shared/elf-note.h

/* SPDX-License-Identifier: LGPL-2.1-or-later */
#pragma once

#include "macro.h"

/*
 * Originally from systemd codebase.
 *
 * Reference: https://systemd.io/ELF_PACKAGE_METADATA/
 */

// clang-format off

#define ELF_NOTE_DLOPEN_VENDOR "FDO"
#define ELF_NOTE_DLOPEN_TYPE UINT32_C(0x407c0c0a)
#define ELF_NOTE_DLOPEN_PRIORITY_REQUIRED "required"
#define ELF_NOTE_DLOPEN_PRIORITY_RECOMMENDED "recommended"
#define ELF_NOTE_DLOPEN_PRIORITY_SUGGESTED "suggested"

/* Add an ".note.dlopen" ELF note to our binary that declares our weak dlopen() dependency. This
 * information can be read from an ELF file via "readelf -p .note.dlopen" or an equivalent command. */
#define _ELF_NOTE_DLOPEN(json, variable_name)                              \
        __attribute__((used, section(".note.dlopen"))) _Alignas(sizeof(uint32_t)) static const struct { \
                struct {                                                   \
                        uint32_t n_namesz, n_descsz, n_type;               \
                } nhdr;                                                    \
                char name[sizeof(ELF_NOTE_DLOPEN_VENDOR)];                 \
                _Alignas(sizeof(uint32_t)) char dlopen_json[sizeof(json)]; \
        } variable_name = {                                                \
                .nhdr = {                                                  \
                        .n_namesz = sizeof(ELF_NOTE_DLOPEN_VENDOR),        \
                        .n_descsz = sizeof(json),                          \
                        .n_type   = ELF_NOTE_DLOPEN_TYPE,                  \
                },                                                         \
                .name = ELF_NOTE_DLOPEN_VENDOR,                            \
                .dlopen_json = json,                                       \
        }

#define _SONAME_ARRAY1(a) "[\""a"\"]"
#define _SONAME_ARRAY2(a, b) "[\""a"\",\""b"\"]"
#define _SONAME_ARRAY3(a, b, c) "[\""a"\",\""b"\",\""c"\"]"
#define _SONAME_ARRAY4(a, b, c, d) "[\""a"\",\""b"\",\""c"\"",\""d"\"]"
#define _SONAME_ARRAY5(a, b, c, d, e) "[\""a"\",\""b"\",\""c"\"",\""d"\",\""e"\"]"
#define _SONAME_ARRAY_GET(_1,_2,_3,_4,_5,NAME,...) NAME
#define _SONAME_ARRAY(...) _SONAME_ARRAY_GET(__VA_ARGS__, _SONAME_ARRAY5, _SONAME_ARRAY4, _SONAME_ARRAY3, _SONAME_ARRAY2, _SONAME_ARRAY1)(__VA_ARGS__)

/* The 'priority' must be one of 'required', 'recommended' or 'suggested' as per specification, use the
 * macro defined above to specify it.
 * Multiple sonames can be passed and they will be automatically constructed into a json array (but note that
 * due to preprocessor language limitations if more than the limit defined above is used, a new
 * _SONAME_ARRAY<X+1> will need to be added). */
#define ELF_NOTE_DLOPEN(feature, description, priority, ...) \
        _ELF_NOTE_DLOPEN("[{\"feature\":\"" feature "\",\"description\":\"" description "\",\"priority\":\"" priority "\",\"soname\":" _SONAME_ARRAY(__VA_ARGS__) "}]", UNIQ_T(s, UNIQ))