On Sun, Sep 13, 2020 at 10:32:27AM +0200, Bruno Haible wrote:
> > The prompt parameter to getpass() is declared as nonnull (using a GCC
> > nonnull attribute), but the implementation checks whether it is null in
> > two places. GCC warns about this. This commit removes the checks
>
> GCC warnings ought to help us make the code more robust. Removing the
> NULL check makes it less robust.
>
> The problem has already occurred a couple of times:
> https://lists.gnu.org/archive/html/bug-gnulib/2020-01/msg00050.html
> https://lists.gnu.org/archive/html/bug-gnulib/2018-08/msg00116.html
> https://lists.gnu.org/archive/html/bug-gnulib/2013-02/msg00060.html
> https://lists.gnu.org/archive/html/bug-gnulib/2009-12/msg00173.html
>
> I would prefer that the same idiom gets used, that gets rid of the
> warning without removing the NULL check at run time.
Thanks.
It is a little complicated because there are three implementations of
getpass(), and two of them do not check the prompt:
* The glibc implementation passes the prompt as %s to fprintf(). I
guess that glibc will generally print "(null)", although I've seen
GCC "optimize" similar things to fputs() in the past, which will
dereference null. I guess I won't worry about it.
* The POSIX implementation in gnulib passes the prompt to fputs()
without checking for null. I guess we should fix it.
I like the trick from one of your references about defining
_GL_ARG_NONNULL to empty. That works OK here.
So, how about like this?
-8<--------------------------cut here-------------------------->8--
From: Ben Pfaff <b...@cs.stanford.edu>
Date: Sat, 12 Sep 2020 15:54:36 -0700
Subject: [PATCH] getpass: Check for nonnull prompt argument while avoiding
warnings.
The prompt parameter to getpass() is declared as nonnull (using a GCC
nonnull attribute). Gnulib contains two implementations of this function,
one for POSIX, one for Windows. The Windows implementation checked for
a nonnull prompt, which caused a GCC warning. This commit fixes that by
avoiding the nonnull attribute when building getpass.c. The POSIX
implementation did not check for a nonnull prompt. This commit increases
the robustness by adding such a check.
2020-09-12 Ben Pfaff <b...@cs.stanford.edu>
Check for nonnull prompt argument while avoiding warnings.
* lib/getpass.c (_GL_ARG_NONNULL): Define to empty.
(getpass) [!_WIN32]: Print prompt only if nonnull.
Use __builtin_signbit* with clang.
diff --git a/lib/getpass.c b/lib/getpass.c
index 3b0552ec58..ca528fdc09 100644
--- a/lib/getpass.c
+++ b/lib/getpass.c
@@ -16,6 +16,9 @@
with this program; if not, see <https://www.gnu.org/licenses/>. */
#ifndef _LIBC
+/* Don't use __attribute__ __nonnull__ in this compilation unit. Otherwise gcc
+ warns for the null checks on 'prompt' below. */
+# define _GL_ARG_NONNULL(params)
# include <config.h>
#endif
@@ -124,9 +127,12 @@ getpass (const char *prompt)
}
# endif
- /* Write the prompt. */
- fputs_unlocked (prompt, out);
- fflush_unlocked (out);
+ if (prompt)
+ {
+ /* Write the prompt. */
+ fputs_unlocked (prompt, out);
+ fflush_unlocked (out);
+ }
/* Read the password. */
nread = getline (&buf, &bufsize, in);
--
2.28.0
