Sptr: avoided potentially undefined behaviour.archive/overlappingWriteUnion

In src/nxt_unit_sptr.h::nxt_unit_sptr_set() we are setting one member of
a union based on another member which cppcheck[0] flags as undefined
behaviour

src/nxt_unit_sptr.h:27:18: error: Overlapping read/write of union is undefined behavior [overlappingWriteUnion]
    sptr->offset = (uint8_t *) ptr - sptr->base;
                 ^

I think this warning is correct as I can't see where we are setting
sptr->base beforehand which I think would make this defined behaviour.

To avoid any doubts take a copy of sptr->base and then use that value in
the above.

[0]: https://cppcheck.sourceforge.io/

1 files changed, 4 insertions, 1 deletions

diff --git a/src/nxt_unit_sptr.h b/src/nxt_unit_sptr.h
index 314416e4..6d867a5e 100644
--- a/src/nxt_unit_sptr.h
+++ b/src/nxt_unit_sptr.h
@@ -24,7 +24,10 @@ union nxt_unit_sptr_u {
 static inline void
 nxt_unit_sptr_set(nxt_unit_sptr_t *sptr, void *ptr)
 {
-    sptr->offset = (uint8_t *) ptr - sptr->base;
+    const uint8_t  *base;
+
+    base = sptr->base;
+    sptr->offset = (uint8_t *) ptr - base;
 }