On Sun, Jan 28, 2024 at 5:35 PM Daniel Xu <dxu@xxxxxxxxx> wrote: > > This patch enables dumping kfunc prototypes from bpftool. This is useful > b/c with this patch, end users will no longer have to manually define > kfunc prototypes. For the kernel tree, this also means we can drop > kfunc prototypes from: > > tools/testing/selftests/bpf/bpf_kfuncs.h > tools/testing/selftests/bpf/bpf_experimental.h > > Example usage: > > $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux > > $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3 > extern void cgroup_rstat_updated(struct cgroup * cgrp, int cpu) __ksym; > extern void cgroup_rstat_flush(struct cgroup * cgrp) __ksym; > extern struct bpf_key * bpf_lookup_user_key(u32 serial, u64 flags) __ksym; > All kfuncs have to be declared __weak, otherwise it will be impossible to feature-detect them in BPF code > Note that this patch is only effective after enabling pahole [0] > and kernel [1] changes are merged. > > [0]: https://lore.kernel.org/bpf/0f25134ec999e368478c4ca993b3b729c2a03383.1706491733.git.dxu@xxxxxxxxx/ > [1]: https://lore.kernel.org/bpf/cover.1706491398.git.dxu@xxxxxxxxx/ > > Signed-off-by: Daniel Xu <dxu@xxxxxxxxx> > --- > tools/bpf/bpftool/btf.c | 29 +++++++++++++++++++++++++++++ > 1 file changed, 29 insertions(+) > > diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c > index 91fcb75babe3..9ab26ed12733 100644 > --- a/tools/bpf/bpftool/btf.c > +++ b/tools/bpf/bpftool/btf.c > @@ -20,6 +20,8 @@ > #include "json_writer.h" > #include "main.h" > > +#define KFUNC_DECL_TAG "bpf_kfunc" > + > static const char * const btf_kind_str[NR_BTF_KINDS] = { > [BTF_KIND_UNKN] = "UNKNOWN", > [BTF_KIND_INT] = "INT", > @@ -454,6 +456,28 @@ static int dump_btf_raw(const struct btf *btf, > return 0; > } > > +static void dump_btf_kfuncs(const struct btf *btf) > +{ > + int cnt = btf__type_cnt(btf); > + int i; > + > + for (i = 1; i < cnt; i++) { > + const struct btf_type *t = btf__type_by_id(btf, i); > + char kfunc_sig[1024]; > + const char *name; > + > + if (!btf_is_decl_tag(t)) > + continue; > + > + name = btf__name_by_offset(btf, t->name_off); > + if (strncmp(name, KFUNC_DECL_TAG, sizeof(KFUNC_DECL_TAG))) > + continue; > + > + btf_dumper_type_only(btf, t->type, kfunc_sig, sizeof(kfunc_sig)); > + printf("extern %s __ksym;\n\n", kfunc_sig); > + } > +} > + > static void __printf(2, 0) btf_dump_printf(void *ctx, > const char *fmt, va_list args) > { > @@ -476,6 +500,9 @@ static int dump_btf_c(const struct btf *btf, > printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n"); > printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n"); > printf("#endif\n\n"); > + printf("#ifndef __ksym\n"); > + printf("#define __ksym __attribute__((section(\".ksyms\")))\n"); > + printf("#endif\n\n"); > > if (root_type_cnt) { > for (i = 0; i < root_type_cnt; i++) { > @@ -491,6 +518,8 @@ static int dump_btf_c(const struct btf *btf, > if (err) > goto done; > } > + > + dump_btf_kfuncs(btf); > } > > printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n"); > -- > 2.42.1 >
