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dlfcn-util: add static asserts ensuring our sym_xyz() func ptrs match the types from the official headers

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Make sure that the sym_xyz function pointers have the types that the
functions we'll assign them have.

And of course, this found a number of incompatibilities right-away, in
particular in the bpf hookup.

(Doing this will trigger deprecation warnings from libbpf. I simply
turned them off locally now, since we are well aware of what we are
doing in that regard.)

There's one return type fix (bool → int), that actually matters I think,
as it might have created an incompatibility on some archs.
This commit is contained in:
Lennart Poettering 2022-11-16 21:37:20 +01:00
parent 28795f2c13
commit 7736a71fd2
7 changed files with 64 additions and 12 deletions
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2
src/shared/bpf-compat.h
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@ -25,7 +25,7 @@ struct bpf_map_create_opts;
* - before the compat static inline helpers that use them.
* When removing this file move these back to bpf-dlopen.h */
extern int (*sym_bpf_map_create)(enum bpf_map_type, const char *, __u32, __u32, __u32, const struct bpf_map_create_opts *);
extern bool (*sym_libbpf_probe_bpf_prog_type)(enum bpf_prog_type, const void *);
extern int (*sym_libbpf_probe_bpf_prog_type)(enum bpf_prog_type, const void *);
/* compat symbols removed in libbpf 1.0 */
extern int (*sym_bpf_create_map)(enum bpf_map_type, int key_size, int value_size, int max_entries, __u32 map_flags);

50
src/shared/bpf-dlopen.c
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@ -6,8 +6,20 @@
#include "strv.h"
#if HAVE_LIBBPF
struct bpf_link* (*sym_bpf_program__attach_cgroup)(struct bpf_program *, int);
struct bpf_link* (*sym_bpf_program__attach_lsm)(struct bpf_program *);
/* 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
struct bpf_link* (*sym_bpf_program__attach_cgroup)(const struct bpf_program *, int);
struct bpf_link* (*sym_bpf_program__attach_lsm)(const struct bpf_program *);
int (*sym_bpf_link__fd)(const struct bpf_link *);
int (*sym_bpf_link__destroy)(struct bpf_link *);
int (*sym_bpf_map__fd)(const struct bpf_map *);
@ -22,7 +34,7 @@ int (*sym_bpf_object__load_skeleton)(struct bpf_object_skeleton *);
int (*sym_bpf_object__attach_skeleton)(struct bpf_object_skeleton *);
void (*sym_bpf_object__detach_skeleton)(struct bpf_object_skeleton *);
void (*sym_bpf_object__destroy_skeleton)(struct bpf_object_skeleton *);
bool (*sym_libbpf_probe_bpf_prog_type)(enum bpf_prog_type, const void *);
int (*sym_libbpf_probe_bpf_prog_type)(enum bpf_prog_type, const void *);
const char* (*sym_bpf_program__name)(const struct bpf_program *);
libbpf_print_fn_t (*sym_libbpf_set_print)(libbpf_print_fn_t);
long (*sym_libbpf_get_error)(const void *);
@ -49,6 +61,8 @@ int dlopen_bpf(void) {
void *dl;
int r;
DISABLE_WARNING_DEPRECATED_DECLARATIONS;
dl = dlopen("libbpf.so.1", RTLD_LAZY);
if (!dl) {
/* libbpf < 1.0.0 (we rely on 0.1.0+) provide most symbols we care about, but
@ -61,14 +75,29 @@ int dlopen_bpf(void) {
"neither libbpf.so.1 nor libbpf.so.0 are installed: %s", dlerror());
/* symbols deprecated in 1.0 we use as compat */
r = dlsym_many_or_warn(dl, LOG_DEBUG,
r = dlsym_many_or_warn(
dl, LOG_DEBUG,
#if MODERN_LIBBPF
/* Don't exist anymore in new libbpf, hence cannot type check them */
DLSYM_ARG_FORCE(bpf_create_map),
DLSYM_ARG_FORCE(bpf_probe_prog_type));
#else
DLSYM_ARG(bpf_create_map),
DLSYM_ARG(bpf_probe_prog_type));
#endif
} else {
/* symbols available from 0.7.0 */
r = dlsym_many_or_warn(dl, LOG_DEBUG,
r = dlsym_many_or_warn(
dl, LOG_DEBUG,
#if MODERN_LIBBPF
DLSYM_ARG(bpf_map_create),
DLSYM_ARG(libbpf_probe_bpf_prog_type));
DLSYM_ARG(libbpf_probe_bpf_prog_type)
#else
/* These symbols did not exist in old libbpf, hence we cannot type check them */
DLSYM_ARG_FORCE(bpf_map_create),
DLSYM_ARG_FORCE(libbpf_probe_bpf_prog_type)
#endif
);
}
r = dlsym_many_or_warn(
@ -86,8 +115,14 @@ int dlopen_bpf(void) {
DLSYM_ARG(bpf_object__attach_skeleton),
DLSYM_ARG(bpf_object__detach_skeleton),
DLSYM_ARG(bpf_object__destroy_skeleton),
#if MODERN_LIBBPF
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_cgroup),
DLSYM_ARG_FORCE(bpf_program__attach_lsm),
#endif
DLSYM_ARG(bpf_program__name),
DLSYM_ARG(libbpf_set_print),
DLSYM_ARG(libbpf_get_error));
@ -96,6 +131,9 @@ int dlopen_bpf(void) {
/* We set the print helper unconditionally. Otherwise libbpf will emit not useful log messages. */
(void) sym_libbpf_set_print(bpf_print_func);
REENABLE_WARNING;
return r;
}

4
src/shared/bpf-dlopen.h
View File

@ -8,8 +8,8 @@
#include "bpf-compat.h"
extern struct bpf_link* (*sym_bpf_program__attach_cgroup)(struct bpf_program *, int);
extern struct bpf_link* (*sym_bpf_program__attach_lsm)(struct bpf_program *);
extern struct bpf_link* (*sym_bpf_program__attach_cgroup)(const struct bpf_program *, int);
extern struct bpf_link* (*sym_bpf_program__attach_lsm)(const struct bpf_program *);
extern int (*sym_bpf_link__fd)(const struct bpf_link *);
extern int (*sym_bpf_link__destroy)(struct bpf_link *);
extern int (*sym_bpf_map__fd)(const struct bpf_map *);

10
src/shared/cryptsetup-util.c
View File

@ -205,6 +205,14 @@ int dlopen_cryptsetup(void) {
#if HAVE_LIBCRYPTSETUP
int r;
/* libcryptsetup added crypt_reencrypt() in 2.2.0, and marked it obsolete in 2.4.0, replacing it with
* crypt_reencrypt_run(), which takes one extra argument but is otherwise identical. The old call is
* still available though, and given we want to support 2.2.0 for a while longer, we'll stick to the
* old symbol. Howerver, the old symbols now has a GCC deprecation decorator, hence let's turn off
* warnings about this for now. */
DISABLE_WARNING_DEPRECATED_DECLARATIONS;
r = dlopen_many_sym_or_warn(
&cryptsetup_dl, "libcryptsetup.so.12", LOG_DEBUG,
DLSYM_ARG(crypt_activate_by_passphrase),
@ -262,6 +270,8 @@ int dlopen_cryptsetup(void) {
if (r <= 0)
return r;
REENABLE_WARNING;
/* Redirect the default logging calls of libcryptsetup to our own logging infra. (Note that
* libcryptsetup also maintains per-"struct crypt_device" log functions, which we'll also set
* whenever allocating a "struct crypt_device" context. Why set both? To be defensive: maybe some

4
src/shared/dlfcn-util.h
View File

@ -19,4 +19,8 @@ int dlopen_many_sym_or_warn_sentinel(void **dlp, const char *filename, int log_l
* that each library symbol to resolve will be placed in a variable with the "sym_" prefix, i.e. a symbol
* "foobar" is loaded into a variable "sym_foobar". */
#define DLSYM_ARG(arg) \
({ assert_cc(__builtin_types_compatible_p(typeof(sym_##arg), typeof(&arg))); &sym_##arg; }), STRINGIFY(arg)
/* libbpf is a bit confused about type-safety and API compatibility. Provide a macro that can tape over that mess. Sad. */
#define DLSYM_ARG_FORCE(arg) \
&sym_##arg, STRINGIFY(arg)

4
src/shared/idn-util.c
View File

@ -17,7 +17,7 @@ static void* idn_dl = NULL;
#if HAVE_LIBIDN2
int (*sym_idn2_lookup_u8)(const uint8_t* src, uint8_t** lookupname, int flags) = NULL;
const char *(*sym_idn2_strerror)(int rc) = NULL;
const char *(*sym_idn2_strerror)(int rc) _const_ = NULL;
int (*sym_idn2_to_unicode_8z8z)(const char * input, char ** output, int flags) = NULL;
int dlopen_idn(void) {
@ -31,7 +31,7 @@ int dlopen_idn(void) {
#if HAVE_LIBIDN
int (*sym_idna_to_ascii_4i)(const uint32_t * in, size_t inlen, char *out, int flags);
int (*sym_idna_to_unicode_44i)(const uint32_t * in, size_t inlen,uint32_t * out, size_t * outlen, int flags);
int (*sym_idna_to_unicode_44i)(const uint32_t * in, size_t inlen, uint32_t * out, size_t * outlen, int flags);
char* (*sym_stringprep_ucs4_to_utf8)(const uint32_t * str, ssize_t len, size_t * items_read, size_t * items_written);
uint32_t* (*sym_stringprep_utf8_to_ucs4)(const char *str, ssize_t len, size_t *items_written);

2
src/shared/idn-util.h
View File

@ -20,7 +20,7 @@ static inline int dlopen_idn(void) {
#if HAVE_LIBIDN2
extern int (*sym_idn2_lookup_u8)(const uint8_t* src, uint8_t** lookupname, int flags);
extern const char *(*sym_idn2_strerror)(int rc);
extern const char *(*sym_idn2_strerror)(int rc) _const_;
extern int (*sym_idn2_to_unicode_8z8z)(const char * input, char ** output, int flags);
#endif