zend_portability: Add ZEND_CONTAINER_OF()

[TimWolla]

Changes made with Coccinelle:

@@
type T_container;
identifier member;
expression e;
@@

- (T_container *)(((char *)(e)) - offsetof(T_container, member))
+ ZEND_CONTAINER_OF(e, T_container, member)

@@
type T_container;
identifier member;
expression e;
typedef uintptr_t;
@@

- (T_container *)(((uintptr_t)(e)) - offsetof(T_container, member))
+ ZEND_CONTAINER_OF(e, T_container, member)

@@
type T_container;
identifier member;
expression e;
@@

- (const T_container *)(((char *)(e)) - offsetof(T_container, member))
+ ZEND_CONTAINER_OF(e, T_container, member)

@@
type T_container;
identifier member;
expression e;
typedef uintptr_t;
@@

- (const T_container *)(((uintptr_t)(e)) - offsetof(T_container, member))
+ ZEND_CONTAINER_OF(e, T_container, member)

[iluuu1994]

Nit: This will discard const from ptr. With _Generic it would be possible to retain it. get_bcmath_number_from_obj() looks like the only relevant case, but also looks somewhat questionable. obj should not be const if we return a mutable pointer derived from it.

[SakiTakamachi]

get_bcmath_number_from_obj() simply seems to be my mistake.

[TimWolla]

get_bcmath_number_from_obj() simply seems to be my mistake.

Yes, that's a pre-existing bug.

With _Generic it would be possible to retain it.

Good idea, will look into that.

[ndossche]

I think this relies on UB (pointer arithmetic on NULL)

[TimWolla]

pointer arithmetic on NULL

That branch is never evaluated; it's also the “accepted” solution to define container_of() in a type-safe way without statement expressions. So of all possible UB, this seems to be reasonably safe.

[ndossche]

pointer arithmetic on NULL

That branch is never evaluated

This doesn't matter for UB.

it's also the “accepted” solution to define container_of() in a type-safe way without statement expressions.

The Linux kernel is compiled with various flags that makes various UB defined, so I'm not so sure this is a valid comparison.