conf: fix thread_local support detection

configure.ac

@@ -629,7 +629,7 @@ AC_CHECK_DECLS([PR_SET_NO_NEW_PRIVS], [], [], [#include <sys/prctl.h>])
 AC_CHECK_DECLS([PR_GET_NO_NEW_PRIVS], [], [], [#include <sys/prctl.h>])
 
 # Check for some headers
-AC_CHECK_HEADERS([pty.h sys/memfd.h sys/personality.h sys/resource.h sys/signalfd.h sys/timerfd.h utmpx.h])
+AC_CHECK_HEADERS([pty.h sys/memfd.h sys/personality.h sys/resource.h sys/signalfd.h sys/timerfd.h utmpx.h threads.h])
 
 AC_CHECK_HEADER([ifaddrs.h],
 	AM_CONDITIONAL(HAVE_IFADDRS_H, true)

src/lxc/compiler.h

@@ -12,14 +12,23 @@
 
 #include "config.h"
 
-#ifndef thread_local
-#if __STDC_VERSION__ >= 201112L &&    \
-    !(defined(__STDC_NO_THREADS__) || \
-      (defined(__GNU_LIBRARY__) && __GLIBC__ == 2 && __GLIBC_MINOR__ < 16))
-#define thread_local _Thread_local
+#if defined(HAVE_THREADS_H)
+	#include <threads.h>
+	#define THREAD_LOCAL_STORAGE_SUPPORTED
+#elif defined(thread_local)
+	#define THREAD_LOCAL_STORAGE_SUPPORTED
 #else
-#define thread_local __thread
-#endif
+	#if __STDC_VERSION__ >= 201112L &&    \
+	    !(defined(__STDC_NO_THREADS__) || \
+	      (defined(__GNU_LIBRARY__) && __GLIBC__ == 2 && __GLIBC_MINOR__ < 16))
+		#define thread_local _Thread_local
+
+		#define THREAD_LOCAL_STORAGE_SUPPORTED
+	#else
+		#define thread_local __thread
+
+		#define THREAD_LOCAL_STORAGE_SUPPORTED
+	#endif
 #endif
 
 #if __GNUC__ >= 7

src/lxc/conf.c

@@ -36,6 +36,7 @@
 #include "af_unix.h"
 #include "caps.h"
 #include "cgroups/cgroup.h"
+#include "compiler.h"
 #include "conf.h"
 #include "config.h"
 #include "confile.h"
@@ -99,11 +100,14 @@
 
 lxc_log_define(conf, lxc);
 
-/* The lxc_conf of the container currently being worked on in an API call.
+/*
+ * The lxc_conf of the container currently being worked on in an API call.
  * This is used in the error calls.
  */
-#ifdef HAVE_TLS
+#if defined(THREAD_LOCAL_STORAGE_SUPPORTED)
 thread_local struct lxc_conf *current_config;
+#elif defined(ENFORCE_THREAD_SAFETY)
+#error ENFORCE_THREAD_SAFETY was set but cannot be guaranteed due to missing TLS
 #else
 struct lxc_conf *current_config;
 #endif

src/lxc/conf.h

@@ -474,10 +474,12 @@ struct lxc_conf {
 __hidden extern int write_id_mapping(enum idtype idtype, pid_t pid, const char *buf, size_t buf_size)
     __access_r(3, 4);
 
-#ifdef HAVE_TLS
+#if defined(THREAD_LOCAL_STORAGE_SUPPORTED)
 extern thread_local struct lxc_conf *current_config;
+#elif defined(ENFORCE_THREAD_SAFETY)
+#error ENFORCE_THREAD_SAFETY was set but cannot be guaranteed due to missing TLS
 #else
-extern struct lxc_conf *current_config;
+struct lxc_conf *current_config;
 #endif
 
 __hidden extern int run_lxc_hooks(const char *name, char *hook, struct lxc_conf *conf, char *argv[]);

src/lxc/initutils.c

@@ -54,8 +54,10 @@ const char *lxc_global_config_value(const char *option_name)
 	};
 
 	/* placed in the thread local storage pool for non-bionic targets */
-#ifdef HAVE_TLS
+#if defined(THREAD_LOCAL_STORAGE_SUPPORTED)
 	static thread_local const char *values[sizeof(options) / sizeof(options[0])] = {0};
+#elif defined(ENFORCE_THREAD_SAFETY)
+	#error ENFORCE_THREAD_SAFETY was set but cannot be guaranteed due to missing TLS
 #else
 	static const char *values[sizeof(options) / sizeof(options[0])] = {0};
 #endif