MINOR: debug: add a new DISGUISE() macro to pass a value as identity

This does exactly the same as ALREADY_CHECKED() but does it inline,
returning an identical copy of the scalar variable without letting
the compiler know how it might have been transformed. This can
forcefully disable certain null-pointer checks or result checks when
known undesirable. Typically forcing a crash with *(DISGUISE(NULL))=0
will not cause a null-deref warning.

diff --git a/include/common/compiler.h b/include/common/compiler.h
index 7b086e310c454e034023a9d4ffa0a2d61924ad49..5578a58bc50084b2f5a5594bd9bb62650b6664c4 100644 (file)
--- a/include/common/compiler.h
+++ b/include/common/compiler.h
@@ -77,6 +77,11 @@
  */
 #define ALREADY_CHECKED(p) do { asm("" : "=rm"(p) : "0"(p)); } while (0)
 
+/* same as above but to be used to pass the input value to the output but
+ * without letting the compiler know about its initial properties.
+ */
+#define DISGUISE(v) ({ typeof(v) __v = (v); ALREADY_CHECKED(__v); __v; })
+
 /*
  * Gcc >= 3 provides the ability for the program to give hints to the
  * compiler about what branch of an if is most likely to be taken. This