Use rseq for cpu_id in libringbuffer

[lttng-ust.git] / libringbuffer / rseq.c

diff --git a/libringbuffer/rseq.c b/libringbuffer/rseq.c
index 219f416eabf3c5c14f7f1aab0ec0dcf3a2d2be22..0be7d10bd7236195ba9ce5204bae1a0a51fa93fd 100644 (file)
--- a/libringbuffer/rseq.c
+++ b/libringbuffer/rseq.c
@@ -31,10 +31,24 @@ __attribute__((weak)) __thread volatile struct rseq __rseq_abi = {
        .u.e.cpu_id = -1,
 };
 
+/* Own state, not shared with other libs. */
+static __thread int rseq_registered;
+
+static pthread_key_t rseq_key;
+
+
+#ifdef __NR_rseq
 static int sys_rseq(volatile struct rseq *rseq_abi, int flags)
 {
        return syscall(__NR_rseq, rseq_abi, flags);
 }
+#else
+static int sys_rseq(volatile struct rseq *rseq_abi, int flags)
+{
+       errno = ENOSYS;
+       return -1;
+}
+#endif
 
 static void signal_off_save(sigset_t *oldset)
 {
@@ -56,29 +70,82 @@ static void signal_restore(sigset_t oldset)
                abort();
 }
 
+int rseq_unregister_current_thread(void)
+{
+       sigset_t oldset;
+       int rc, ret = 0;
+
+       signal_off_save(&oldset);
+       if (rseq_registered) {
+               rc = sys_rseq(NULL, 0);
+               if (rc) {
+                       fprintf(stderr, "Error: sys_rseq(...) failed(%d): %s\n",
+                               errno, strerror(errno));
+                       ret = -1;
+                       goto end;
+               }
+               rseq_registered = 0;
+       }
+end:
+       signal_restore(oldset);
+       return ret;
+}
+
+static void destroy_rseq_key(void *key)
+{
+       if (rseq_unregister_current_thread())
+               abort();
+}
+
 int rseq_register_current_thread(void)
 {
-       int rc;
+       sigset_t oldset;
+       int rc, ret = 0;
 
-       rc = sys_rseq(&__rseq_abi, 0);
-       if (rc) {
-               fprintf(stderr, "Error: sys_rseq(...) failed(%d): %s\n",
-                       errno, strerror(errno));
-               return -1;
+       signal_off_save(&oldset);
+       if (caa_likely(!rseq_registered)) {
+               rc = sys_rseq(&__rseq_abi, 0);
+               if (rc) {
+                       fprintf(stderr, "Error: sys_rseq(...) failed(%d): %s\n",
+                               errno, strerror(errno));
+                       __rseq_abi.u.e.cpu_id = -2;
+                       ret = -1;
+                       goto end;
+               }
+               rseq_registered = 1;
+               assert(rseq_current_cpu_raw() >= 0);
+               /*
+                * Register destroy notifier. Pointer needs to
+                * be non-NULL.
+                */
+               if (pthread_setspecific(rseq_key, (void *)0x1))
+                       abort();
        }
-       assert(rseq_current_cpu() >= 0);
-       return 0;
+end:
+       signal_restore(oldset);
+       return ret;
 }
 
-int rseq_unregister_current_thread(void)
+void rseq_init(void)
 {
-       int rc;
+       int ret;
 
-       rc = sys_rseq(NULL, 0);
-       if (rc) {
-               fprintf(stderr, "Error: sys_rseq(...) failed(%d): %s\n",
-                       errno, strerror(errno));
-               return -1;
+       ret = pthread_key_create(&rseq_key, destroy_rseq_key);
+       if (ret) {
+               errno = -ret;
+               perror("pthread_key_create");
+               abort();
+       }
+}
+
+void rseq_destroy(void)
+{
+       int ret;
+
+       ret = pthread_key_delete(rseq_key);
+       if (ret) {
+               errno = -ret;
+               perror("pthread_key_delete");
+               abort();
        }
-       return 0;
 }