Import gnulib's xalloc_oversized macro

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/libvirt-utils.h b/libvirt-utils.h
index 65b9b3b..05c1135 100644
--- a/libvirt-utils.h
+++ b/libvirt-utils.h
@@ -28,4 +28,19 @@
 # define MIN(a,b) (((a) < (b)) ? (a) : (b))
 #endif
 
+/* Return 1 if an array of N objects, each of size S, cannot exist due
+   to size arithmetic overflow.  S must be positive and N must be
+   nonnegative.  This is a macro, not a function, so that it
+   works correctly even when SIZE_MAX < N.
+
+   By gnulib convention, SIZE_MAX represents overflow in size
+   calculations, so the conservative dividend to use here is
+   SIZE_MAX - 1, since SIZE_MAX might represent an overflowed value.
+   However, malloc (SIZE_MAX) fails on all known hosts where
+   sizeof (ptrdiff_t) <= sizeof (size_t), so do not bother to test for
+   exactly-SIZE_MAX allocations on such hosts; this avoids a test and
+   branch when S is known to be 1.  */
+#define xalloc_oversized(n, s) \
+    ((size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) < (n))
+
 #endif /* __LIBVIRT_UTILS_H__ */