mirror of
https://github.com/morgan9e/systemd
synced 2026-04-14 08:25:20 +09:00
5c672e90a6
When looking at how dlopen for various libs is implemented, I found that the macros hide too much. I find it much easier to see what is going on if 'extern' and '= NULL' are written explicitly. After all, we don't hide those for other definitions, e.g. our style guide says that static variables should be initialized with '= NULL'. With that change, it's much more obvious what is a variable declaration and what is a variable initialization.
81 lines
4.2 KiB
C
81 lines
4.2 KiB
C
/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#pragma once
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#include <dlfcn.h>
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#include "macro.h"
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static inline void* safe_dlclose(void *dl) {
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if (!dl)
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return NULL;
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assert_se(dlclose(dl) == 0);
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return NULL;
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}
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static inline void dlclosep(void **dlp) {
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safe_dlclose(*dlp);
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}
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int dlsym_many_or_warn_sentinel(void *dl, int log_level, ...) _sentinel_;
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int dlopen_many_sym_or_warn_sentinel(void **dlp, const char *filename, int log_level, ...) _sentinel_;
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#define dlsym_many_or_warn(dl, log_level, ...) \
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dlsym_many_or_warn_sentinel(dl, log_level, __VA_ARGS__, NULL)
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#define dlopen_many_sym_or_warn(dlp, filename, log_level, ...) \
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dlopen_many_sym_or_warn_sentinel(dlp, filename, log_level, __VA_ARGS__, NULL)
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#define DLSYM_PROTOTYPE(symbol) \
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typeof(symbol)* sym_##symbol
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/* Macro useful for putting together variable/symbol name pairs when calling dlsym_many_or_warn(). Assumes
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* that each library symbol to resolve will be placed in a variable with the "sym_" prefix, i.e. a symbol
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* "foobar" is loaded into a variable "sym_foobar". */
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#define DLSYM_ARG(arg) \
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({ assert_cc(__builtin_types_compatible_p(typeof(sym_##arg), typeof(&arg))); &sym_##arg; }), STRINGIFY(arg)
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/* libbpf is a bit confused about type-safety and API compatibility. Provide a macro that can tape over that mess. Sad. */
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#define DLSYM_ARG_FORCE(arg) \
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&sym_##arg, STRINGIFY(arg)
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#define ELF_NOTE_DLOPEN_VENDOR "FDO"
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#define ELF_NOTE_DLOPEN_TYPE UINT32_C(0x407c0c0a)
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#define ELF_NOTE_DLOPEN_PRIORITY_REQUIRED "required"
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#define ELF_NOTE_DLOPEN_PRIORITY_RECOMMENDED "recommended"
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#define ELF_NOTE_DLOPEN_PRIORITY_SUGGESTED "suggested"
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/* Add an ".note.dlopen" ELF note to our binary that declares our weak dlopen() dependency. This
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* information can be read from an ELF file via "readelf -p .note.dlopen" or an equivalent command. */
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#define _ELF_NOTE_DLOPEN(json, variable_name) \
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__attribute__((used, section(".note.dlopen"))) _Alignas(sizeof(uint32_t)) static const struct { \
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struct { \
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uint32_t n_namesz, n_descsz, n_type; \
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} nhdr; \
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char name[sizeof(ELF_NOTE_DLOPEN_VENDOR)]; \
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_Alignas(sizeof(uint32_t)) char dlopen_json[sizeof(json)]; \
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} variable_name = { \
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.nhdr = { \
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.n_namesz = sizeof(ELF_NOTE_DLOPEN_VENDOR), \
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.n_descsz = sizeof(json), \
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.n_type = ELF_NOTE_DLOPEN_TYPE, \
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}, \
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.name = ELF_NOTE_DLOPEN_VENDOR, \
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.dlopen_json = json, \
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}
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#define _SONAME_ARRAY1(a) "[\""a"\"]"
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#define _SONAME_ARRAY2(a, b) "[\""a"\",\""b"\"]"
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#define _SONAME_ARRAY3(a, b, c) "[\""a"\",\""b"\",\""c"\"]"
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#define _SONAME_ARRAY4(a, b, c, d) "[\""a"\",\""b"\",\""c"\"",\""d"\"]"
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#define _SONAME_ARRAY5(a, b, c, d, e) "[\""a"\",\""b"\",\""c"\"",\""d"\",\""e"\"]"
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#define _SONAME_ARRAY_GET(_1,_2,_3,_4,_5,NAME,...) NAME
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#define _SONAME_ARRAY(...) _SONAME_ARRAY_GET(__VA_ARGS__, _SONAME_ARRAY5, _SONAME_ARRAY4, _SONAME_ARRAY3, _SONAME_ARRAY2, _SONAME_ARRAY1)(__VA_ARGS__)
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/* The 'priority' must be one of 'required', 'recommended' or 'suggested' as per specification, use the
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* macro defined above to specify it.
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* Multiple sonames can be passed and they will be automatically constructed into a json array (but note that
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* due to preprocessor language limitations if more than the limit defined above is used, a new
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* _SONAME_ARRAY<X+1> will need to be added). */
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#define ELF_NOTE_DLOPEN(feature, description, priority, ...) \
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_ELF_NOTE_DLOPEN("[{\"feature\":\"" feature "\",\"description\":\"" description "\",\"priority\":\"" priority "\",\"soname\":" _SONAME_ARRAY(__VA_ARGS__) "}]", UNIQ_T(s, UNIQ))
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