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

Xi Ruoyao xry111@mengyan1223.wang
Tue Nov 9 13:49:38 GMT 2021

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.


	* 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);

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