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libbpf: Add internal helper to load BTF data by FD 

Add a btf_get_from_fd() helper, which constructs struct btf from in-kernel BTF
data by FD. This is used for loading module BTFs.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201203204634.1325171-4-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2020-12-03 12:46:23 -08:00 committed by Alexei Starovoitov
parent 2fe8890848
commit a19f93cfaf
2 changed files with 36 additions and 26 deletions
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61
tools/lib/bpf/btf.c
View File

@ -1323,35 +1323,27 @@ const char *btf__name_by_offset(const struct btf *btf, __u32 offset)
return btf__str_by_offset(btf, offset); return btf__str_by_offset(btf, offset);
} }
int btf__get_from_id(__u32 id, struct btf **btf) struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
{ {
struct bpf_btf_info btf_info = { 0 }; struct bpf_btf_info btf_info;
__u32 len = sizeof(btf_info); __u32 len = sizeof(btf_info);
__u32 last_size; __u32 last_size;
int btf_fd; struct btf *btf;
void *ptr; void *ptr;
int err; int err;
err = 0;
*btf = NULL;
btf_fd = bpf_btf_get_fd_by_id(id);
if (btf_fd < 0)
return 0;
/* we won't know btf_size until we call bpf_obj_get_info_by_fd(). so /* we won't know btf_size until we call bpf_obj_get_info_by_fd(). so
* let's start with a sane default - 4KiB here - and resize it only if * let's start with a sane default - 4KiB here - and resize it only if
* bpf_obj_get_info_by_fd() needs a bigger buffer. * bpf_obj_get_info_by_fd() needs a bigger buffer.
*/ */
btf_info.btf_size = 4096; last_size = 4096;
last_size = btf_info.btf_size;
ptr = malloc(last_size); ptr = malloc(last_size);
if (!ptr) { if (!ptr)
err = -ENOMEM; return ERR_PTR(-ENOMEM);
goto exit_free;
}
memset(ptr, 0, last_size); memset(&btf_info, 0, sizeof(btf_info));
btf_info.btf = ptr_to_u64(ptr); btf_info.btf = ptr_to_u64(ptr);
btf_info.btf_size = last_size;
err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len); err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len);
if (!err && btf_info.btf_size > last_size) { if (!err && btf_info.btf_size > last_size) {
@ -1360,31 +1352,48 @@ int btf__get_from_id(__u32 id, struct btf **btf)
last_size = btf_info.btf_size; last_size = btf_info.btf_size;
temp_ptr = realloc(ptr, last_size); temp_ptr = realloc(ptr, last_size);
if (!temp_ptr) { if (!temp_ptr) {
err = -ENOMEM; btf = ERR_PTR(-ENOMEM);
goto exit_free; goto exit_free;
} }
ptr = temp_ptr; ptr = temp_ptr;
memset(ptr, 0, last_size);
len = sizeof(btf_info);
memset(&btf_info, 0, sizeof(btf_info));
btf_info.btf = ptr_to_u64(ptr); btf_info.btf = ptr_to_u64(ptr);
btf_info.btf_size = last_size;
err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len); err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len);
} }
if (err || btf_info.btf_size > last_size) { if (err || btf_info.btf_size > last_size) {
err = errno; btf = err ? ERR_PTR(-errno) : ERR_PTR(-E2BIG);
goto exit_free; goto exit_free;
} }
*btf = btf__new((__u8 *)(long)btf_info.btf, btf_info.btf_size); btf = btf_new(ptr, btf_info.btf_size, base_btf);
if (IS_ERR(*btf)) {
err = PTR_ERR(*btf);
*btf = NULL;
}
exit_free: exit_free:
close(btf_fd);
free(ptr); free(ptr);
return btf;
}
return err; int btf__get_from_id(__u32 id, struct btf **btf)
{
struct btf *res;
int btf_fd;
*btf = NULL;
btf_fd = bpf_btf_get_fd_by_id(id);
if (btf_fd < 0)
return -errno;
res = btf_get_from_fd(btf_fd, NULL);
close(btf_fd);
if (IS_ERR(res))
return PTR_ERR(res);
*btf = res;
return 0;
} }
int btf__get_map_kv_tids(const struct btf *btf, const char *map_name, int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,

1
tools/lib/bpf/libbpf_internal.h
View File

@ -155,6 +155,7 @@ int bpf_object__section_size(const struct bpf_object *obj, const char *name,
__u32 *size); __u32 *size);
int bpf_object__variable_offset(const struct bpf_object *obj, const char *name, int bpf_object__variable_offset(const struct bpf_object *obj, const char *name,
__u32 *off); __u32 *off);
struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf);
struct btf_ext_info { struct btf_ext_info {
/* /*