[PATCH] fixincludes: don't assume getcwd() can handle NULL argument

[Eric Gallager]

On Tue, Nov 9, 2021 at 8:50 AM Xi Ruoyao via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> POSIX says:
>
>     On some implementations, if buf is a null pointer, getcwd() may obtain
>     size bytes of memory using malloc(). In this case, the pointer returned
>     by getcwd() may be used as the argument in a subsequent call to free().
>     Invoking getcwd() with buf as a null pointer is not recommended in
>     conforming applications.
>
> This produces an error building GCC with --enable-werror-always:
>
>     ../../../fixincludes/fixincl.c: In function ‘process’:
>     ../../../fixincludes/fixincl.c:1356:7: error: argument 1 is null but
>     the corresponding size argument 2 value is 4096 [-Werror=nonnull]
>
> And, at least we've been leaking memory even if getcwd() supports this
> non-standard extension.
>
> fixincludes/ChangeLog:
>
>         * fixincl.c (process): Allocate and deallocate the buffer for
>           getcwd() explicitly.
> ---
>  fixincludes/fixincl.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fixincludes/fixincl.c b/fixincludes/fixincl.c
> index 6dba2f6e830..b4b1e38ede7 100644
> --- a/fixincludes/fixincl.c
> +++ b/fixincludes/fixincl.c
> @@ -1353,9 +1353,11 @@ process (void)
>    if (access (pz_curr_file, R_OK) != 0)
>      {
>        int erno = errno;
> +      char *buf = xmalloc (MAXPATHLEN);
>        fprintf (stderr, "Cannot access %s from %s\n\terror %d (%s)\n",
> -               pz_curr_file, getcwd ((char *) NULL, MAXPATHLEN),
> +               pz_curr_file, getcwd (buf, MAXPATHLEN),
>                 erno, xstrerror (erno));
> +      free (buf);
>        return;
>      }
>
> --
> 2.33.1

This seems to contradict bug 21823:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=21823
It would fix bug 80047, though:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80047