further debloat cancellation handlers

cleanup push and pop are also no-ops if pthread_exit is not reachable.
this can make a big difference for library code which needs to protect
itself against cancellation, but which is unlikely to actually be used
in programs with threads/cancellation.

src/thread/cancellation.c

 #include "pthread_impl.h"
 
-#ifdef __pthread_register_cancel
-#undef __pthread_register_cancel
-#undef __pthread_unregister_cancel
-#undef __pthread_unwind_next
-#define __pthread_register_cancel __pthread_register_cancel_3
-#define __pthread_unregister_cancel __pthread_unregister_cancel_3
-#define __pthread_unwind_next __pthread_unwind_next_3
-#endif
-
 static void dummy(struct __ptcb *cb)
 {
 }
 weak_alias(dummy, __pthread_do_unwind);
+weak_alias(dummy, __pthread_do_register);
+weak_alias(dummy, __pthread_do_unregister);
 
 void __pthread_unwind_next(struct __ptcb *cb)
 {
@@ -21,13 +14,10 @@ void __pthread_unwind_next(struct __ptcb *cb)
 
 void __pthread_register_cancel(struct __ptcb *cb)
 {
-	struct pthread *self = pthread_self();
-	cb->__next = self->cancelbuf;
-	self->cancelbuf = cb;
+	__pthread_do_register(cb);
 }
 
 void __pthread_unregister_cancel(struct __ptcb *cb)
 {
-	struct pthread *self = __pthread_self();
-	self->cancelbuf = self->cancelbuf->__next;
+	__pthread_do_unregister(cb);
 }

src/thread/i386/cancellation2.s → src/thread/i386/cancellation.s

@@ -3,7 +3,7 @@
 .type   __pthread_register_cancel,@function
 __pthread_register_cancel:
 	pushl %eax
-	call __pthread_register_cancel_3
+	call __pthread_do_register
 	popl %eax
 	ret
 
@@ -11,7 +11,7 @@ __pthread_register_cancel:
 .type   __pthread_unregister_cancel,@function
 __pthread_unregister_cancel:
 	pushl %eax
-	call __pthread_unregister_cancel_3
+	call __pthread_do_unregister
 	popl %eax
 	ret
 
@@ -19,6 +19,16 @@ __pthread_unregister_cancel:
 .type   __pthread_unwind_next,@function
 __pthread_unwind_next:
 	pushl %eax
-	call __pthread_unwind_next_3
+	call __pthread_do_unwind
 	popl %eax
+__pthread_do_unwind:
+__pthread_do_register:
+__pthread_do_unregister:
 	ret
+
+.weak __pthread_do_unwind
+.weak __pthread_do_register
+.weak __pthread_do_unregister
+.type __pthread_do_unwind,@function
+.type __pthread_do_register,@function
+.type __pthread_do_unregister,@function

src/thread/pthread_create.c

@@ -39,6 +39,19 @@ void __pthread_do_unwind(struct __ptcb *cb)
 	__syscall(SYS_exit, 0);
 }
 
+void __pthread_do_register(struct __ptcb *cb)
+{
+	struct pthread *self = pthread_self();
+	cb->__next = self->cancelbuf;
+	self->cancelbuf = cb;
+}
+
+void __pthread_do_unregister(struct __ptcb *cb)
+{
+	struct pthread *self = __pthread_self();
+	self->cancelbuf = self->cancelbuf->__next;
+}
+
 static int start(void *p)
 {
 	struct pthread *self = p;