| Message ID | 20210830173424.1385796-5-memxor@gmail.com (mailing list archive) |
|---|---|
| State | RFC |
| Delegated to: | BPF |
| Headers | show |
| Series | Support kernel module function calls from eBPF | expand |
| Context | Check | Description |
|---|---|---|
| bpf/vmtest-bpf-next | pending | Kernel LATEST + selftests |
| netdev/cover_letter | success | Link |
| netdev/fixes_present | success | Link |
| netdev/patch_count | success | Link |
| netdev/tree_selection | success | Clearly marked for bpf-next |
| netdev/subject_prefix | success | Link |
| netdev/cc_maintainers | warning | 2 maintainers not CCed: kpsingh@kernel.org john.fastabend@gmail.com |
| netdev/source_inline | success | Was 0 now: 0 |
| netdev/verify_signedoff | success | Link |
| netdev/module_param | success | Was 0 now: 0 |
| netdev/build_32bit | success | Errors and warnings before: 0 this patch: 0 |
| netdev/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| netdev/verify_fixes | success | Link |
| netdev/checkpatch | warning | CHECK: multiple assignments should be avoided |
| netdev/build_allmodconfig_warn | success | Errors and warnings before: 0 this patch: 0 |
| netdev/header_inline | success | Link |
On Mon, Aug 30, 2021 at 10:34 AM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote: > > Preserve these calls as it allows verifier to succeed in loading the > program if they are determined to be unreachable after dead code > elimination during program load. If not, the verifier will fail at > runtime. > This should be controlled by whether extern for func is weak or not, just like we do for variables (see bpf_object__resolve_ksym_var_btf_id()). > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> > --- > tools/lib/bpf/libbpf.c | 20 ++++++++++++++++---- > 1 file changed, 16 insertions(+), 4 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index c4677ef97caa..9df90098f111 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -6736,9 +6736,14 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj, > kfunc_id = find_ksym_btf_id(obj, ext->name, BTF_KIND_FUNC, > &kern_btf, &kern_btf_fd); > if (kfunc_id < 0) { > - pr_warn("extern (func ksym) '%s': not found in kernel BTF\n", > + pr_warn("extern (func ksym) '%s': not found in kernel BTF, encoding btf_id as 0\n", > ext->name); > - return kfunc_id; > + /* keep invalid kfuncs, so that verifier can load the program if > + * they get removed during DCE pass in the verifier. > + * The encoding must be insn->imm = 0, insn->off = 0. > + */ > + kfunc_id = kern_btf_fd = 0; > + goto resolve; > } > > if (kern_btf != obj->btf_vmlinux) { > @@ -6798,11 +6803,18 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj, > return -EINVAL; > } > > +resolve: > ext->is_set = true; > ext->ksym.kernel_btf_obj_fd = kern_btf_fd; > ext->ksym.kernel_btf_id = kfunc_id; > - pr_debug("extern (func ksym) '%s': resolved to kernel [%d]\n", > - ext->name, kfunc_id); > + if (kfunc_id) { > + pr_debug("extern (func ksym) '%s': resolved to kernel [%d]\n", > + ext->name, kfunc_id); > + } else { > + ext->ksym.offset = 0; > + pr_debug("extern (func ksym) '%s': added special invalid kfunc with imm = 0\n", > + ext->name); > + } > > return 0; > } > -- > 2.33.0 >
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index c4677ef97caa..9df90098f111 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -6736,9 +6736,14 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj, kfunc_id = find_ksym_btf_id(obj, ext->name, BTF_KIND_FUNC, &kern_btf, &kern_btf_fd); if (kfunc_id < 0) { - pr_warn("extern (func ksym) '%s': not found in kernel BTF\n", + pr_warn("extern (func ksym) '%s': not found in kernel BTF, encoding btf_id as 0\n", ext->name); - return kfunc_id; + /* keep invalid kfuncs, so that verifier can load the program if + * they get removed during DCE pass in the verifier. + * The encoding must be insn->imm = 0, insn->off = 0. + */ + kfunc_id = kern_btf_fd = 0; + goto resolve; } if (kern_btf != obj->btf_vmlinux) { @@ -6798,11 +6803,18 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj, return -EINVAL; } +resolve: ext->is_set = true; ext->ksym.kernel_btf_obj_fd = kern_btf_fd; ext->ksym.kernel_btf_id = kfunc_id; - pr_debug("extern (func ksym) '%s': resolved to kernel [%d]\n", - ext->name, kfunc_id); + if (kfunc_id) { + pr_debug("extern (func ksym) '%s': resolved to kernel [%d]\n", + ext->name, kfunc_id); + } else { + ext->ksym.offset = 0; + pr_debug("extern (func ksym) '%s': added special invalid kfunc with imm = 0\n", + ext->name); + } return 0; }
Preserve these calls as it allows verifier to succeed in loading the program if they are determined to be unreachable after dead code elimination during program load. If not, the verifier will fail at runtime. Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> --- tools/lib/bpf/libbpf.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-)