Adapt rseq registration to glibc's userspace ABI for __rseq_abi

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/src/rseq.c b/src/rseq.c
index 6f39f092255cd5a901d9603d5493f05dcb7810dd..af431dd8b449a6293575143e372ec705a8ebce72 100644 (file)
--- a/src/rseq.c
+++ b/src/rseq.c
@@ -36,16 +36,6 @@ __thread struct rseq __rseq_abi = {
        .cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
 };
 
-/*
- * Shared with other libraries. This library may take rseq ownership if it is
- * still 0 when executing the library constructor. Set to 1 by library
- * constructor when handling rseq. Set to 0 in destructor if handling rseq.
- */
-int __rseq_handled;
-
-/* Whether this library have ownership of rseq registration. */
-static int rseq_ownership;
-
 static __thread uint32_t __rseq_refcount;
 
 static int sys_rseq(struct rseq *rseq_abi, uint32_t rseq_len,
@@ -93,27 +83,42 @@ static void signal_restore(sigset_t oldset)
 
 int rseq_register_current_thread(void)
 {
-       int rc, ret = 0;
+       int rc, ret = 0, cpu_id;
        sigset_t oldset;
 
-       if (!rseq_ownership)
-               return 0;
        signal_off_save(&oldset);
-       if (__rseq_refcount == UINT_MAX) {
+       cpu_id = rseq_current_cpu_raw();
+       if (cpu_id == RSEQ_CPU_ID_REGISTRATION_FAILED) {
+               errno = EPERM;
                ret = -1;
                goto end;
        }
-       if (__rseq_refcount++)
-               goto end;
-       rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
-       if (!rc) {
+       /*
+        * If cpu_id >= 0, rseq is already successfully registered either by
+        * libc (__rseq_refcount == 0) or by another user library
+        * (__rseq_refcount > 0) for this thread.
+        */
+       if (cpu_id >= 0) {
+               /* Treat libc's ownership as a successful registration. */
+               if (__rseq_refcount == 0)
+                       goto end;
+               if (__rseq_refcount == UINT_MAX) {
+                       errno = EOVERFLOW;
+                       ret = -1;
+                       goto end;
+               }
+       } else {
+               assert(__rseq_refcount == 0);
+               rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
+               if (rc) {
+                       assert(errno != EBUSY);
+                       __rseq_abi.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
+                       ret = -1;
+                       goto end;
+               }
                assert(rseq_current_cpu_raw() >= 0);
-               goto end;
        }
-       if (errno != EBUSY)
-               __rseq_abi.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
-       ret = -1;
-       __rseq_refcount--;
+       __rseq_refcount++;
 end:
        signal_restore(oldset);
        return ret;
@@ -121,24 +126,36 @@ end:
 
 int rseq_unregister_current_thread(void)
 {
-       int rc, ret = 0;
+       int rc, ret = 0, cpu_id;
        sigset_t oldset;
 
-       if (!rseq_ownership)
-               return 0;
        signal_off_save(&oldset);
-       if (!__rseq_refcount) {
+       cpu_id = rseq_current_cpu_raw();
+       /* cpu_id < 0 means rseq is either uninitialized or registration failed. */
+       if (cpu_id < 0) {
+               errno = EPERM;
                ret = -1;
                goto end;
        }
-       if (--__rseq_refcount)
-               goto end;
-       rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
-                     RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
-       if (!rc)
+       /*
+        * If cpu_id >= 0, rseq is currently successfully registered either by
+        * libc (__rseq_refcount == 0) or by another user library
+        * (__rseq_refcount > 0) for this thread.
+        *
+        * Treat libc's ownership as a successful unregistration.
+        */
+       if (__rseq_refcount == 0) {
                goto end;
-       __rseq_refcount = 1;
-       ret = -1;
+       }
+       if (__rseq_refcount == 1) {
+               rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
+                             RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
+               if (rc) {
+                       ret = -1;
+                       goto end;
+               }
+       }
+       __rseq_refcount--;
 end:
        signal_restore(oldset);
        return ret;
@@ -155,20 +172,3 @@ int32_t rseq_fallback_current_cpu(void)
        }
        return cpu;
 }
-
-void __attribute__((constructor)) rseq_init(void)
-{
-       /* Check whether rseq is handled by another library. */
-       if (__rseq_handled)
-               return;
-       __rseq_handled = 1;
-       rseq_ownership = 1;
-}
-
-void __attribute__((destructor)) rseq_fini(void)
-{
-       if (!rseq_ownership)
-               return;
-       __rseq_handled = 0;
-       rseq_ownership = 0;
-}