On Fri, Sep 18, 2020 at 06:39:57PM -0400, Arvind Sankar wrote: > On Fri, Sep 18, 2020 at 02:18:20PM -0700, Linus Torvalds wrote: > > On Fri, Sep 18, 2020 at 2:00 PM Arvind Sankar <nivedita@xxxxxxxxxxxx> wrote: > > > > > > You could just assert that offsetof(typeof(s),flex) == sizeof(s), no? > > > > No, because the whole point is that I want that "sizeof(s)" to *WARN*. > > Ouch, offsetof() and sizeof() will give different results in the > presence of alignment padding. > > https://godbolt.org/z/rqnxTK We really should be using offsetof() then. It's harmless because we're currently overallocating, not underallocating. The test case I did was: struct s { int count; char *p[]; }; struct_size(&s, p, 5); (48 bytes) struct_size2(&s, p, 5); (also 48 bytes) struct_size2 uses offsetof instead of sizeof. Your case is different because the chars fit in the padding at the end of the struct.
