Re: [PATCH 04/10] tools/libxl: Fix uninitialised variable in libxl__domain_get_device_model_uid()

[Ian Jackson <iwj@xenproject.org>]

Andrew Cooper writes ("[PATCH 04/10] tools/libxl: Fix uninitialised variable in libxl__domain_get_device_model_uid()"):
> The logic is sufficiently complicated I can't figure out if the complain is
> legitimate or not.  There is exactly one path wanting kill_by_uid set to true,
> so default it to false and drop the existing workaround for this problem at
> other optimisation levels.

The place where it's used is here:

    if (!rc && user) {
            state->dm_runas = user;
                    if (kill_by_uid)
                                state->dm_kill_uid = GCSPRINTF("%ld",...
        
This is gated by !rc.  So for this to be used uninitialised, we'd have
to get here with rc==0 but uninitialised kill_by_uid.

The label `out` is preceded by a nonzero assignment to rc.

All the `goto out` are preceded by either (i) nonzero assignment to
rc, or (ii) assignment to kill_by_uid and setting rc=0.

So the compiler is wrong.

If only we had sum types.

In the absence of sum types I suggest the following restructuring:
Change all the `rc = ERROR...; goto out;` to `goto err` and make `goto
out` be the success path only.

Ian.