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BTF-playground: Cannot get kernel BTF obj ID this way

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Signed-off-by: Jesper Dangaard Brouer <netoptimizer@brouer.com>
This commit is contained in:
Jesper Dangaard Brouer
2022-08-30 19:16:41 +02:00
parent ee0ed78ce8
commit f0755442ff
1 changed files with 38 additions and 2 deletions
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40
BTF-playground/btf_module_read.c
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@@ -11,6 +11,7 @@
#include <unistd.h>
#include <getopt.h>
#include <bpf/bpf.h>
#include <bpf/btf.h> /* Notice libbpf BTF include */
#include <linux/err.h>
@@ -32,11 +33,42 @@ int print_all_levels(enum libbpf_print_level level,
#define pr_err(fmt, ...) \
fprintf(stderr, "%s:%d - " fmt, __FILE__, __LINE__, ##__VA_ARGS__)
int fail1_get_kernel_btf_obj_id(struct btf *btf_obj)
{
/* *** DOES NOT WORK ***
*
* The struct btf returned from btf__load_module_btf() doesn't keep the
* file descriptor open. Thus, we never reach bpf_obj_get_info_by_fd().
*
*/
struct bpf_btf_info info;
__u32 len = sizeof(info);
int btf_fd;
int err;
memset(&info, 0, sizeof(info));
btf_fd = btf__fd(btf_obj);
if (btf_fd < 0) {
printf("ERR: No FD(%d) in btf_obj:%p\n", btf_fd, btf_obj);
return 0;
}
err = bpf_obj_get_info_by_fd(btf_fd, &info, &len); /* Privileged op */
if (err) {
printf("ERR(%d): Can't get BTF object info on FD(%d): %s\n",
errno, btf_fd, strerror(errno));
return 0;
}
return info.id;
}
int main(int argc, char **argv)
{
struct btf *vmlinux_btf, *module_btf = NULL;
int opt, longindex = 0;
__u32 btf_obj_id;
__s32 type_id;
int err = 0;
@@ -78,8 +110,12 @@ int main(int argc, char **argv)
goto out;
}
printf("Module:%s Symbol:%s have BTF id:%d\n",
module_name, symbol_name, type_id);
/* Wanted to get BTF object ID used by kernel that ident BTF */
//btf_obj_id = fail1_get_kernel_btf_obj_id(vmlinux_btf);
btf_obj_id = fail1_get_kernel_btf_obj_id(module_btf);
printf("Module:%s (BTF-obj ID:%d) Symbol:%s have BTF type id:%d\n",
module_name, btf_obj_id, symbol_name, type_id);
out:
btf__free(module_btf);