Embed ELF metadata about dynamic runtime dependencies

Embed metadata about runtime dependencies of dynamic libraries used via dlopen(3) in the binary so that distributions can automatically generate package dependencies. Specification: https://systemd.io/ELF_DLOPEN_METADATA/ (TODO: link not yet available) Inspired-by: systemd/systemd#32234
htop-dev · May 18, 2024 · 7dc0ab1 · 7dc0ab1
1 parent 8dfe7ed
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diff --git a/Macros.h b/Macros.h
@@ -118,6 +118,15 @@ in the source distribution for its full text.
 #define IGNORE_WCASTQUAL_END
 #endif
 
+#if defined(__clang__)
+#define IGNORE_W11EXTENSIONS_BEGIN  _Pragma("clang diagnostic push") \
+                                    _Pragma("clang diagnostic ignored \"-Wc11-extensions\"")
+#define IGNORE_W11EXTENSIONS_END    _Pragma("clang diagnostic pop")
+#else
+#define IGNORE_W11EXTENSIONS_BEGIN
+#define IGNORE_W11EXTENSIONS_END
+#endif
+
 /* Cheaper function for checking NaNs. Unlike the standard isnan(), this may
    throw an FP exception on a "signaling NaN".
    (ISO/IEC TS 18661-1 and the C23 standard stated that isnan() throws no
@@ -142,4 +151,32 @@ static inline unsigned long long saturatingSub(unsigned long long a, unsigned lo
    return a > b ? a - b : 0;
 }
 
+#ifdef HAVE_ALIGNAS
+#include <stdalign.h>
+
+#define ELF_NOTE_DLOPEN_OWNER "FDO"
+#define ELF_NOTE_DLOPEN_TYPE  UINT32_C(0x407c0c0a)
+
+#define DECLARE_ELF_NOTE_DLOPEN(content) \
+   IGNORE_W11EXTENSIONS_BEGIN                                                                      \
+   __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_OWNER)];                                                    \
+      alignas(sizeof(uint32_t)) char dlopen_content[sizeof(content)];                              \
+   } variable_name = {                                                                             \
+      .nhdr = {                                                                                    \
+         .n_namesz = sizeof(ELF_NOTE_DLOPEN_OWNER),                                                \
+         .n_descsz = sizeof(content),                                                              \
+         .n_type   = ELF_NOTE_DLOPEN_TYPE,                                                         \
+      },                                                                                           \
+      .name = ELF_NOTE_DLOPEN_OWNER,                                                               \
+      .dlopen_content = content,                                                                   \
+   };                                                                                              \
+   IGNORE_W11EXTENSIONS_END
+#else
+#define DECLARE_ELF_NOTE_DLOPEN()
 #endif
+
+#endif /* HEADER_Macros */
diff --git a/README.md b/README.md
@@ -162,6 +162,9 @@ On most BSD systems `kvm` is a requirement to read kernel information.
 
 More information on required and optional dependencies can be found in [configure.ac](configure.ac).
 
+#### ELF Note
+The optional runtime dependencies are also embedded in the binary via the ELF note `.note.dlopen`. See the [specification](https://systemd.io/ELF_DLOPEN_METADATA/) for details.
+
 ## Usage
 See the manual page (`man htop`) or the help menu (**F1** or **h** inside `htop`) for a list of supported key commands.
 

diff --git a/configure.ac b/configure.ac
@@ -273,6 +273,18 @@ AC_LINK_IFELSE([
    [AC_MSG_RESULT(no)
    AC_MSG_ERROR([can not find required macros: NAN, isgreater() and isgreaterequal()])])
 
+AC_MSG_CHECKING(for alignas support)
+AC_COMPILE_IFELSE([
+   AC_LANG_SOURCE(
+      [[
+         #include <stdalign.h>
+         alignas(128) char buffer[128];
+      ]]
+   )],
+   AC_DEFINE([HAVE_ALIGNAS], 1, [The alignas C11 feauture is supported.])
+   AC_MSG_RESULT(yes),
+   AC_MSG_RESULT(no))
+
 # ----------------------------------------------------------------------
 
 

diff --git a/linux/LibNl.c b/linux/LibNl.c
@@ -75,6 +75,12 @@ static void unload_libnl(void) {
 }
 
 static int load_libnl(void) {
+
+   DECLARE_ELF_NOTE_DLOPEN("[{\"soname\":[\"libnl-3.so\",\"libnl-3.so.200\"],\"feature\":\"delay-accounting\"," \
+      "\"description:\":\"Enables delay accounting support\",\"priority\":\"recommended\"},{\"soname\":[" \
+      "\"libnl-genl-3.so\",\"libnl-genl-3.so.200\"],\"feature\":\"delay-accounting\",\"description:\":"\
+      "\"Enables delay accounting support\",\"priority\":\"recommended\"}]")
+
    if (libnlHandle && libnlGenlHandle)
       return 0;
 

diff --git a/linux/LibSensors.c b/linux/LibSensors.c
@@ -56,6 +56,9 @@ int LibSensors_init(void) {
 
 #else
 
+   DECLARE_ELF_NOTE_DLOPEN("[{\"soname\":[\"libsensors.so\",\"libsensors.so.5\",\"libsensors.so.4\"],\"feature\":"\
+      "\"sensors\",\"description:\":\"Enables hardware sensor support\",\"priority\":\"recommended\"}]")
+
    if (!dlopenHandle) {
       /* Find the unversioned libsensors.so (symlink) and prefer that, but Debian has .so.5 and Fedora .so.4 without
          matching symlinks (unless people install the -dev packages) */

diff --git a/linux/SystemdMeter.c b/linux/SystemdMeter.c
@@ -98,6 +98,9 @@ static void SystemdMeter_done(ATTR_UNUSED Meter* this) {
 static int updateViaLib(bool user) {
    SystemdMeterContext_t* ctx = user ? &ctx_user : &ctx_system;
 #ifndef BUILD_STATIC
+   DECLARE_ELF_NOTE_DLOPEN("[{\"soname\":[\"libsystemd.so.0\"],\"feature\":\"systemd\",\"description:\":"\
+      "\"Enables systemd support\",\"priority\":\"suggested\"}]")
+
    if (!dlopenHandle) {
       dlopenHandle = dlopen("libsystemd.so.0", RTLD_LAZY);
       if (!dlopenHandle)