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libbpf: add .BTF.ext offset relocation section loading

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Add support for BPF CO-RE offset relocations. Add section/record
iteration macros for .BTF.ext. These macro are useful for iterating over
each .BTF.ext record, either for dumping out contents or later for BPF
CO-RE relocation handling.

To enable other parts of libbpf to work with .BTF.ext contents, moved
a bunch of type definitions into libbpf_internal.h.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2019-08-07 14:39:50 -07:00 committed by Alexei Starovoitov
parent b03bc6853c
commit 4cedc0dad9
3 changed files with 136 additions and 42 deletions
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69
tools/lib/bpf/btf.c
View File

@ -35,47 +35,6 @@ struct btf {
int fd;
};
struct btf_ext_info {
/*
* info points to the individual info section (e.g. func_info and
* line_info) from the .BTF.ext. It does not include the __u32 rec_size.
*/
void *info;
__u32 rec_size;
__u32 len;
};
struct btf_ext {
union {
struct btf_ext_header *hdr;
void *data;
};
struct btf_ext_info func_info;
struct btf_ext_info line_info;
__u32 data_size;
};
struct btf_ext_info_sec {
__u32 sec_name_off;
__u32 num_info;
/* Followed by num_info * record_size number of bytes */
__u8 data[0];
};
/* The minimum bpf_func_info checked by the loader */
struct bpf_func_info_min {
__u32 insn_off;
__u32 type_id;
};
/* The minimum bpf_line_info checked by the loader */
struct bpf_line_info_min {
__u32 insn_off;
__u32 file_name_off;
__u32 line_off;
__u32 line_col;
};
static inline __u64 ptr_to_u64(const void *ptr)
{
return (__u64) (unsigned long) ptr;
@ -822,6 +781,9 @@ static int btf_ext_setup_info(struct btf_ext *btf_ext,
/* The start of the info sec (including the __u32 record_size). */
void *info;
if (ext_sec->len == 0)
return 0;
if (ext_sec->off & 0x03) {
pr_debug(".BTF.ext %s section is not aligned to 4 bytes\n",
ext_sec->desc);
@ -925,11 +887,24 @@ static int btf_ext_setup_line_info(struct btf_ext *btf_ext)
return btf_ext_setup_info(btf_ext, &param);
}
static int btf_ext_setup_offset_reloc(struct btf_ext *btf_ext)
{
struct btf_ext_sec_setup_param param = {
.off = btf_ext->hdr->offset_reloc_off,
.len = btf_ext->hdr->offset_reloc_len,
.min_rec_size = sizeof(struct bpf_offset_reloc),
.ext_info = &btf_ext->offset_reloc_info,
.desc = "offset_reloc",
};
return btf_ext_setup_info(btf_ext, &param);
}
static int btf_ext_parse_hdr(__u8 *data, __u32 data_size)
{
const struct btf_ext_header *hdr = (struct btf_ext_header *)data;
if (data_size < offsetof(struct btf_ext_header, func_info_off) ||
if (data_size < offsetofend(struct btf_ext_header, hdr_len) ||
data_size < hdr->hdr_len) {
pr_debug("BTF.ext header not found");
return -EINVAL;
@ -987,6 +962,9 @@ struct btf_ext *btf_ext__new(__u8 *data, __u32 size)
}
memcpy(btf_ext->data, data, size);
if (btf_ext->hdr->hdr_len <
offsetofend(struct btf_ext_header, line_info_len))
goto done;
err = btf_ext_setup_func_info(btf_ext);
if (err)
goto done;
@ -995,6 +973,13 @@ struct btf_ext *btf_ext__new(__u8 *data, __u32 size)
if (err)
goto done;
if (btf_ext->hdr->hdr_len <
offsetofend(struct btf_ext_header, offset_reloc_len))
goto done;
err = btf_ext_setup_offset_reloc(btf_ext);
if (err)
goto done;
done:
if (err) {
btf_ext__free(btf_ext);

4
tools/lib/bpf/btf.h
View File

@ -58,6 +58,10 @@ struct btf_ext_header {
__u32 func_info_len;
__u32 line_info_off;
__u32 line_info_len;
/* optional part of .BTF.ext header */
__u32 offset_reloc_off;
__u32 offset_reloc_len;
};
LIBBPF_API void btf__free(struct btf *btf);

105
tools/lib/bpf/libbpf_internal.h
View File

@ -29,6 +29,10 @@
#ifndef max
# define max(x, y) ((x) < (y) ? (y) : (x))
#endif
#ifndef offsetofend
# define offsetofend(TYPE, FIELD) \
(offsetof(TYPE, FIELD) + sizeof(((TYPE *)0)->FIELD))
#endif
extern void libbpf_print(enum libbpf_print_level level,
const char *format, ...)
@ -46,4 +50,105 @@ do { \
int libbpf__load_raw_btf(const char *raw_types, size_t types_len,
const char *str_sec, size_t str_len);
struct btf_ext_info {
/*
* info points to the individual info section (e.g. func_info and
* line_info) from the .BTF.ext. It does not include the __u32 rec_size.
*/
void *info;
__u32 rec_size;
__u32 len;
};
#define for_each_btf_ext_sec(seg, sec) \
for (sec = (seg)->info; \
(void *)sec < (seg)->info + (seg)->len; \
sec = (void *)sec + sizeof(struct btf_ext_info_sec) + \
(seg)->rec_size * sec->num_info)
#define for_each_btf_ext_rec(seg, sec, i, rec) \
for (i = 0, rec = (void *)&(sec)->data; \
i < (sec)->num_info; \
i++, rec = (void *)rec + (seg)->rec_size)
struct btf_ext {
union {
struct btf_ext_header *hdr;
void *data;
};
struct btf_ext_info func_info;
struct btf_ext_info line_info;
struct btf_ext_info offset_reloc_info;
__u32 data_size;
};
struct btf_ext_info_sec {
__u32 sec_name_off;
__u32 num_info;
/* Followed by num_info * record_size number of bytes */
__u8 data[0];
};
/* The minimum bpf_func_info checked by the loader */
struct bpf_func_info_min {
__u32 insn_off;
__u32 type_id;
};
/* The minimum bpf_line_info checked by the loader */
struct bpf_line_info_min {
__u32 insn_off;
__u32 file_name_off;
__u32 line_off;
__u32 line_col;
};
/* The minimum bpf_offset_reloc checked by the loader
*
* Offset relocation captures the following data:
* - insn_off - instruction offset (in bytes) within a BPF program that needs
* its insn->imm field to be relocated with actual offset;
* - type_id - BTF type ID of the "root" (containing) entity of a relocatable
* offset;
* - access_str_off - offset into corresponding .BTF string section. String
* itself encodes an accessed field using a sequence of field and array
* indicies, separated by colon (:). It's conceptually very close to LLVM's
* getelementptr ([0]) instruction's arguments for identifying offset to
* a field.
*
* Example to provide a better feel.
*
* struct sample {
* int a;
* struct {
* int b[10];
* };
* };
*
* struct sample *s = ...;
* int x = &s->a; // encoded as "0:0" (a is field #0)
* int y = &s->b[5]; // encoded as "0:1:0:5" (anon struct is field #1,
* // b is field #0 inside anon struct, accessing elem #5)
* int z = &s[10]->b; // encoded as "10:1" (ptr is used as an array)
*
* type_id for all relocs in this example will capture BTF type id of
* `struct sample`.
*
* Such relocation is emitted when using __builtin_preserve_access_index()
* Clang built-in, passing expression that captures field address, e.g.:
*
* bpf_probe_read(&dst, sizeof(dst),
* __builtin_preserve_access_index(&src->a.b.c));
*
* In this case Clang will emit offset relocation recording necessary data to
* be able to find offset of embedded `a.b.c` field within `src` struct.
*
* [0] https://llvm.org/docs/LangRef.html#getelementptr-instruction
*/
struct bpf_offset_reloc {
__u32 insn_off;
__u32 type_id;
__u32 access_str_off;
};
#endif /* __LIBBPF_LIBBPF_INTERNAL_H */