snd_dlopen: implement the relocatable version for glibc

BugLink: https://github.com/alsa-project/alsa-lib/issues/34
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

include/global.h

@@ -97,6 +97,7 @@ extern struct snd_dlsym_link *snd_dlsym_start;
 /** \brief Returns the version of a dynamic symbol as a string. */
 #define SND_DLSYM_VERSION(version) __STRING(version)
 
+int snd_dlpath(char *path, size_t path_len, const char *name);
 void *snd_dlopen(const char *file, int mode, char *errbuf, size_t errbuflen);
 void *snd_dlsym(void *handle, const char *name, const char *version);
 int snd_dlclose(void *handle);

modules/mixer/simple/python.c

@@ -21,6 +21,7 @@
 
 #include "Python.h"
 #include <stddef.h>
+#include <limits.h>
 #include "config.h"
 #include "asoundlib.h"
 #include "mixer_abst.h"
@@ -36,7 +37,7 @@ struct python_priv {
 	PyObject *py_mixer;
 };
 
-#define SCRIPT ALSA_PLUGIN_DIR "/smixer/python/main.py"
+#define SCRIPT "smixer/python/main.py"
 
 struct pymelem {
 	PyObject_HEAD
@@ -1110,6 +1111,7 @@ int alsa_mixer_simple_finit(snd_mixer_class_t *class,
 	FILE *fp;
 	const char *file;
 	PyObject *obj, *py_mod;
+	char path[PATH_MAX];
 
 	priv = calloc(1, sizeof(*priv));
 	if (priv == NULL)
@@ -1119,8 +1121,10 @@ int alsa_mixer_simple_finit(snd_mixer_class_t *class,
 	snd_mixer_sbasic_set_private_free(class, alsa_mixer_simple_free);
 
 	file = getenv("ALSA_MIXER_SIMPLE_MPYTHON");
-	if (file == NULL)
+	if (file == NULL) {
-		file = SCRIPT;
+		snd_dlpath(path, sizeof(path), SCRIPT);
+		file = path;
+	}
 
 	fp = fopen(file, "r");
 	if (fp == NULL) {

src/dlmisc.c

@@ -32,6 +32,7 @@
 #ifdef HAVE_LIBPTHREAD
 #include <pthread.h>
 #endif
+#include <limits.h>
 
 #ifndef DOC_HIDDEN
 #ifndef PIC
@@ -39,6 +40,42 @@ struct snd_dlsym_link *snd_dlsym_start = NULL;
 #endif
 #endif
 
+/**
+ *
+ * \brief Compose the dynamic path
+ * \param path Returned path (string)
+ * \param path_len Returned path max size (with trailing zero)
+ * \param name Plugin name (relative)
+ * \return Zero on success, otherwise a negative error code
+ */
+int snd_dlpath(char *path, size_t path_len, const char *name)
+{
+	static const char *origin_dir = NULL;
+#ifdef HAVE_LIBDL
+#ifdef __GLIBC__
+	static int plugin_dir_set = 0;
+	if (!plugin_dir_set) {
+		struct link_map *links;
+		Dl_info info;
+		char origin[PATH_MAX];
+		if (dladdr1(&snd_dlpath, &info, (void**)&links, RTLD_DL_LINKMAP) == 0)
+			links = NULL;
+		if (links != NULL && dlinfo(links, RTLD_DI_ORIGIN, origin) == 0) {
+			snprintf(path, path_len, "%s/alsa-lib", origin);
+			if (access(path, X_OK) == 0)
+				origin_dir = origin;
+		}
+		plugin_dir_set = 1;
+	}
+#endif
+#endif
+	if (origin_dir)
+		snprintf(path, path_len, "%s/alsa-lib/%s", origin_dir, name);
+	else
+		snprintf(path, path_len, "%s/%s", ALSA_PLUGIN_DIR, name);
+	return 0;
+}
+
 /**
  * \brief Opens a dynamic library - ALSA wrapper for \c dlopen.
  * \param name name of the library, similar to \c dlopen.
@@ -79,14 +116,12 @@ void *snd_dlopen(const char *name, int mode, char *errbuf, size_t errbuflen)
 	 * via ld.so.conf.
 	 */
 	void *handle = NULL;
-	char *filename = NULL;
+	const char *filename = NULL;
+	char path[PATH_MAX];
 
 	if (name && name[0] != '/') {
-		filename = alloca(sizeof(ALSA_PLUGIN_DIR) + 1 + strlen(name) + 1);
+		if (snd_dlpath(path, sizeof(path), name) == 0) {
-		if (filename) {
+			filename = name;
-			strcpy(filename, ALSA_PLUGIN_DIR);
-			strcat(filename, "/");
-			strcat(filename, name);
 			handle = dlopen(filename, mode);
 			if (!handle) {
 				/* if the filename exists and cannot be opened */
@@ -97,6 +132,7 @@ void *snd_dlopen(const char *name, int mode, char *errbuf, size_t errbuflen)
 		}
 	}
 	if (!handle) {
+		filename = name;
 		handle = dlopen(name, mode);
 		if (!handle)
 			goto errpath;