add limited pthread_setattr_default_np API to set stack size defaults

based on patch by Timo Teräs:

While generally this is a bad API, it is the only existing API to
affect c++ (std::thread) and c11 (thrd_create) thread stack size.
This patch allows applications only to increate stack and guard
page sizes.

1 files changed, 35 insertions, 0 deletions

diff --git a/src/thread/pthread_setattr_default_np.c b/src/thread/pthread_setattr_default_np.c
new file mode 100644
index 00000000..ffd2712b
--- /dev/null
+++ b/src/thread/pthread_setattr_default_np.c
@@ -0,0 +1,35 @@
+#include "pthread_impl.h"
+#include <string.h>
+
+extern size_t __default_stacksize;
+extern size_t __default_guardsize;
+
+int pthread_setattr_default_np(const pthread_attr_t *attrp)
+{
+	/* Reject anything in the attr object other than stack/guard size. */
+	pthread_attr_t tmp = *attrp, zero = { 0 };
+	tmp._a_stacksize = 0;
+	tmp._a_guardsize = 0;
+	if (memcmp(&tmp, &zero, sizeof tmp))
+		return EINVAL;
+
+	__inhibit_ptc();
+	if (attrp->_a_stacksize >= __default_stacksize)
+		__default_stacksize = attrp->_a_stacksize;
+	if (attrp->_a_guardsize >= __default_guardsize)
+		__default_guardsize = attrp->_a_guardsize;
+	__release_ptc();
+
+	return 0;
+}
+
+int pthread_getattr_default_np(pthread_attr_t *attrp)
+{
+	__acquire_ptc();
+	*attrp = (pthread_attr_t) {
+		._a_stacksize = __default_stacksize,
+		._a_guardsize = __default_guardsize,
+	};
+	__release_ptc();
+	return 0;
+}