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, 21 insertions, 0 deletions

diff --git a/util.c b/util.c
index be102e3..2125a67 100644
--- a/util.c
+++ b/util.c
@@ -482,3 +482,24 @@ int write_file(const char *path, const char *buf)
 	close(fd);
 	return len == 0 ? 0 : -1;
 }
+
+/**
+ * do_clone() - Wrapper of __clone2() for ia64, clone() for other architectures
+ * @fn:		Entry point for child
+ * @stack_area:	Stack area for child: we'll point callees to the middle of it
+ * @stack_size:	Total size of stack area, passed to callee divided by two
+ * @flags:	clone() system call flags
+ * @arg:	Argument to @fn
+ *
+ * Return: thread ID of child, -1 on failure
+ */
+int do_clone(int (*fn)(void *), char *stack_area, size_t stack_size, int flags,
+	     void *arg)
+{
+#ifdef __ia64__
+	return __clone2(fn, stack_area + stack_size / 2, stack_size / 2,
+			flags, arg);
+#else
+	return clone(fn, stack_area + stack_size / 2, flags, arg);
+#endif
+}