Merge branch 'bug26779_033' into bug26779_035

changes/bug26779

@@ -0,0 +1,4 @@
+  o Minor features (bug workaround):
+    - Compile correctly on systems that provide the C11 stdatomic.h header,
+      but where C11 atomic functions don't actually compile.
+      Closes ticket 26779; workaround for Debian issue 903709.

configure.ac

@@ -1658,6 +1658,26 @@ AC_CHECK_SIZEOF(socklen_t, , [AC_INCLUDES_DEFAULT()
 
 AC_CHECK_SIZEOF(cell_t)
 
+# Let's see if stdatomic works. (There are some debian clangs that screw it
+# up; see Tor bug #26779 and debian bug 903709.)
+AC_CACHE_CHECK([whether C11 stdatomic.h actually works],
+               tor_cv_stdatomic_works,
+[AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+#include <stdatomic.h>
+struct x { atomic_size_t y; };
+void try_atomic_init(struct x *xx)
+{
+  atomic_init(&xx->y, 99);
+  atomic_fetch_add(&xx->y, 1);
+}
+]])], [tor_cv_stdatomic_works=yes], [tor_cv_stdatomic_works=no])])
+
+if test "$tor_cv_stdatomic_works" = "yes"; then
+   AC_DEFINE(STDATOMIC_WORKS, 1, [Set to 1 if we can compile a simple stdatomic example.])
+elif test "$ac_cv_header_stdatomic_h" = "yes"; then
+   AC_MSG_WARN([Your compiler provides the stdatomic.h header, but it doesn't seem to work.  I'll pretend it isn't there. If you are using Clang on Debian, maybe this is because of https://bugs.debian.org/903709 ])
+fi
+
 # Now make sure that NULL can be represented as zero bytes.
 AC_CACHE_CHECK([whether memset(0) sets pointers to NULL], tor_cv_null_is_zero,
 [AC_RUN_IFELSE([AC_LANG_SOURCE(

src/lib/thread/compat_threads.c

@@ -57,7 +57,7 @@ in_main_thread(void)
   return main_thread_id == tor_get_thread_id();
 }
 
-#ifndef HAVE_STDATOMIC_H
+#ifndef HAVE_WORKING_STDATOMIC
 /** Initialize a new atomic counter with the value 0 */
 void
 atomic_counter_init(atomic_counter_t *counter)
@@ -108,4 +108,4 @@ atomic_counter_exchange(atomic_counter_t *counter, size_t newval)
   tor_mutex_release(&counter->mutex);
   return oldval;
 }
-#endif /* !defined(HAVE_STDATOMIC_H) */
+#endif /* !defined(HAVE_WORKING_STDATOMIC) */

src/lib/thread/threads.h

@@ -16,7 +16,11 @@
 #include "lib/testsupport/testsupport.h"
 #include "lib/lock/compat_mutex.h"
 
-#ifdef HAVE_STDATOMIC_H
+#if defined(HAVE_STDATOMIC_H) && defined(STDATOMIC_WORKS)
+#define HAVE_WORKING_STDATOMIC
+#endif
+
+#ifdef HAVE_WORKING_STDATOMIC
 #include <stdatomic.h>
 #endif
 
@@ -98,18 +102,18 @@ void tor_threadlocal_set(tor_threadlocal_t *threadlocal, void *value);
 /**
  * Atomic counter type; holds a size_t value.
  */
-#ifdef HAVE_STDATOMIC_H
+#ifdef HAVE_WORKING_STDATOMIC
 typedef struct atomic_counter_t {
   atomic_size_t val;
 } atomic_counter_t;
 #define ATOMIC_LINKAGE static
-#else /* !(defined(HAVE_STDATOMIC_H)) */
+#else /* !(defined(HAVE_WORKING_STDATOMIC)) */
 typedef struct atomic_counter_t {
   tor_mutex_t mutex;
   size_t val;
 } atomic_counter_t;
 #define ATOMIC_LINKAGE
-#endif /* defined(HAVE_STDATOMIC_H) */
+#endif /* defined(HAVE_WORKING_STDATOMIC) */
 
 ATOMIC_LINKAGE void atomic_counter_init(atomic_counter_t *counter);
 ATOMIC_LINKAGE void atomic_counter_destroy(atomic_counter_t *counter);
@@ -120,7 +124,7 @@ ATOMIC_LINKAGE size_t atomic_counter_exchange(atomic_counter_t *counter,
                                               size_t newval);
 #undef ATOMIC_LINKAGE
 
-#ifdef HAVE_STDATOMIC_H
+#ifdef HAVE_WORKING_STDATOMIC
 /** Initialize a new atomic counter with the value 0 */
 static inline void
 atomic_counter_init(atomic_counter_t *counter)
@@ -158,7 +162,7 @@ atomic_counter_exchange(atomic_counter_t *counter, size_t newval)
   return atomic_exchange(&counter->val, newval);
 }
 
-#else /* !(defined(HAVE_STDATOMIC_H)) */
+#else /* !(defined(HAVE_WORKING_STDATOMIC)) */
-#endif /* defined(HAVE_STDATOMIC_H) */
+#endif /* defined(HAVE_WORKING_STDATOMIC) */
 
 #endif /* !defined(TOR_COMPAT_THREADS_H) */