Re: [PATCH 0/4] use xmalloc in more places

[Jeff King <peff@peff.net>]

On Thu, Apr 11, 2019 at 12:43:08PM -0700, Taylor Blau wrote:

> > I don't think we can ban malloc, since we have to use it ourselves. :)
> >
> > With some contortions, we probably could unban it specifically in
> > wrapper.c (though note there are a few other calls I've left which would
> > need to be handled somehow).
> 
> Right. I think that I should have made this point clearer in my initial
> reply. I was thinking that we could #undef the banned macro in
> wrapper.c, or some similar hula-hooping.

That _probably_ works, but I think technically falls afoul of platforms
on which there's a malloc macro in the first place. We need to not just
#undef it then, but restore the original macro, which is impossible. So
you're better off just not fudging it in the first place. Which would
probably be something like:

  #define SUPPRESS_BAN_MALLOC
  #include "git-compat-util.h"

or something, with the appropriate magic in banned.h.

This might be academic, but you wouldn't know until somebody's platform
subtly breaks. ;) We did run into it already with strcpy(), I think,
hence the defensive #undefs in banned.h.

> Yeah... maybe that's the bigger question that I hadn't asked. I made the
> suggestion thinking that it would help newcomers avoid writing
> 'malloc()' and sending it if they didn't know we use our 'xmalloc()'
> instead.
> 
> But I'm not sure if the argument holds up. I think that in general
> exactly the sorts of new-comers that I'm thinking of would have more
> than one review cycle anyway, so it might not be worth the effort,
> anyway...

I think it's still a reasonable thought, even if I'm not sure the
balance of cost/reward is quite there so far (but might change if it's
an error we see people start to make). Compared to coccinelle, the
banned-function approach is a little nicer for helping new submitters
because it catches the problem during a normal compile (and we know
nobody would ever submit a patch without having at least compiled it,
right? ;) ).

-Peff