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libbpf: Rewrite btf datasec names starting from '?'

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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
This commit is contained in:
Eduard Zingerman
2024-03-06 12:45:26 +02:00
committed by Andrii Nakryiko
parent fc8b86bda2
commit 438adf417d
3 changed files with 41 additions and 2 deletions
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19
src/libbpf.c
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@@ -2869,6 +2869,11 @@ static bool section_have_execinstr(struct bpf_object *obj, int idx)
return sh->sh_flags & SHF_EXECINSTR;
}
static bool starts_with_qmark(const char *s)
{
return s && s[0] == '?';
}
static bool btf_needs_sanitization(struct bpf_object *obj)
{
bool has_func_global = kernel_supports(obj, FEAT_BTF_GLOBAL_FUNC);
@@ -2878,9 +2883,10 @@ static bool btf_needs_sanitization(struct bpf_object *obj)
bool has_decl_tag = kernel_supports(obj, FEAT_BTF_DECL_TAG);
bool has_type_tag = kernel_supports(obj, FEAT_BTF_TYPE_TAG);
bool has_enum64 = kernel_supports(obj, FEAT_BTF_ENUM64);
bool has_qmark_datasec = kernel_supports(obj, FEAT_BTF_QMARK_DATASEC);
return !has_func || !has_datasec || !has_func_global || !has_float ||
!has_decl_tag || !has_type_tag || !has_enum64;
!has_decl_tag || !has_type_tag || !has_enum64 || !has_qmark_datasec;
}
static int bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
@@ -2892,6 +2898,7 @@ static int bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
bool has_decl_tag = kernel_supports(obj, FEAT_BTF_DECL_TAG);
bool has_type_tag = kernel_supports(obj, FEAT_BTF_TYPE_TAG);
bool has_enum64 = kernel_supports(obj, FEAT_BTF_ENUM64);
bool has_qmark_datasec = kernel_supports(obj, FEAT_BTF_QMARK_DATASEC);
int enum64_placeholder_id = 0;
struct btf_type *t;
int i, j, vlen;
@@ -2918,7 +2925,7 @@ static int bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
name = (char *)btf__name_by_offset(btf, t->name_off);
while (*name) {
if (*name == '.')
if (*name == '.' || *name == '?')
*name = '_';
name++;
}
@@ -2933,6 +2940,14 @@ static int bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
vt = (void *)btf__type_by_id(btf, v->type);
m->name_off = vt->name_off;
}
} else if (!has_qmark_datasec && btf_is_datasec(t) &&
starts_with_qmark(btf__name_by_offset(btf, t->name_off))) {
/* replace '?' prefix with '_' for DATASEC names */
char *name;
name = (char *)btf__name_by_offset(btf, t->name_off);
if (name[0] == '?')
name[0] = '_';
} else if (!has_func && btf_is_func_proto(t)) {
/* replace FUNC_PROTO with ENUM */
vlen = btf_vlen(t);