“dereferencing type-punned pointer will break strict-aliasing rules” warning

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In order:

  • Yes. GCC will assume that the pointers cannot alias. For instance, if you assign through one then read from the other, GCC may, as an optimisation, reorder the read and write – I have seen this happen in production code, and it is not pleasant to debug.

  • Several. You could use a union to represent the memory you need to reinterpret. You could use a reinterpret_cast. You could cast via char * at the point where you reinterpret the memory – char * are defined as being able to alias anything. You could use a type which has __attribute__((__may_alias__)). You could turn off the aliasing assumptions globally using -fno-strict-aliasing.

  • __attribute__((__may_alias__)) on the types used is probably the closest you can get to disabling the assumption for a particular section of code.

For your particular example, note that the size of an enum is ill defined; GCC generally uses the smallest integer size that can be used to represent it, so reinterpreting a pointer to an enum as an integer could leave you with uninitialised data bytes in the resulting integer. Don’t do that. Why not just cast to a suitably large integer type?

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