add pthread_attr_setstack interface (and get)

i originally omitted these (optional, per POSIX) interfaces because i
considered them backwards implementation details. however, someone
later brought to my attention a fairly legitimate use case: allocating
thread stacks in memory that's setup for sharing and/or fast transfer
between CPU and GPU so that the thread can move data to a GPU directly
from automatic-storage buffers without having to go through additional
buffer copies.

perhaps there are other situations in which these interfaces are
useful too.

diff --git a/src/internal/pthread_impl.h b/src/internal/pthread_impl.h
index d67edf2..0ce3c1e 100644 (file)
--- a/src/internal/pthread_impl.h
+++ b/src/internal/pthread_impl.h
@@ -59,7 +59,8 @@ struct __timer {
 
 #define _a_stacksize __u.__s[0]
 #define _a_guardsize __u.__s[1]
-#define _a_detach __u.__i[2*__SU+0]
+#define _a_stackaddr __u.__s[2]
+#define _a_detach __u.__i[3*__SU+0]
 #define _m_type __u.__i[0]
 #define _m_lock __u.__i[1]
 #define _m_waiters __u.__i[2]

diff --git a/src/thread/pthread_attr_getstack.c b/src/thread/pthread_attr_getstack.c
new file mode 100644 (file)
index 0000000..07ac592
--- /dev/null
+++ b/src/thread/pthread_attr_getstack.c
@@ -0,0 +1,10 @@
+#include "pthread_impl.h"
+
+int pthread_attr_getstack(const pthread_attr_t *a, void **addr, size_t *size)
+{
+       if (!a->_a_stackaddr)
+               return EINVAL;
+       *size = a->_a_stacksize + DEFAULT_STACK_SIZE;
+       *addr = (void *)(a->_a_stackaddr - *size);
+       return 0;
+}

diff --git a/src/thread/pthread_attr_setstack.c b/src/thread/pthread_attr_setstack.c
new file mode 100644 (file)
index 0000000..c51ad34
--- /dev/null
+++ b/src/thread/pthread_attr_setstack.c
@@ -0,0 +1,14 @@
+#include "pthread_impl.h"
+
+/* pthread_key_create.c overrides this */
+static const size_t dummy = 0;
+weak_alias(dummy, __pthread_tsd_size);
+
+int pthread_attr_setstack(pthread_attr_t *a, void *addr, size_t size)
+{
+       if (size-PTHREAD_STACK_MIN-__pthread_tsd_size > SIZE_MAX/4)
+               return EINVAL;
+       a->_a_stackaddr = (size_t)addr + size;
+       a->_a_stacksize = size - DEFAULT_STACK_SIZE;
+       return 0;
+}

diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index 5b34e7e..48290d3 100644 (file)
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -98,16 +98,20 @@ int pthread_create(pthread_t *res, const pthread_attr_t *attr, void *(*entry)(vo
                libc.threaded = 1;
        }
 
-       if (attr) {
-               guard = ROUND(attr->_a_guardsize + DEFAULT_GUARD_SIZE);
-               size = guard + ROUND(attr->_a_stacksize + DEFAULT_STACK_SIZE);
+       if (attr && attr->_a_stackaddr) {
+               map = 0;
+               tsd = (void *)(attr->_a_stackaddr-__pthread_tsd_size & -16);
+       } else {
+               if (attr) {
+                       guard = ROUND(attr->_a_guardsize + DEFAULT_GUARD_SIZE);
+                       size = guard + ROUND(attr->_a_stacksize + DEFAULT_STACK_SIZE);
+               }
+               size += __pthread_tsd_size;
+               map = mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0);
+               if (map == MAP_FAILED) return EAGAIN;
+               if (guard) mprotect(map, guard, PROT_NONE);
+               tsd = map + size - __pthread_tsd_size;
        }
-       size += __pthread_tsd_size;
-       map = mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0);
-       if (map == MAP_FAILED) return EAGAIN;
-       if (guard) mprotect(map, guard, PROT_NONE);
-
-       tsd = map + size - __pthread_tsd_size;
        new = (void *)(tsd - sizeof *new - PAGE_SIZE%sizeof *new);
        new->map_base = map;
        new->map_size = size;