From bb8ffe61ea454a565e4fb1f450ef71237c9f032c Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Fri, 11 Feb 2022 21:57:32 -0800 Subject: [PATCH 1/2] bpftool: Add C++-specific open/load/etc skeleton wrappers Add C++-specific static methods for code-generated BPF skeleton for each skeleton operation: open, open_opts, open_and_load, load, attach, detach, destroy, and elf_bytes. This is to facilitate easier C++ templating on top of pure C BPF skeleton. In C, open/load/destroy/etc "methods" are of the form __() to avoid name collision with similar "methods" of other skeletons withint the same application. This works well, but is very inconvenient for C++ applications that would like to write generic (templated) wrappers around BPF skeleton to fit in with C++ code base and take advantage of destructors and other convenient C++ constructs. This patch makes it easier to build such generic templated wrappers by additionally defining C++ static methods for skeleton's struct with fixed names. This allows to refer to, say, open method as `T::open()` instead of having to somehow generate `T__open()` function call. Next patch adds an example template to test_cpp selftest to demonstrate how it's possible to have all the operations wrapped in a generic Skeleton type without explicitly passing function references. An example of generated declaration section without %1$s placeholders: #ifdef __cplusplus static struct test_attach_probe *open(const struct bpf_object_open_opts *opts = nullptr); static struct test_attach_probe *open_and_load(); static int load(struct test_attach_probe *skel); static int attach(struct test_attach_probe *skel); static void detach(struct test_attach_probe *skel); static void destroy(struct test_attach_probe *skel); static const void *elf_bytes(size_t *sz); #endif /* __cplusplus */ Signed-off-by: Andrii Nakryiko Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20220212055733.539056-2-andrii@kernel.org --- tools/bpf/bpftool/gen.c | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-) diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c index 6f2e20be0c62..022f30490567 100644 --- a/tools/bpf/bpftool/gen.c +++ b/tools/bpf/bpftool/gen.c @@ -831,6 +831,16 @@ static int do_skeleton(int argc, char **argv) codegen("\ \n\ + \n\ + #ifdef __cplusplus \n\ + static struct %1$s *open(const struct bpf_object_open_opts *opts = nullptr);\n\ + static struct %1$s *open_and_load(); \n\ + static int load(struct %1$s *skel); \n\ + static int attach(struct %1$s *skel); \n\ + static void detach(struct %1$s *skel); \n\ + static void destroy(struct %1$s *skel); \n\ + static const void *elf_bytes(size_t *sz); \n\ + #endif /* __cplusplus */ \n\ }; \n\ \n\ static void \n\ @@ -1025,9 +1035,19 @@ static int do_skeleton(int argc, char **argv) \"; \n\ } \n\ \n\ - #endif /* %s */ \n\ + #ifdef __cplusplus \n\ + struct %1$s *%1$s::open(const struct bpf_object_open_opts *opts) { return %1$s__open_opts(opts); }\n\ + struct %1$s *%1$s::open_and_load() { return %1$s__open_and_load(); } \n\ + int %1$s::load(struct %1$s *skel) { return %1$s__load(skel); } \n\ + int %1$s::attach(struct %1$s *skel) { return %1$s__attach(skel); } \n\ + void %1$s::detach(struct %1$s *skel) { %1$s__detach(skel); } \n\ + void %1$s::destroy(struct %1$s *skel) { %1$s__destroy(skel); } \n\ + const void *%1$s::elf_bytes(size_t *sz) { return %1$s__elf_bytes(sz); } \n\ + #endif /* __cplusplus */ \n\ + \n\ + #endif /* %2$s */ \n\ ", - header_guard); + obj_name, header_guard); err = 0; out: bpf_object__close(obj); From 189e0ecabc1717db62deab751afa755f07bdbcf8 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Fri, 11 Feb 2022 21:57:33 -0800 Subject: [PATCH 2/2] selftests/bpf: Add Skeleton templated wrapper as an example Add an example of how to build C++ template-based BPF skeleton wrapper. It's an actually runnable valid use of skeleton through more C++-like interface. Note that skeleton destuction happens implicitly through Skeleton's destructor. Also make test_cpp runnable as it would have crashed on invalid btf passed into btf_dump__new(). Signed-off-by: Andrii Nakryiko Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20220212055733.539056-3-andrii@kernel.org --- tools/testing/selftests/bpf/test_cpp.cpp | 87 +++++++++++++++++++++++- 1 file changed, 85 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/bpf/test_cpp.cpp b/tools/testing/selftests/bpf/test_cpp.cpp index e00201de2890..773f165c4898 100644 --- a/tools/testing/selftests/bpf/test_cpp.cpp +++ b/tools/testing/selftests/bpf/test_cpp.cpp @@ -5,18 +5,100 @@ #include #include "test_core_extern.skel.h" -/* do nothing, just make sure we can link successfully */ +template +class Skeleton { +private: + T *skel; +public: + Skeleton(): skel(nullptr) { } + + ~Skeleton() { if (skel) T::destroy(skel); } + + int open(const struct bpf_object_open_opts *opts = nullptr) + { + int err; + + if (skel) + return -EBUSY; + + skel = T::open(opts); + err = libbpf_get_error(skel); + if (err) { + skel = nullptr; + return err; + } + + return 0; + } + + int load() { return T::load(skel); } + + int attach() { return T::attach(skel); } + + void detach() { return T::detach(skel); } + + const T* operator->() const { return skel; } + + T* operator->() { return skel; } + + const T *get() const { return skel; } +}; static void dump_printf(void *ctx, const char *fmt, va_list args) { } +static void try_skeleton_template() +{ + Skeleton skel; + std::string prog_name; + int err; + LIBBPF_OPTS(bpf_object_open_opts, opts); + + err = skel.open(&opts); + if (err) { + fprintf(stderr, "Skeleton open failed: %d\n", err); + return; + } + + skel->data->kern_ver = 123; + skel->data->int_val = skel->data->ushort_val; + + err = skel.load(); + if (err) { + fprintf(stderr, "Skeleton load failed: %d\n", err); + return; + } + + if (!skel->kconfig->CONFIG_BPF_SYSCALL) + fprintf(stderr, "Seems like CONFIG_BPF_SYSCALL isn't set?!\n"); + + err = skel.attach(); + if (err) { + fprintf(stderr, "Skeleton attach failed: %d\n", err); + return; + } + + prog_name = bpf_program__name(skel->progs.handle_sys_enter); + if (prog_name != "handle_sys_enter") + fprintf(stderr, "Unexpected program name: %s\n", prog_name.c_str()); + + bpf_link__destroy(skel->links.handle_sys_enter); + skel->links.handle_sys_enter = bpf_program__attach(skel->progs.handle_sys_enter); + + skel.detach(); + + /* destructor will destory underlying skeleton */ +} + int main(int argc, char *argv[]) { struct btf_dump_opts opts = { }; struct test_core_extern *skel; struct btf *btf; + try_skeleton_template(); + /* libbpf.h */ libbpf_set_print(NULL); @@ -25,7 +107,8 @@ int main(int argc, char *argv[]) /* btf.h */ btf = btf__new(NULL, 0); - btf_dump__new(btf, dump_printf, nullptr, &opts); + if (!libbpf_get_error(btf)) + btf_dump__new(btf, dump_printf, nullptr, &opts); /* BPF skeleton */ skel = test_core_extern__open_and_load();