From: David Vernet <void@manifault.com> mainline inclusion from mainline-v6.8-rc1 commit 8b7b0e5fe47de90ba6c350f9abece589fb637f79 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/IDC9YK Reference: https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commi... -------------------------------- In libbpf, when determining whether we need to load vmlinux btf, we're currently (among other things) checking whether there is any struct_ops program present in the object. This works for most realistic struct_ops maps, as a struct_ops map is of course typically composed of one or more struct_ops programs. However, that technically need not be the case. A struct_ops interface could be defined which allows a map to be specified which one or more non-prog fields, and which provides default behavior if no struct_ops progs is actually provided otherwise. For sched_ext, for example, you technically only need to specify the name of the scheduler in the struct_ops map, with the core scheduler logic providing default behavior if no prog is actually specified. If we were to define and try to load such a struct_ops map, we would crash in libbpf when initializing it as obj->btf_vmlinux will be NULL: Reading symbols from minimal... (gdb) r Starting program: minimal_example [Thread debugging using libthread_db enabled] Using host libthread_db library "/usr/lib/libthread_db.so.1". Program received signal SIGSEGV, Segmentation fault. 0x000055555558308c in btf__type_cnt (btf=0x0) at btf.c:612 612 return btf->start_id + btf->nr_types; (gdb) bt type_name=0x5555555d99e3 "sched_ext_ops", kind=4) at btf.c:914 kind=4) at btf.c:942 type=0x7fffffffe558, type_id=0x7fffffffe548, ... data_member=0x7fffffffe568) at libbpf.c:948 kern_btf=0x0) at libbpf.c:1017 at libbpf.c:8059 So as to account for such bare-bones struct_ops maps, let's update obj_needs_vmlinux_btf() to also iterate over an obj's maps and check whether any of them are struct_ops maps. Signed-off-by: David Vernet <void@manifault.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Reviewed-by: Alan Maguire <alan.maguire@oracle.com> Link: https://lore.kernel.org/bpf/20231208061704.400463-1-void@manifault.com Signed-off-by: Zicheng Qu <quzicheng@huawei.com> --- tools/lib/bpf/libbpf.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 2f6fd4a2f37d..4f058925aa72 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -3082,9 +3082,15 @@ static bool prog_needs_vmlinux_btf(struct bpf_program *prog) return false; } +static bool map_needs_vmlinux_btf(struct bpf_map *map) +{ + return bpf_map__is_struct_ops(map); +} + static bool obj_needs_vmlinux_btf(const struct bpf_object *obj) { struct bpf_program *prog; + struct bpf_map *map; int i; /* CO-RE relocations need kernel BTF, only when btf_custom_path @@ -3109,6 +3115,11 @@ static bool obj_needs_vmlinux_btf(const struct bpf_object *obj) return true; } + bpf_object__for_each_map(map, obj) { + if (map_needs_vmlinux_btf(map)) + return true; + } + return false; } -- 2.34.1