On 09/18/11 01:36, Bruno Haible wrote:
This patch protects the dup2() calls in gnulib.
This change has some problems with GNU Emacs, and I suspect there will
be similar problems with printf, close, etc. so let's try to get see
if we can fix these problems with dup2 first.
Emacs has a separate way of building on Windows, one that doesn't
involve gnulib's replacement functions and is not likely to involve
them any time in the near future. I expect that Emacs developers will
rather omit the files lib/msvc-inval.c, lib/msvc-inval.h, and
m4/msvc-inval.m4 as part of the Emacs distribution, as they're useless
baggage for Emacs. However, I can't achieve this omission by invoking
gnulib-tool --avoid=msvc-inval, because dup2.c now includes
msvc-inval.h unilaterally.
I'd like a solution where --avoid=msvc-inval works.
Here's one way to do it. In dup2.c:
#if MSVC_HACK_NEEDED
# include "msvc-inval.h"
#else
# define TRY_MSVC_INVAL if (1)
# define CATCH_MSVC_INVAL else
# define DONE_MSVC_INVAL
#endif
but this leads into the second problem, as discussed below.
> @@ -64,7 +78,18 @@
> if (fd == desired_fd)
> return fcntl (fd, F_GETFL) == -1 ? -1 : fd;
> # endif
> - result = dup2 (fd, desired_fd);
> +
> + TRY_MSVC_INVAL
> + {
> + result = dup2 (fd, desired_fd);
> + }
> + CATCH_MSVC_INVAL
> + {
> + result = -1;
> + errno = EBADF;
> + }
> + DONE_MSVC_INVAL
This style is unsatisfying, because it propagates MSVC workarounds
into the rest of gnulib. I suspect it won't scale well when used
throughout gnulib for other functions. I'd rather have a solution
that puts the MSVC workarounds in a separate place, where MSVC-aware
programmers can work on them, a place which people who don't know or
care about MSVC ports can omit and ignore.
I also have some qualms about C macros that expand to series of tokens
with unbalanced braces.
How about something like this instead? Have dup2.c look
something like this:
[existing includes]
#if HAVE_DUP2
# undef dup2
# if MSVC_HACK_NEEDED /* NEW */
# include "msvc-hack.h" /* NEW */
# endif /* NEW */
int rpl_dup2 (int fd, int desired_fd)
{
...
result = dup2 (fd, desired_fd);
...
}
and then "msvc-hack.h" can #define dup2 to do whatever it likes. This
way, the source code to lib/dup2.c needs a relatively small change
(the three lines marked "/* NEW */" above) and can be read by others
largely without worrying about MSVC hacks.
Perhaps you can think of a better approach, but I hope you get
the idea.
