Re: [naviserver-devel] strict aliasing?

[Stephen D. <sd...@gm...>]

On 6/11/05, Zoran Vasiljevic <zv...@ar...> wrote:
> Hi
>=20
> When you compile w/o debugging (i.e. with optimisation)
> the GCC spits whole-lotta stuff like that:
>=20
> tclthread.c:401: warning: dereferencing type-punned pointer will
> break strict-aliasing rules
> tclthread.c:401: warning: dereferencing type-punned pointer will
> break strict-aliasing rules
>=20
> The warning sems to trigger when a pointer is casted like this:
>=20
>      enum {
>          EAbsWaitIdx, EBroadcastIdx, ECreateIdx, EDestroyIdx, ESetIdx,
>          ESignalIdx, ETimedWaitIdx, EWaitIdx
>      } opt;
>=20
>      if (!GetArgs(interp, objc, objv, opts, 'e', ECreateIdx,
>                    (int *) &opt, (void **) &condPtr)) {
>          return TCL_ERROR;
>=20
> The "opt" and "condPtr" in GetArgs() are casted and it barks
> at them. I cannot possibly imagine changing all code to
> something like:
>=20
>      enum {
>          EAbsWaitIdx, EBroadcastIdx, ECreateIdx, EDestroyIdx, ESetIdx,
>          ESignalIdx, ETimedWaitIdx, EWaitIdx
>      } opt;
>      int myOpt =3D (int)opt;
>=20
>      if (!GetArgs(interp, objc, objv, opts, 'e', ECreateIdx,
>                    &myOpt, (void **) &condPtr)) {
>          return TCL_ERROR;
>=20
> This would mean lots of work and may introduce errors.
>=20
> I've read that you can use (starting with gcc 3.3) -fno-strict-aliasing
> which would remove those warnings. But also, somebody said that the
> effect of the "-O2" is gone in such cases (haven't be able to verify)
>=20
> What to do?
> Any ideas?


For much of the command parsing, I think something like this is fine:

    int opt;

    static CONST char *opts[] =3D {
        "cleanup", "list", "create", "put", "get", NULL
    };
    enum {
        CCleanupIdx, CListIdx, CCreateIdx, CPutIdx, CGetIdx
    };

    if (Tcl_GetIndexFromObj(interp, objv[1], opts, "option", 0, &opt)
!=3D TCL_OK) {
        return TCL_ERROR;
    }