iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

libbpf: Rewrite btf datasec names starting from '?'

Browse Source 
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 5ad0ecbe05
commit 6ebaa3fb88
3 changed files with 41 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
tools/lib/bpf/features.c
View File

@ -147,6 +147,25 @@ static int probe_kern_btf_datasec(int token_fd)
strs, sizeof(strs), token_fd));
}
static int probe_kern_btf_qmark_datasec(int token_fd)
{
static const char strs[] = "\0x\0?.data";
/* static int a; */
__u32 types[] = {
/* int */
BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
/* VAR x */ /* [2] */
BTF_TYPE_ENC(1, BTF_INFO_ENC(BTF_KIND_VAR, 0, 0), 1),
BTF_VAR_STATIC,
/* DATASEC ?.data */ /* [3] */
BTF_TYPE_ENC(3, BTF_INFO_ENC(BTF_KIND_DATASEC, 0, 1), 4),
BTF_VAR_SECINFO_ENC(2, 0, 4),
};
return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),
strs, sizeof(strs), token_fd));
}
static int probe_kern_btf_float(int token_fd)
{
static const char strs[] = "\0float";
@ -534,6 +553,9 @@ static struct kern_feature_desc {
[FEAT_ARG_CTX_TAG] = {
"kernel-side __arg_ctx tag", probe_kern_arg_ctx_tag,
},
[FEAT_BTF_QMARK_DATASEC] = {
"BTF DATASEC names starting from '?'", probe_kern_btf_qmark_datasec,
},
};
bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id)

19
tools/lib/bpf/libbpf.c
View File

@ -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);

2
tools/lib/bpf/libbpf_internal.h
View File

@ -374,6 +374,8 @@ enum kern_feature_id {
FEAT_UPROBE_MULTI_LINK,
/* Kernel supports arg:ctx tag (__arg_ctx) for global subprogs natively */
FEAT_ARG_CTX_TAG,
/* Kernel supports '?' at the front of datasec names */
FEAT_BTF_QMARK_DATASEC,
__FEAT_CNT,
};