Question: Violation of Strict Aliasing Rule ?

When a new sbs is created (as a char array) it is casted to struct type pointer, ex. SDS_HDR(8,s);. Isn't this violating the strict aliasing rule?
(Dereferencing a pointer that aliases an object that is not of a compatible type or one of the other types allowed by C 2011 6.5 paragraph 71 is undefined behavior)

Example:

```
sh = s_malloc(hdrlen+initlen+1);
...
s = (char*)sh+hdrlen;
...
SDS_HDR_VAR(8,s);
sh->len = initlen;
sh->alloc = initlen;
```
`#define SDS_HDR_VAR(T,s) struct sdshdr##T *sh = (void*)((s)-(sizeof(struct sdshdr##T)));`
`#define SDS_HDR(T,s) ((struct sdshdr##T *)((s)-(sizeof(struct sdshdr##T))))`