Bug 22809 – ImportC: druntime’s definition of __builtin_offsetof leads to dereference of invalid pointer.

This C code, using the importc.h from druntime: typedef unsigned long size_t; #include "../druntime/import/importc.h" struct Foo { int x; }; int y = __builtin_offsetof(struct Foo, x); _Static_assert(__builtin_offsetof(struct Foo, x)==0, ""); Expands to: // off.i typedef unsigned long size_t; struct Foo { int x; }; int y = ((size_t)((char *)&((struct Foo *)0)->x - (char *)0)); // Error: dereference of invalid pointer `cast(Foo*)0LU` Static_assert(((size_t)((char *)&((struct Foo *)0)->x - (char *)0))==0, “”); Which fails to compile. Additionally, that C code fails to compile with clang, which complains: off.c:8:16: error: static_assert expression is not an integral constant expression _Static_assert(__builtin_offsetof(struct Foo, x)==0, ""); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ./../druntime/import/importc.h:50:33: note: expanded from macro '__builtin_offsetof' #define __builtin_offsetof(t,i) ((size_t)((char *)&((t *)0)->i - (char *)0)) ^ off.c:8:47: note: cannot access field of null pointer _Static_assert(__builtin_offsetof(struct Foo, x)==0, ""); ^ 1 error generated.

@WalterBright created dlang/dmd pull request #13736 "fix Issue 22809 - ImportC: druntime.s definition of __builtin_offseto…" fixing this issue: - fix Issue 22809 - ImportC: druntime.s definition of __builtin_offsetof leads to dereference of invalid pointer https://github.com/dlang/dmd/pull/13736

dlang/dmd pull request #13736 "fix Issue 22809 - ImportC: druntime.s definition of __builtin_offseto…" was merged into master: - 6a451a314256b94599692a6118e6679ebfcceba5 by Walter Bright: fix Issue 22809 - ImportC: druntime.s definition of __builtin_offsetof leads to dereference of invalid pointer https://github.com/dlang/dmd/pull/13736