Dave Korn wrote: > Ben Elliston wrote: >> This patch silences the following warnings when building libgcc: >> >> unwind-dw2-fde.c:321: warning: dereferencing type-punned pointer will break >> strict-aliasing rules > >> - const _Unwind_Ptr x_ptr = *(const _Unwind_Ptr *) x->pc_begin; >> - const _Unwind_Ptr y_ptr = *(const _Unwind_Ptr *) y->pc_begin; >> + _Unwind_Ptr x_ptr, y_ptr; >> + memcpy (&x_ptr, x->pc_begin, sizeof (_Unwind_Ptr)); >> + memcpy (&y_ptr, y->pc_begin, sizeof (_Unwind_Ptr)); > > Say, I've been in the habit in the past (GCC 3.x) of avoiding these warnings > by doing like: > >> - const _Unwind_Ptr x_ptr = *(const _Unwind_Ptr *) x->pc_begin; >> - const _Unwind_Ptr y_ptr = *(const _Unwind_Ptr *) y->pc_begin; >> + const _Unwind_Ptr x_ptr = *(const _Unwind_Ptr *) (void *) x->pc_begin; >> + const _Unwind_Ptr y_ptr = *(const _Unwind_Ptr *) (void *) y->pc_begin; > > ... which I see no longer works. Was that ever correct, or was I just losing > information during the cast-to-void that meant GCC just couldn't diagnose a > potential problem, but it was still there? I believed that casting through > void would make the result could-alias-anything, which I thought would prevent > any untoward consequences.
Casting via void* just shuts up a warning; the bad code is still there. But this case should be fine AFAICS, because pc_begin is char[]. I'm not sure why we get the warning. Andrew.
