https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101832
--- Comment #11 from qinzhao at gcc dot gnu.org --- > (In reply to Jakub Jelinek from comment #3) > > This is intentional, if you embed an aggregate with flex array into another > > struct and ask not to cross the field boundaries (i.e. bos1), then the size > > of that field is exactly what is the maximum size. > > As we discussed in PR 107952 > (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107952): > > GCC extension accepts the following two cases: > > **Case 1: > > struct A { char data[1]; }; > struct B { int n; struct A a; }; > > as if the a.data[] array is a flex-array. > > **Case 2: > > struct C { int n; struct A a; int x; }; > > as if a.data[] can be up to 4 elements. > > So, what's you mean by "not to cross the field boundaries" is for the above > Case 2? > For Case 1, we should treat A.data as flexible array, and then B.A as a > structure that has flexible array, therefore B.A's size is flexible too. > > Is my understanding correct? After discussion, the following patch to clarify the above two cases was approved: https://gcc.gnu.org/pipermail/gcc-patches/2023-May/620122.html with this clarification, the above case 1 is accepted as a GCC extension, but case 2 will be deprecated. a warning option -Wflex-array-member-not-at-end is provided to detect case 2 in the user code. please see also PR77650.
