs. His approach of getting the target type from the target program reference no longer works after we've gotten rid of linked_prog (because the bpf_tracing_link reference disappears on attach). Instead, we used the saved reference to the target prog type that is also used to verify compatibility on secondary freplace attachment. Patches 6 is the accompanying libbpf update, and patches 7-8 are selftests, the first one for the multi-freplace functionality itself, and the second one is Jiri's previous selftest for the fentry-to-freplace fix. With this series, libxdp and xdp-tools can successfully attach multiple programs one at a time. To play with this, use the 'freplace-multi-attach' branch of xdp-tools: $ git clone --recurse-submodules --branch freplace-multi-attach https://github.com/xdp-project/xdp-tools $ cd xdp-tools $ make $ sudo ./xdp-loader/xdp-loader load veth0 lib/testing/xdp_drop.o $ sudo ./xdp-loader/xdp-loader load veth0 lib/testing/xdp_pass.o $ sudo ./xdp-loader/xdp-loader status The series is also available here: https://git.kernel.org/pub/scm/linux/kernel/git/toke/linux.git/log/?h=bpf-freplace-multi-attach-alt-04 Changelog: v4: - Cleanup the refactored check_attach_btf_id() to make the logic easier to follow - Fix cleanup paths for bpf_tracing_link - Use xchg() for removing the bpf_tracing_link from prog->aux and restore on (some) failures - Use BPF_LINK_CREATE operation to create link with target instead of extending raw_tracepoint_open - Fold update of tools/ UAPI header into main patch - Update arg dereference patch to use skeletons and set_attach_target() v3: - Get rid of prog_aux->linked_prog entirely in favour of a bpf_tracing_link - Incorporate Jiri's fix for attaching fentry to freplace programs v2: - Drop the log arguments from bpf_raw_tracepoint_open - Fix kbot errors - Rebase to latest bpf-next --- Toke Høiland-Jørgensen (8): bpf: change logging calls from verbose() to bpf_log() and use log pointer bpf: verifier: refactor check_attach_btf_id() bpf: wrap prog->aux->linked_prog in a bpf_tracing_link bpf: support attaching freplace programs to multiple attach points bpf: Fix context type resolving for extension programs libbpf: add support for freplace attachment in bpf_link_create selftests: add test for multiple attachments of freplace program selftests/bpf: Adding test for arg dereference in extension trace include/linux/bpf.h | 33 ++- include/linux/bpf_verifier.h | 9 + include/uapi/linux/bpf.h | 2 + kernel/bpf/btf.c | 22 +- kernel/bpf/core.c | 4 +- kernel/bpf/syscall.c | 180 +++++++++++++-- kernel/bpf/trampoline.c | 32 ++- kernel/bpf/verifier.c | 215 +++++++++++------- tools/include/uapi/linux/bpf.h | 2 + tools/lib/bpf/bpf.c | 1 + tools/lib/bpf/bpf.h | 3 +- tools/lib/bpf/libbpf.c | 24 +- tools/lib/bpf/libbpf.h | 3 + tools/lib/bpf/libbpf.map | 1 + .../selftests/bpf/prog_tests/fexit_bpf2bpf.c | 171 +++++++++++--- .../selftests/bpf/prog_tests/trace_ext.c | 113 +++++++++ .../bpf/progs/freplace_get_constant.c | 15 ++ .../selftests/bpf/progs/test_trace_ext.c | 18 ++ .../bpf/progs/test_trace_ext_tracing.c | 25 ++ 19 files changed, 701 insertions(+), 172 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/trace_ext.c create mode 100644 tools/testing/selftests/bpf/progs/freplace_get_constant.c create mode 100644 tools/testing/selftests/bpf/progs/test_trace_ext.c create mode 100644 tools/testing/selftests/bpf/progs/test_trace_ext_tracing.c
