[PATCH RFC] lib: extend ASSERT()

[Jan Beulich <jbeulich@xxxxxxxx>]

The increasing amount of constructs along the lines of

    if ( !condition )
    {
        ASSERT_UNREACHABLE();
        return;
    }

is not only longer than necessary, but also doesn't produce incident
specific console output (except for file name and line number). Allow
the intended effect to be achieved with ASSERT(), by giving it a second
parameter allowing specification of the action to take in release builds
in case an assertion would have triggered in a debug one. The example
above then becomes

    ASSERT(condition, return);

Make sure the condition will continue to not get evaluated when just a
single argument gets passed to ASSERT().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
RFC: The use of a control flow construct as a macro argument may be
     controversial.

--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -818,11 +818,7 @@ int xenmem_add_to_physmap(struct domain
     union add_to_physmap_extra extra = {};
     struct page_info *pages[16];
 
-    if ( !paging_mode_translate(d) )
-    {
-        ASSERT_UNREACHABLE();
-        return -EACCES;
-    }
+    ASSERT(paging_mode_translate(d), return -EACCES);
 
     if ( xatp->space == XENMAPSPACE_gmfn_foreign )
         extra.foreign_domid = DOMID_INVALID;
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -55,12 +55,14 @@
 #endif
 
 #ifndef NDEBUG
-#define ASSERT(p) \
+#define ASSERT(p, ...) \
     do { if ( unlikely(!(p)) ) assert_failed(#p); } while (0)
 #define ASSERT_UNREACHABLE() assert_failed("unreachable")
 #define debug_build() 1
 #else
-#define ASSERT(p) do { if ( 0 && (p) ) {} } while (0)
+#define ASSERT(p, alt...) do { \
+        if ( !count_args(alt) || unlikely(!(p)) ) { alt; } \
+    } while ( 0 )
 #define ASSERT_UNREACHABLE() do { } while (0)
 #define debug_build() 0
 #endif