Re: [Tinycc-devel] designated inits with duplicate fields

[grischka]

If you think it's okay and don't get responses, you might just give
it a try and push on mob.  Read more at
    http://repo.or.cz/w/tinycc.git

Thanks,

--- grischka

Guillaume Chéreau wrote:
> Hello,
>
> I found an issue with tcc.
> when trying to compile a code like this one:
>
>     struct {
>         int x;
>     } var = {
>         .x = 1,
>         .x = 2,
>     };
>
> tcc would not generate any error or warning about the duplicated field.
> Then at execution the value of var.x would be 3 (which happens to be
> the result of the binary OR applied to the two values).
>
> I think tcc should do like gcc in that case and consider that the last
> specified value is the correct one.
>
> The reason why this can be useful is because then we can use a macro
> that defines the list of default values to put into a structure field.
>  e.g:
>
>     #define DEFAULT_VALUES .x = 10, .y = 20
>     struct my_struct var = {DEFAULT_VALUES, .x = 5};
>
> I am not familiar with the code of tcc, so maybe there are better ways
> of fixing the issue, but I could get the behaviour I wanted by doing
> this change to the code :
>
> diff --git a/tccgen.c b/tccgen.c
> index 71d0809..2edf984 100644
> --- a/tccgen.c
> +++ b/tccgen.c
> @@ -4875,9 +4875,11 @@ static void init_putv(CType *type, Section
> *sec, unsigned long c,
>          case VT_BOOL:
>              vtop->c.i = (vtop->c.i != 0);
>          case VT_BYTE:
> +            *(char *)ptr &= ~(bit_mask << bit_pos);
>              *(char *)ptr |= (vtop->c.i & bit_mask) << bit_pos;
>              break;
>          case VT_SHORT:
> +            *(short *)ptr &= ~(bit_mask << bit_pos);
>              *(short *)ptr |= (vtop->c.i & bit_mask) << bit_pos;
>              break;
>          case VT_DOUBLE:
> @@ -4887,12 +4889,14 @@ static void init_putv(CType *type, Section
> *sec, unsigned long c,
>              *(long double *)ptr = vtop->c.ld;
>              break;
>          case VT_LLONG:
> +            *(long long *)ptr &= ~(bit_mask << bit_pos);
>              *(long long *)ptr |= (vtop->c.ll & bit_mask) << bit_pos;
>              break;
>          default:
>              if (vtop->r & VT_SYM) {
>                  greloc(sec, vtop->sym, c, R_DATA_PTR);
>              }
> +            *(int *)ptr &= ~(bit_mask << bit_pos);
>              *(int *)ptr |= (vtop->c.i & bit_mask) << bit_pos;
>              break;
>          }