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libbpf: Add support for field size relocations

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Add bpf_core_field_size() macro, capturing a relocation against field size.
Adjust bits of internal libbpf relocation logic to allow capturing size
relocations of various field types: arrays, structs/unions, enums, etc.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20191101222810.1246166-4-andriin@fb.com
This commit is contained in:
Andrii Nakryiko 2019-11-01 15:28:08 -07:00 committed by Andrii Nakryiko
parent 4438972ccc
commit df45cf7a3e
2 changed files with 39 additions and 8 deletions
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7
src/bpf_core_read.h
View File

@ -96,6 +96,13 @@ enum bpf_field_info_kind {
#define bpf_core_field_exists(field) \
__builtin_preserve_field_info(field, BPF_FIELD_EXISTS)
/*
* Convenience macro to get byte size of a field. Works for integers,
* struct/unions, pointers, arrays, and enums.
*/
#define bpf_core_field_size(field) \
__builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE)
/*
* bpf_core_read() abstracts away bpf_probe_read() call and captures offset
* relocation for source address using __builtin_preserve_access_index()

40
src/libbpf.c
View File

@ -2704,8 +2704,10 @@ err_out:
/* Check two types for compatibility, skipping const/volatile/restrict and
* typedefs, to ensure we are relocating compatible entities:
* - any two STRUCTs/UNIONs are compatible and can be mixed;
* - any two FWDs are compatible;
* - any two FWDs are compatible, if their names match (modulo flavor suffix);
* - any two PTRs are always compatible;
* - for ENUMs, names should be the same (ignoring flavor suffix) or at
* least one of enums should be anonymous;
* - for ENUMs, check sizes, names are ignored;
* - for INT, size and signedness are ignored;
* - for ARRAY, dimensionality is ignored, element types are checked for
@ -2733,11 +2735,23 @@ recur:
return 0;
switch (btf_kind(local_type)) {
case BTF_KIND_FWD:
case BTF_KIND_PTR:
return 1;
case BTF_KIND_ENUM:
return local_type->size == targ_type->size;
case BTF_KIND_FWD:
case BTF_KIND_ENUM: {
const char *local_name, *targ_name;
size_t local_len, targ_len;
local_name = btf__name_by_offset(local_btf,
local_type->name_off);
targ_name = btf__name_by_offset(targ_btf, targ_type->name_off);
local_len = bpf_core_essential_name_len(local_name);
targ_len = bpf_core_essential_name_len(targ_name);
/* one of them is anonymous or both w/ same flavor-less names */
return local_len == 0 || targ_len == 0 ||
(local_len == targ_len &&
strncmp(local_name, targ_name, local_len) == 0);
}
case BTF_KIND_INT:
/* just reject deprecated bitfield-like integers; all other
* integers are by default compatible between each other
@ -2926,16 +2940,23 @@ static int bpf_core_calc_field_relo(const struct bpf_program *prog,
const struct btf_member *m;
const struct btf_type *mt;
bool bitfield;
__s64 sz;
/* a[n] accessor needs special handling */
if (!acc->name) {
if (relo->kind != BPF_FIELD_BYTE_OFFSET) {
pr_warn("prog '%s': relo %d at insn #%d can't be applied to array access'\n",
if (relo->kind == BPF_FIELD_BYTE_OFFSET) {
*val = spec->bit_offset / 8;
} else if (relo->kind == BPF_FIELD_BYTE_SIZE) {
sz = btf__resolve_size(spec->btf, acc->type_id);
if (sz < 0)
return -EINVAL;
*val = sz;
} else {
pr_warn("prog '%s': relo %d at insn #%d can't be applied to array access\n",
bpf_program__title(prog, false),
relo->kind, relo->insn_off / 8);
return -EINVAL;
}
*val = spec->bit_offset / 8;
if (validate)
*validate = true;
return 0;
@ -2963,7 +2984,10 @@ static int bpf_core_calc_field_relo(const struct bpf_program *prog,
byte_off = bit_off / 8 / byte_sz * byte_sz;
}
} else {
byte_sz = mt->size;
sz = btf__resolve_size(spec->btf, m->type);
if (sz < 0)
return -EINVAL;
byte_sz = sz;
byte_off = spec->bit_offset / 8;
bit_sz = byte_sz * 8;
}