From: Lucas De Marchi Date: Wed, 4 Dec 2024 15:24:49 +0000 (-0600) Subject: libkmod: Add ELF notes to compression libraries X-Git-Tag: v34~28 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c9f80c49b1cb8218fa08fd415586d265771eeeb2;p=thirdparty%2Fkmod.git libkmod: Add ELF notes to compression libraries Follow the new spec for ELF notes as detailed in https://systemd.io/ELF_PACKAGE_METADATA/. We can copy mostly verbatim the macros from systemd codebase. Example output: $ meson setup --native-file build-dev.ini -Dxz=disabled -Ddlopen=zlib build ... dlopen : zlib features : +ZSTD -XZ +ZLIB +OPENSSL $ dlopen-notes.py build/libkmod.so.2 # build/libkmod.so.2 [ { "feature": "xz", "description": "Support for uncompressing xz-compressed modules", "priority": "recommended", "soname": [ "liblzma.so.5" ] } ] Signed-off-by: Lucas De Marchi Reviewed-by: Emil Velikov Link: https://github.com/kmod-project/kmod/pull/262 --- diff --git a/Makefile.am b/Makefile.am index e8ff6318..504af5b2 100644 --- a/Makefile.am +++ b/Makefile.am @@ -58,6 +58,7 @@ noinst_LTLIBRARIES = shared/libshared.la shared_libshared_la_SOURCES = \ shared/array.c \ shared/array.h \ + shared/elf-note.h \ shared/hash.c \ shared/hash.h \ shared/macro.h \ diff --git a/libkmod/libkmod-file-xz.c b/libkmod/libkmod-file-xz.c index f769f835..f6938770 100644 --- a/libkmod/libkmod-file-xz.c +++ b/libkmod/libkmod-file-xz.c @@ -14,6 +14,7 @@ #include #include +#include #include #include "libkmod.h" @@ -29,12 +30,16 @@ DL_SYMBOL_TABLE(DECLARE_SYM) static int dlopen_lzma(void) { +#if !DLSYM_LOCALLY_ENABLED + return 0; +#else static void *dl = NULL; - if (!DLSYM_LOCALLY_ENABLED) - return 0; + ELF_NOTE_DLOPEN("xz", "Support for uncompressing xz-compressed modules", + ELF_NOTE_DLOPEN_PRIORITY_RECOMMENDED, "liblzma.so.5"); return dlsym_many(&dl, "liblzma.so.5", DL_SYMBOL_TABLE(DLSYM_ARG) NULL); +#endif } static void xz_uncompress_belch(struct kmod_file *file, lzma_ret ret) diff --git a/libkmod/libkmod-file-zlib.c b/libkmod/libkmod-file-zlib.c index f8ead1b9..b26c7d1e 100644 --- a/libkmod/libkmod-file-zlib.c +++ b/libkmod/libkmod-file-zlib.c @@ -14,6 +14,7 @@ #include #include +#include #include #include "libkmod.h" @@ -32,12 +33,16 @@ DL_SYMBOL_TABLE(DECLARE_SYM) static int dlopen_zlib(void) { +#if !DLSYM_LOCALLY_ENABLED + return 0; +#else static void *dl = NULL; - if (!DLSYM_LOCALLY_ENABLED) - return 0; + ELF_NOTE_DLOPEN("zlib", "Support for uncompressing zlib-compressed modules", + ELF_NOTE_DLOPEN_PRIORITY_RECOMMENDED, "libz.so.1"); return dlsym_many(&dl, "libz.so.1", DL_SYMBOL_TABLE(DLSYM_ARG) NULL); +#endif } int kmod_file_load_zlib(struct kmod_file *file) diff --git a/libkmod/libkmod-file-zstd.c b/libkmod/libkmod-file-zstd.c index a2eece7d..f403a01b 100644 --- a/libkmod/libkmod-file-zstd.c +++ b/libkmod/libkmod-file-zstd.c @@ -15,6 +15,7 @@ #include #include +#include #include #include "libkmod.h" @@ -31,12 +32,16 @@ DL_SYMBOL_TABLE(DECLARE_SYM) static int dlopen_zstd(void) { +#if !DLSYM_LOCALLY_ENABLED + return 0; +#else static void *dl = NULL; - if (!DLSYM_LOCALLY_ENABLED) - return 0; + ELF_NOTE_DLOPEN("zstd", "Support for uncompressing zstd-compressed modules", + ELF_NOTE_DLOPEN_PRIORITY_RECOMMENDED, "libzstd.so.1"); return dlsym_many(&dl, "libzstd.so.1", DL_SYMBOL_TABLE(DLSYM_ARG) NULL); +#endif } int kmod_file_load_zstd(struct kmod_file *file) diff --git a/meson.build b/meson.build index 64288dd9..7e7c0209 100644 --- a/meson.build +++ b/meson.build @@ -363,6 +363,7 @@ libshared = static_library( files( 'shared/array.c', 'shared/array.h', + 'shared/elf-note.h', 'shared/hash.c', 'shared/hash.h', 'shared/macro.h', diff --git a/shared/elf-note.h b/shared/elf-note.h new file mode 100644 index 00000000..f29e2a5f --- /dev/null +++ b/shared/elf-note.h @@ -0,0 +1,53 @@ +/* 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 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)) diff --git a/shared/macro.h b/shared/macro.h index 7b4ea421..4cbdc7aa 100644 --- a/shared/macro.h +++ b/shared/macro.h @@ -37,6 +37,7 @@ #define XCONCATENATE(x, y) x##y #define CONCATENATE(x, y) XCONCATENATE(x, y) #define UNIQ(x) CONCATENATE(x, __COUNTER__) +#define UNIQ_T(x, uniq) CONCATENATE(__unique_prefix_, CONCATENATE(x, uniq)) /* Attributes */