add C11 thread creation and related thread functions

based on patch by Jens Gustedt.

the main difficulty here is handling the difference between start
function signatures and thread return types for C11 threads versus
POSIX threads. pointers to void are assumed to be able to represent
faithfully all values of int. the function pointer for the thread
start function is cast to an incorrect type for passing through
pthread_create, but is cast back to its correct type before calling so
that the behavior of the call is well-defined.

changes to the existing threads implementation were kept minimal to
reduce the risk of regressions, and duplication of code that carries
implementation-specific assumptions was avoided for ease and safety of
future maintenance.

1 files changed, 12 insertions, 4 deletions

diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index c170a999..1a47ed15 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -119,7 +119,15 @@ static int start(void *p)
 	if (self->unblock_cancel)
 		__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK,
 			SIGPT_SET, 0, _NSIG/8);
-	pthread_exit(self->start(self->start_arg));
+	__pthread_exit(self->start(self->start_arg));
+	return 0;
+}
+
+static int start_c11(void *p)
+{
+	pthread_t self = p;
+	int (*start)(void*) = (int(*)(void*)) self->start;
+	__pthread_exit((void *)(uintptr_t)start(self->start_arg));
 	return 0;
 }
 
@@ -145,7 +153,7 @@ void *__copy_tls(unsigned char *);
 
 int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attrp, void *(*entry)(void *), void *restrict arg)
 {
-	int ret;
+	int ret, c11 = (attrp == __ATTRP_C11_THREAD);
 	size_t size, guard;
 	struct pthread *self, *new;
 	unsigned char *map = 0, *stack = 0, *tsd = 0, *stack_limit;
@@ -167,7 +175,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
 		self->tsd = (void **)__pthread_tsd_main;
 		libc.threaded = 1;
 	}
-	if (attrp) attr = *attrp;
+	if (attrp && !c11) attr = *attrp;
 
 	__acquire_ptc();
 
@@ -234,7 +242,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
 	new->canary = self->canary;
 
 	a_inc(&libc.threads_minus_1);
-	ret = __clone(start, stack, flags, new, &new->tid, TP_ADJ(new), &new->tid);
+	ret = __clone((c11 ? start_c11 : start), stack, flags, new, &new->tid, TP_ADJ(new), &new->tid);
 
 	__release_ptc();