libbpf: Rewrite btf datasec names starting from '?'
Optional struct_ops maps are defined using question mark at the start of the section name, e.g.: SEC("?.struct_ops") struct test_ops optional_map = { ... }; This commit teaches libbpf to detect if kernel allows '?' prefix in datasec names, and if it doesn't then to rewrite such names by replacing '?' with '_', e.g.: DATASEC ?.struct_ops -> DATASEC _.struct_ops Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20240306104529.6453-13-eddyz87@gmail.com
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@ -147,6 +147,25 @@ static int probe_kern_btf_datasec(int token_fd)
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strs, sizeof(strs), token_fd));
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}
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static int probe_kern_btf_qmark_datasec(int token_fd)
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{
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static const char strs[] = "\0x\0?.data";
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/* static int a; */
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__u32 types[] = {
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/* int */
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BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
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/* VAR x */ /* [2] */
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BTF_TYPE_ENC(1, BTF_INFO_ENC(BTF_KIND_VAR, 0, 0), 1),
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BTF_VAR_STATIC,
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/* DATASEC ?.data */ /* [3] */
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BTF_TYPE_ENC(3, BTF_INFO_ENC(BTF_KIND_DATASEC, 0, 1), 4),
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BTF_VAR_SECINFO_ENC(2, 0, 4),
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};
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return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),
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strs, sizeof(strs), token_fd));
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}
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static int probe_kern_btf_float(int token_fd)
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{
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static const char strs[] = "\0float";
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@ -534,6 +553,9 @@ static struct kern_feature_desc {
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[FEAT_ARG_CTX_TAG] = {
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"kernel-side __arg_ctx tag", probe_kern_arg_ctx_tag,
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},
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[FEAT_BTF_QMARK_DATASEC] = {
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"BTF DATASEC names starting from '?'", probe_kern_btf_qmark_datasec,
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},
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};
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bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id)
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@ -2869,6 +2869,11 @@ static bool section_have_execinstr(struct bpf_object *obj, int idx)
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return sh->sh_flags & SHF_EXECINSTR;
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}
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static bool starts_with_qmark(const char *s)
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{
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return s && s[0] == '?';
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}
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static bool btf_needs_sanitization(struct bpf_object *obj)
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{
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bool has_func_global = kernel_supports(obj, FEAT_BTF_GLOBAL_FUNC);
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@ -2878,9 +2883,10 @@ static bool btf_needs_sanitization(struct bpf_object *obj)
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bool has_decl_tag = kernel_supports(obj, FEAT_BTF_DECL_TAG);
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bool has_type_tag = kernel_supports(obj, FEAT_BTF_TYPE_TAG);
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bool has_enum64 = kernel_supports(obj, FEAT_BTF_ENUM64);
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bool has_qmark_datasec = kernel_supports(obj, FEAT_BTF_QMARK_DATASEC);
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return !has_func || !has_datasec || !has_func_global || !has_float ||
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!has_decl_tag || !has_type_tag || !has_enum64;
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!has_decl_tag || !has_type_tag || !has_enum64 || !has_qmark_datasec;
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}
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static int bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
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@ -2892,6 +2898,7 @@ static int bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
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bool has_decl_tag = kernel_supports(obj, FEAT_BTF_DECL_TAG);
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bool has_type_tag = kernel_supports(obj, FEAT_BTF_TYPE_TAG);
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bool has_enum64 = kernel_supports(obj, FEAT_BTF_ENUM64);
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bool has_qmark_datasec = kernel_supports(obj, FEAT_BTF_QMARK_DATASEC);
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int enum64_placeholder_id = 0;
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struct btf_type *t;
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int i, j, vlen;
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@ -2918,7 +2925,7 @@ static int bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
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name = (char *)btf__name_by_offset(btf, t->name_off);
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while (*name) {
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if (*name == '.')
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if (*name == '.' || *name == '?')
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*name = '_';
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name++;
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}
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@ -2933,6 +2940,14 @@ static int bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
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vt = (void *)btf__type_by_id(btf, v->type);
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m->name_off = vt->name_off;
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}
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} else if (!has_qmark_datasec && btf_is_datasec(t) &&
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starts_with_qmark(btf__name_by_offset(btf, t->name_off))) {
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/* replace '?' prefix with '_' for DATASEC names */
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char *name;
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name = (char *)btf__name_by_offset(btf, t->name_off);
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if (name[0] == '?')
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name[0] = '_';
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} else if (!has_func && btf_is_func_proto(t)) {
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/* replace FUNC_PROTO with ENUM */
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vlen = btf_vlen(t);
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@ -374,6 +374,8 @@ enum kern_feature_id {
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FEAT_UPROBE_MULTI_LINK,
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/* Kernel supports arg:ctx tag (__arg_ctx) for global subprogs natively */
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FEAT_ARG_CTX_TAG,
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/* Kernel supports '?' at the front of datasec names */
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FEAT_BTF_QMARK_DATASEC,
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__FEAT_CNT,
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};
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