[libvirt] [libvirt-python PATCHv2 06/44] Import gnulib's xalloc_oversized macro

[Doug Goldstein]

From: "Daniel P. Berrange" <berrange at redhat.com>

Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
---
 libvirt-override.c |  1 +
 libvirt-utils.h    | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/libvirt-override.c b/libvirt-override.c
index 5d36ec5..860d3ab 100644
--- a/libvirt-override.c
+++ b/libvirt-override.c
@@ -20,6 +20,7 @@
 #include <Python.h>
 #include <libvirt/libvirt.h>
 #include <libvirt/virterror.h>
+#include <stddef.h>
 #include "typewrappers.h"
 #include "build/libvirt.h"
 #include "libvirt-utils.h"
diff --git a/libvirt-utils.h b/libvirt-utils.h
index aed64e6..c1223fd 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__ */
-- 
1.8.3.2