On 7/16/21 12:51 PM, Andrii Nakryiko wrote:
On Tue, Jul 13, 2021 at 5:43 AM Shuyi Cheng <chengshuyi@xxxxxxxxxxxxxxxxx> wrote:btf_custom_path allows developers to load custom BTF, and subsequent CO-RE will use custom BTF for relocation. Learn from Andrii's comments in [0], add the btf_custom_path parameter to bpf_obj_open_opts, you can directly use the skeleton's <objname>_bpf__open_opts function to pass in the btf_custom_path parameter. Prior to this, there was also a developer who provided a patch with similar functions. It is a pity that the follow-up did not continue to advance. See [1]. [0]https://lore.kernel.org/bpf/CAEf4BzbJZLjNoiK8_VfeVg_Vrg=9iYFv+po-38SMe=UzwDKJ=Q@xxxxxxxxxxxxxx/#t [1]https://yhbt.net/lore/all/CAEf4Bzbgw49w2PtowsrzKQNcxD4fZRE6AKByX-5-dMo-+oWHHA@xxxxxxxxxxxxxx/ Signed-off-by: Shuyi Cheng <chengshuyi@xxxxxxxxxxxxxxxxx> --- tools/lib/bpf/libbpf.c | 36 ++++++++++++++++++++++++++++++------ tools/lib/bpf/libbpf.h | 9 ++++++++- 2 files changed, 38 insertions(+), 7 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 1e04ce7..6e11a7b 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -498,6 +498,13 @@ struct bpf_object { * it at load time. */ struct btf *btf_vmlinux; + /* Path to the custom BTF to be used for BPF CO-RE relocations. + * This custom BTF completely replaces the use of vmlinux BTF + * for the purpose of CO-RE relocations. + * NOTE: any other BPF feature (e.g., fentry/fexit programs, + * struct_ops, etc) will need actual kernel BTF at /sys/kernel/btf/vmlinux. + */this comment completely duplicates the one from bpf_object_open_opts, I'll remove or shorten it+ char *btf_custom_path; /* vmlinux BTF override for CO-RE relocations */ struct btf *btf_vmlinux_override; /* Lazily initialized kernel module BTFs */ @@ -2645,10 +2652,6 @@ static bool obj_needs_vmlinux_btf(const struct bpf_object *obj) struct bpf_program *prog; int i; - /* CO-RE relocations need kernel BTF */ - if (obj->btf_ext && obj->btf_ext->core_relo_info.len) - return true; - /* Support for typed ksyms needs kernel BTF */ for (i = 0; i < obj->nr_extern; i++) { const struct extern_desc *ext; @@ -2665,6 +2668,13 @@ static bool obj_needs_vmlinux_btf(const struct bpf_object *obj) return true; } + /* CO-RE relocations need kernel BTF, only when btf_custom_path + * is not specified + */ + if (obj->btf_ext && obj->btf_ext->core_relo_info.len + && !obj->btf_custom_path) + return true;not sure why you moved it, I'll move it back to minimize code churn
You're right. 👍 regards, Shuyi
+ return false; }[...]
