Re: [PATCH 7/7] qobject atomics osdep: Make a few macros more hygienic

[Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>]

On 1/9/23 14:59, Cédric Le Goater wrote:
> On 8/31/23 16:30, Eric Blake wrote:
> > On Thu, Aug 31, 2023 at 03:25:46PM +0200, Markus Armbruster wrote:
> >
> > [This paragraph written last: Bear with my stream of consciousness
> > review below, where I end up duplicating some of the conslusions you
> > reached before the point where I saw where the patch was headed]
> >
> > > Variables declared in macros can shadow other variables.  Much of the
> > > time, this is harmless, e.g.:
> > >
> > >      #define 
> > > _FDT(exp)                                                  \
> > >          do 
> > > {                                                           \
> > >              int ret = 
> > > (exp);                                           \
> > >              if (ret < 0) 
> > > {                                             \
> > >                  error_report("error creating device tree: %s: %s",   \
> > >                          #exp, 
> > > fdt_strerror(ret));                      \
> > >                  
> > > exit(1);                                               \
> > >              
> > > }                                                          \
> > >          } while (0)
> > Which is why I've seen some projects require a strict namespace
> > separation: if all macro parameters and any identifiers declared in
> > macros use either a leading or a trailing _ (I prefer a trailing one,
> > to avoid risking conflicts with libc reserved namespace; but leading
> > is usually okay), and all other identifiers avoid that namespace, then
> > you will never have shadowing by calling a macro from normal code.
> I started fixing the _FDT() macro since it is quite noisy at compile.
> Same for qemu_fdt_setprop_cells(). So are we ok with names like 'ret_'
> and 'i_' ? I used a 'local_' prefix for now but I can change.
See 
https://lore.kernel.org/qemu-devel/20230831225607.30829-12-philmd@xxxxxxxxxx/