util, pasta: Add do_clone() wrapper around __clone2() and clone()

Spotted in Debian's buildd logs: on ia64, clone(2) is not available:
the glibc wrapper is named __clone2() and it takes, additionally,
the size of the stack area passed by the caller.

Add a do_clone() wrapper handling the different cases, and also
taking care of pointing the child's stack in the middle of the
allocated area: on PA-RISC (hppa), handled by clone(), the stack
grows up, and on ia64 the stack grows down, but the register backing
store grows up -- and I think it might be actually used here.

Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/util.h b/util.h
index 2d4e1ff..02b55a9 100644
--- a/util.h
+++ b/util.h
@@ -81,13 +81,15 @@
 	(((struct in_addr *)(a))->s_addr == ((struct in_addr *)b)->s_addr)
 
 #define NS_FN_STACK_SIZE	(RLIMIT_STACK_VAL * 1024 / 8)
+int do_clone(int (*fn)(void *), char *stack_area, size_t stack_size, int flags,
+	     void *arg);
 #define NS_CALL(fn, arg)						\
 	do {								\
 		char ns_fn_stack[NS_FN_STACK_SIZE];			\
 									\
-		clone((fn), ns_fn_stack + sizeof(ns_fn_stack) / 2,	\
-		      CLONE_VM | CLONE_VFORK | CLONE_FILES | SIGCHLD,	\
-		      (void *)(arg));					\
+		do_clone((fn), ns_fn_stack, sizeof(ns_fn_stack),	\
+			 CLONE_VM | CLONE_VFORK | CLONE_FILES | SIGCHLD,\
+			 (void *)(arg));				\
 	} while (0)
 
 #if __BYTE_ORDER == __BIG_ENDIAN