[XEN PATCH v2] domain: add ASSERT to help static analysis tools

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

Static analysis tools may detect a possible null pointer
dereference of 'config'. This ASSERT helps them in detecting
that such a condition is not possible given that only
real domains can enter this branch, which are guaranteeed to have
a non-NULL config at this point, but this information is not
inferred by the tool.

Checking that the condition given in the assertion holds via
testing is the means to protect release builds, where the assertion
expands to effectively nothing.

Suggested-by: Julien Grall <julien@xxxxxxx>
Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
Changes in v2:
- Clarified the context in which the assertion is useful.

The check may be later improved by proper error checking
instead of relying on the semantics explained here:
https://lore.kernel.org/xen-devel/61f04d4b-34d9-4fd1-a989-56b042b4f3d8@xxxxxxxxxx/
---
 xen/common/domain.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 8f9ab01c0cb7..924099db1098 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -700,6 +700,13 @@ struct domain *domain_create(domid_t domid,
 
     if ( !is_idle_domain(d) )
     {
+        /*
+         * The assertion helps static analysis tools infer that config cannot
+         * be NULL in this branch, which in turn means that it can be safely
+         * dereferenced. Therefore, this assertion is not redundant.
+         */
+        ASSERT(config);
+
         watchdog_domain_init(d);
         init_status |= INIT_watchdog;
 
-- 
2.34.1