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systemd/src/shared/bpf-util.c
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Luca Boccassi 590e226437 shared: add DLOPEN_* wrapper macros that stamp .note.dlopen on callers 
This macro emits an SD_ELF_NOTE_DLOPEN note so that calling sites,
and not just libsystemd-shared, get the ELF stamped with the notes
documenting the dependency. Currently most of the dlopen notes end
up in libsystemd-shared, and executables have no way to document
the optional dependencies they need. With this new macro, this
issue can be fixed.

Co-developed-by: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-01 18:24:15 +01:00

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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include "sd-dlopen.h"
#include "bpf-util.h"
#include "dlfcn-util.h"
#include "initrd-util.h"
#include "log.h"
#include "strv.h"
#if HAVE_LIBBPF
/* libbpf changed types of function prototypes around, so we need to disable some type checking for older
* libbpf. We consider everything older than 0.7 too old for accurate type checks. */
#if defined(__LIBBPF_CURRENT_VERSION_GEQ)
#if __LIBBPF_CURRENT_VERSION_GEQ(0, 7)
#define MODERN_LIBBPF 1
#endif
#endif
#if !defined(MODERN_LIBBPF)
#define MODERN_LIBBPF 0
#endif
static DLSYM_PROTOTYPE(libbpf_get_error) = NULL;
DLSYM_PROTOTYPE(bpf_create_map) = NULL;
DLSYM_PROTOTYPE(bpf_link__destroy) = NULL;
DLSYM_PROTOTYPE(bpf_link__fd) = NULL;
DLSYM_PROTOTYPE(bpf_link__open) = NULL;
DLSYM_PROTOTYPE(bpf_link__pin) = NULL;
DLSYM_PROTOTYPE(bpf_map__fd) = NULL;
DLSYM_PROTOTYPE(bpf_map__name) = NULL;
DLSYM_PROTOTYPE(bpf_map__set_inner_map_fd) = NULL;
DLSYM_PROTOTYPE(bpf_map__set_max_entries) = NULL;
DLSYM_PROTOTYPE(bpf_map__set_pin_path) = NULL;
DLSYM_PROTOTYPE(bpf_map_create) = NULL;
DLSYM_PROTOTYPE(bpf_map_delete_elem) = NULL;
DLSYM_PROTOTYPE(bpf_map_get_fd_by_id) = NULL;
DLSYM_PROTOTYPE(bpf_map_lookup_elem) = NULL;
DLSYM_PROTOTYPE(bpf_map_update_elem) = NULL;
DLSYM_PROTOTYPE(bpf_obj_get_info_by_fd) = NULL;
DLSYM_PROTOTYPE(bpf_object__attach_skeleton) = NULL;
DLSYM_PROTOTYPE(bpf_object__destroy_skeleton) = NULL;
DLSYM_PROTOTYPE(bpf_object__detach_skeleton) = NULL;
DLSYM_PROTOTYPE(bpf_object__load_skeleton) = NULL;
DLSYM_PROTOTYPE(bpf_object__name) = NULL;
DLSYM_PROTOTYPE(bpf_object__next_map) = NULL;
DLSYM_PROTOTYPE(bpf_object__open_skeleton) = NULL;
DLSYM_PROTOTYPE(bpf_object__pin_maps) = NULL;
DLSYM_PROTOTYPE(bpf_program__attach) = NULL;
DLSYM_PROTOTYPE(bpf_program__attach_cgroup) = NULL;
DLSYM_PROTOTYPE(bpf_program__attach_lsm) = NULL;
DLSYM_PROTOTYPE(bpf_program__name) = NULL;
DLSYM_PROTOTYPE(bpf_program__set_autoload) = NULL;
static int missing_bpf_token_create(int bpffs_fd, struct bpf_token_create_opts *opts) {
return -ENOSYS;
}
DLSYM_PROTOTYPE(bpf_token_create) = missing_bpf_token_create;
DLSYM_PROTOTYPE(libbpf_set_print) = NULL;
DLSYM_PROTOTYPE(ring_buffer__epoll_fd) = NULL;
DLSYM_PROTOTYPE(ring_buffer__free) = NULL;
DLSYM_PROTOTYPE(ring_buffer__new) = NULL;
DLSYM_PROTOTYPE(ring_buffer__poll) = NULL;
_printf_(2,0)
static int bpf_print_func(enum libbpf_print_level level, const char *fmt, va_list ap) {
#if !LOG_TRACE
/* libbpf logs a lot of details at its debug level, which we don't need to see. */
if (level == LIBBPF_DEBUG)
return 0;
#endif
/* All other levels are downgraded to LOG_DEBUG */
/* errno is used here, on the assumption that if the log message uses %m, errno will be set to
* something useful. Otherwise, it shouldn't matter, we may pass 0 or some bogus value. */
return log_internalv(LOG_DEBUG, errno, NULL, 0, NULL, fmt, ap);
}
int dlopen_bpf(int log_level) {
static void *bpf_dl = NULL;
static int cached = 0;
int r = -ENOENT;
if (bpf_dl)
return 1; /* Already loaded */
if (cached < 0)
return cached; /* Already tried, and failed. */
BPF_NOTE(SD_ELF_NOTE_DLOPEN_PRIORITY_SUGGESTED);
DISABLE_WARNING_DEPRECATED_DECLARATIONS;
FOREACH_STRING(soname, "libbpf.so.1", "libbpf.so.0") {
r = dlopen_many_sym_or_warn(
&bpf_dl, soname, LOG_DEBUG,
DLSYM_ARG(bpf_link__destroy),
DLSYM_ARG(bpf_link__fd),
DLSYM_ARG(bpf_link__open),
DLSYM_ARG(bpf_link__pin),
DLSYM_ARG(bpf_map__fd),
DLSYM_ARG(bpf_map__name),
DLSYM_ARG(bpf_map__set_inner_map_fd),
DLSYM_ARG(bpf_map__set_max_entries),
DLSYM_ARG(bpf_map__set_pin_path),
DLSYM_ARG(bpf_map_delete_elem),
DLSYM_ARG(bpf_map_get_fd_by_id),
DLSYM_ARG(bpf_map_lookup_elem),
DLSYM_ARG(bpf_map_update_elem),
DLSYM_ARG(bpf_obj_get_info_by_fd),
DLSYM_ARG(bpf_object__attach_skeleton),
DLSYM_ARG(bpf_object__destroy_skeleton),
DLSYM_ARG(bpf_object__detach_skeleton),
DLSYM_ARG(bpf_object__load_skeleton),
DLSYM_ARG(bpf_object__name),
DLSYM_ARG(bpf_object__open_skeleton),
DLSYM_ARG(bpf_object__pin_maps),
#if MODERN_LIBBPF
DLSYM_ARG(bpf_program__attach),
DLSYM_ARG(bpf_program__attach_cgroup),
DLSYM_ARG(bpf_program__attach_lsm),
#else
/* libbpf added a "const" to function parameters where it should not have, ignore this type incompatibility */
DLSYM_ARG_FORCE(bpf_program__attach),
DLSYM_ARG_FORCE(bpf_program__attach_cgroup),
DLSYM_ARG_FORCE(bpf_program__attach_lsm),
#endif
DLSYM_ARG(bpf_program__name),
DLSYM_ARG(bpf_program__set_autoload),
DLSYM_ARG(libbpf_get_error),
DLSYM_ARG(libbpf_set_print),
DLSYM_ARG(ring_buffer__epoll_fd),
DLSYM_ARG(ring_buffer__free),
DLSYM_ARG(ring_buffer__new),
DLSYM_ARG(ring_buffer__poll));
if (r >= 0)
break;
}
REENABLE_WARNING;
if (r < 0)
return cached = log_full_errno(in_initrd() ? LOG_DEBUG : log_level, r,
"Neither libbpf.so.1 nor libbpf.so.0 are installed, cgroup BPF features disabled.");
/* Version-specific symbols: bpf_create_map exists only in libbpf < 1.0; bpf_map_create and
* bpf_object__next_map only in 0.7+. bpf_token_create only in 1.5+. Unresolved prototypes keep
* their initializers (NULL, or a fallback returning -ENOSYS for bpf_token_create). */
DLSYM_OPTIONAL(bpf_dl, bpf_create_map);
DLSYM_OPTIONAL(bpf_dl, bpf_map_create);
DLSYM_OPTIONAL(bpf_dl, bpf_object__next_map);
DLSYM_OPTIONAL(bpf_dl, bpf_token_create);
/* We set the print helper unconditionally. Otherwise libbpf will emit not useful log messages. */
(void) sym_libbpf_set_print(bpf_print_func);
return 1;
}
int bpf_get_error_translated(const void *ptr) {
int r;
r = sym_libbpf_get_error(ptr);
switch (r) {
case -524:
/* Workaround for kernel bug, BPF returns an internal error instead of translating it, until
* it is fixed:
* https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/errno.h?h=v6.9&id=a38297e3fb012ddfa7ce0321a7e5a8daeb1872b6#n27
*/
return -EOPNOTSUPP;
default:
return r;
}
}
#else
int dlopen_bpf(int log_level) {
return log_once_errno(log_level, SYNTHETIC_ERRNO(EOPNOTSUPP),
"libbpf support is not compiled in, cgroup BPF features disabled.");
}
#endif
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