Pretty sure it's safe! Take this program: typedef struct { int x; } Base; typedef struct { Base base; int y; } Derived;

Pretty sure it's safe! Take this program: typedef struct { int x; } Base; typedef struct { Base base; int y; } Derived; int f(Base* b, Derived* d) { b->x = 0; d->base.x = 1; return b->x; } Notice that if we are accessing the base members of "d", we are still accessing them through a struct of type "Base" (d->base.x). If we compile this with strict aliasing, you can see the output is allowing that the two might alias (while this isn't a proof, it's a strong indication that this is aliasing-correct). 0000000000000000 <f>: 0: c7 07 00 00 00 00 mov DWORD PTR [rdi],0x0 6: c7 06 01 00 00 00 mov DWORD PTR [rsi],0x1 c: 8b 07 mov eax,DWORD PTR [rdi] e: c3 ret