[Mesa-dev] [PATCH 17/18] loader: Look for any version of currently linked libudev.so

[Chris Wilson]

Since there was an ABI break and linking twice against libudev.so.0 and
libudev.so.1 causes the application to quickly crash, we first check if
the application is currently linked against libudev before dlopening a
local handle. However for backwards/forwards compatability, we need to
inspect the application for current linkage against all known versions
first.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 src/loader/loader.c | 46 ++++++++++++++++++++++++++++------------------
 1 file changed, 28 insertions(+), 18 deletions(-)

diff --git a/src/loader/loader.c b/src/loader/loader.c
index 8452cd3..8780587 100644
--- a/src/loader/loader.c
+++ b/src/loader/loader.c
@@ -128,26 +128,36 @@ static void *udev_handle = NULL;
 static void *
 udev_dlopen_handle(void)
 {
-   if (!udev_handle) {
-      udev_handle = dlopen("libudev.so.1", RTLD_LOCAL | RTLD_LAZY);
-
-      if (!udev_handle) {
-         /* libudev.so.1 changed the return types of the two unref functions
-          * from voids to pointers.  We don't use those return values, and the
-          * only ABI I've heard that cares about this kind of change (calling
-          * a function with a void * return that actually only returns void)
-          * might be ia64.
-          */
-         udev_handle = dlopen("libudev.so.0", RTLD_LOCAL | RTLD_LAZY);
-
-         if (!udev_handle) {
-            log_(_LOADER_WARNING, "Couldn't dlopen libudev.so.1 or "
-                 "libudev.so.0, driver detection may be broken.\n");
-         }
+   char name[80];
+   unsigned flags = RTLD_NOLOAD | RTLD_LOCAL | RTLD_LAZY;
+   int version;
+
+   /* libudev.so.1 changed the return types of the two unref functions
+    * from voids to pointers.  We don't use those return values, and the
+    * only ABI I've heard that cares about this kind of change (calling
+    * a function with a void * return that actually only returns void)
+    * might be ia64.
+    */
+
+   /* First try opening an already linked libudev, then try loading one */
+   do {
+      for (version = 1; version >= 0; version--) {
+         snprintf(name, sizeof(name), "libudev.so.%d", version);
+         udev_handle = dlopen(name, flags);
+         if (udev_handle)
+            return udev_handle;
       }
-   }
 
-   return udev_handle;
+      if ((flags & RTLD_NOLOAD) == 0)
+         break;
+
+      flags &= ~RTLD_NOLOAD;
+   } while (1);
+
+   log_(_LOADER_WARNING,
+        "Couldn't dlopen libudev.so.1 or "
+        "libudev.so.0, driver detection may be broken.\n");
+   return NULL;
 }
 
 static int dlsym_failed = 0;
-- 
2.1.4