[PATCH v2] track pthread stack guard sizes

[William Pitcock <nenolod@dereferenced.org>]

some applications (rustc) are dependent on pthread_getattr_np() providing the guard size.
---
 src/internal/pthread_impl.h     | 1 +
 src/thread/pthread_create.c     | 3 ++-
 src/thread/pthread_getattr_np.c | 1 +
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/internal/pthread_impl.h b/src/internal/pthread_impl.h
index f0b2c20c..4a0db987 100644
--- a/src/internal/pthread_impl.h
+++ b/src/internal/pthread_impl.h
@@ -46,6 +46,7 @@ struct pthread {
 	char *dlerror_buf;
 	int dlerror_flag;
 	void *stdio_locks;
+	size_t guard_size;
 	uintptr_t canary_at_end;
 	void **dtv_copy;
 };
diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index 34cd9936..439ee363 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -232,8 +232,8 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
 			memset(stack, 0, need);
 		} else {
 			size = ROUND(need);
-			guard = 0;
 		}
+		guard = 0;
 	} else {
 		guard = ROUND(attr._a_guardsize);
 		size = guard + ROUND(attr._a_stacksize
@@ -265,6 +265,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
 	new->map_size = size;
 	new->stack = stack;
 	new->stack_size = stack - stack_limit;
+	new->guard_size = guard;
 	new->start = entry;
 	new->start_arg = arg;
 	new->self = new;
diff --git a/src/thread/pthread_getattr_np.c b/src/thread/pthread_getattr_np.c
index ae26a5ab..29a209bd 100644
--- a/src/thread/pthread_getattr_np.c
+++ b/src/thread/pthread_getattr_np.c
@@ -7,6 +7,7 @@ int pthread_getattr_np(pthread_t t, pthread_attr_t *a)
 {
 	*a = (pthread_attr_t){0};
 	a->_a_detach = !!t->detached;
+	a->_a_guardsize = t->guard_size;
 	if (t->stack) {
 		a->_a_stackaddr = (uintptr_t)t->stack;
 		a->_a_stacksize = t->stack_size;
-- 
2.16.1