the main programs handle does not provide enough information to call dlsym and find references to libunwind. An extra step extracts the path to the wheel's libunwind.so

Author: planrich

src/vmp_stack.c

@@ -511,28 +511,52 @@ static const char * vmprof_error = NULL;
 static void * libhandle = NULL;
 
 #ifdef VMPROF_LINUX
+#include <link.h>
 #define LIBUNWIND "libunwind.so"
 #ifdef __i386__
 #define PREFIX "x86"
+#define LIBUNWIND_SUFFIX ""
 #elif __x86_64__
 #define PREFIX "x86_64"
+#define LIBUNWIND_SUFFIX "-x86_64"
 #endif
 #define U_PREFIX "_U"
 #define UL_PREFIX "_UL"
 #endif
 
 int vmp_native_enable(void) {
 #ifdef VMPROF_LINUX
+    void * oldhandle = NULL;
+    struct link_map * map = NULL;
     if (libhandle == NULL) {
         // on linux, the wheel includes the libunwind shared object.
-        libhandle = dlopen(NULL, RTLD_LAZY | RTLD_LOCAL);
+        libhandle = dlopen(NULL, RTLD_NOW);
         if (libhandle != NULL) {
-            if (dlsym(libhandle, U_PREFIX PREFIX "_getcontext") != NULL) {
-                goto loaded_libunwind;
+            // load the link map, it will contain an entry to
+            // .libs_vmprof/libunwind-...so, this is the file that is
+            // distributed with the wheel.
+            if (dlinfo(libhandle, RTLD_DI_LINKMAP, &map) != 0) {
+                (void)dlclose(libhandle);
+                libhandle = NULL;
+                goto bail_out;
             }
+            // grab the new handle
+            do {
+                if (strstr(map->l_name, ".libs_vmprof/libunwind" LIBUNWIND_SUFFIX) != NULL) {
+                    oldhandle = libhandle;
+                    libhandle = dlopen(map->l_name, RTLD_LAZY|RTLD_LOCAL);
+                    (void)dlclose(oldhandle);
+                    oldhandle = NULL;
+                    goto loaded_libunwind;
+                }
+                map = map->l_next;
+            } while (map != NULL);
+            // did not find .libs_vmprof/libunwind...
+            (void)dlclose(libhandle);
             libhandle = NULL;
         }
 
+        // fallback! try to load the system's libunwind.so
         if ((libhandle = dlopen(LIBUNWIND, RTLD_LAZY | RTLD_LOCAL)) == NULL) {
             goto bail_out;
         }