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libbpf: Support flexible arrays in CO-RE 

Some data stuctures in kernel are defined with either zero-sized array or
flexible (dimensionless) array at the end of a struct. Actual data of such
array follows in memory immediately after the end of that struct, forming its
variable-sized "body" of elements. Support such access pattern in CO-RE
relocation handling.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191215070844.1014385-2-andriin@fb.com
This commit is contained in:
Andrii Nakryiko 2019-12-14 23:08:43 -08:00 committed by Alexei Starovoitov
parent 01c6f7aaac
commit 1b484b301c
1 changed files with 29 additions and 5 deletions
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34
tools/lib/bpf/libbpf.c
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@ -3108,6 +3108,21 @@ static bool str_is_empty(const char *s)
return !s || !s[0];
}
static bool is_flex_arr(const struct btf *btf,
const struct bpf_core_accessor *acc,
const struct btf_array *arr)
{
const struct btf_type *t;
/* not a flexible array, if not inside a struct or has non-zero size */
if (!acc->name || arr->nelems > 0)
return false;
/* has to be the last member of enclosing struct */
t = btf__type_by_id(btf, acc->type_id);
return acc->idx == btf_vlen(t) - 1;
}
/*
* Turn bpf_field_reloc into a low- and high-level spec representation,
* validating correctness along the way, as well as calculating resulting
@ -3145,6 +3160,7 @@ static int bpf_core_spec_parse(const struct btf *btf,
struct bpf_core_spec *spec)
{
int access_idx, parsed_len, i;
struct bpf_core_accessor *acc;
const struct btf_type *t;
const char *name;
__u32 id;
@ -3192,6 +3208,7 @@ static int bpf_core_spec_parse(const struct btf *btf,
return -EINVAL;
access_idx = spec->raw_spec[i];
acc = &spec->spec[spec->len];
if (btf_is_composite(t)) {
const struct btf_member *m;
@ -3209,18 +3226,23 @@ static int bpf_core_spec_parse(const struct btf *btf,
if (str_is_empty(name))
return -EINVAL;
spec->spec[spec->len].type_id = id;
spec->spec[spec->len].idx = access_idx;
spec->spec[spec->len].name = name;
acc->type_id = id;
acc->idx = access_idx;
acc->name = name;
spec->len++;
}
id = m->type;
} else if (btf_is_array(t)) {
const struct btf_array *a = btf_array(t);
bool flex;
t = skip_mods_and_typedefs(btf, a->type, &id);
if (!t || access_idx >= a->nelems)
if (!t)
return -EINVAL;
flex = is_flex_arr(btf, acc - 1, a);
if (!flex && access_idx >= a->nelems)
return -EINVAL;
spec->spec[spec->len].type_id = id;
@ -3525,12 +3547,14 @@ static int bpf_core_spec_match(struct bpf_core_spec *local_spec,
*/
if (i > 0) {
const struct btf_array *a;
bool flex;
if (!btf_is_array(targ_type))
return 0;
a = btf_array(targ_type);
if (local_acc->idx >= a->nelems)
flex = is_flex_arr(targ_btf, targ_acc - 1, a);
if (!flex && local_acc->idx >= a->nelems)
return 0;
if (!skip_mods_and_typedefs(targ_btf, a->type,
&targ_id))