[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299 Marek Polacek mpolacek at gcc dot gnu.org changed: What|Removed |Added Status|WAITING |RESOLVED CC||mpolacek at gcc dot gnu.org Resolution|--- |FIXED --- Comment #13 from Marek Polacek mpolacek at gcc dot gnu.org --- So fixed.
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299 --- Comment #12 from Joseph S. Myers jsm28 at gcc dot gnu.org 2011-04-01 19:36:27 UTC --- Author: jsm28 Date: Fri Apr 1 19:36:23 2011 New Revision: 171850 URL: http://gcc.gnu.org/viewcvs?root=gccview=revrev=171850 Log: 2011-04-01 Vincent Lefevre vincent+...@vinc17.org PR c/36299 * gcc.dg/Waddress.c: New test. Added: trunk/gcc/testsuite/gcc.dg/Waddress.c Modified: trunk/gcc/testsuite/ChangeLog
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299 --- Comment #11 from Vincent Lefèvre vincent-gcc at vinc17 dot net 2011-03-11 15:15:16 UTC --- (In reply to comment #10) If you don't want this warning, please contribute a testcase to gcc-patc...@gcc.gnu.org, so this warning won't reappear in the future: Done: http://gcc.gnu.org/ml/gcc-patches/2011-03/msg00624.html
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299 --- Comment #8 from Manuel López-Ibáñez manu at gcc dot gnu.org 2011-03-02 10:51:51 UTC --- (In reply to comment #7) (In reply to comment #6) I think the intention is to warn, at least for a == (void *)0, since the address of a cannot be zero or null. So I would say that this is a regression. But this is valid in C, and in practice, such a test can occur in macro expansions: a macro can check whether some pointer is null before doing something with it. There shouldn't be a warning in such a case. Every warning warns about something valid in C, otherwise it would be an error not a warning.
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299
--- Comment #9 from Vincent Lefèvre vincent at vinc17 dot org 2011-03-02
15:17:33 UTC ---
(In reply to comment #8)
Every warning warns about something valid in C, otherwise it would be an error
not a warning.
No, for instance:
int main(void)
{
int i;
return i;
}
This is undefined behavior and detected by GCC, but one gets only a warning:
tst.c: In function ‘main’:
tst.c:4: warning: ‘i’ is used uninitialized in this function
Compare to a == 0 in the above testcase, which has a well-defined behavior.
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299 Manuel López-Ibáñez manu at gcc dot gnu.org changed: What|Removed |Added Status|UNCONFIRMED |WAITING Last reconfirmed||2011.03.02 17:06:47 Ever Confirmed|0 |1 --- Comment #10 from Manuel López-Ibáñez manu at gcc dot gnu.org 2011-03-02 17:06:47 UTC --- (In reply to comment #9) This is undefined behavior and detected by GCC, but one gets only a warning: I am not going to waste time discussing the fine-points of what is a valid C program. If you don't want this warning, please contribute a testcase to gcc-patc...@gcc.gnu.org, so this warning won't reappear in the future: http://gcc.gnu.org/wiki/HowToPrepareATestcase Otherwise, someone will come who thinks that this should be warned and they will fix it.
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299 --- Comment #4 from Manuel López-Ibáñez manu at gcc dot gnu.org 2011-03-01 09:14:27 UTC --- (In reply to comment #3) The documentation should be improved anyway (the word suspicious is very subjective). Please propose a patch. You should be able to work-around the macro case by casting the array to (char *) or perhaps casting to (void *) ? Yes, this makes sense. Perhaps this should be documented. Is it working? I meant to say ideally one should be able to do this but I don't think it is working right now (and probably there are not testcases testing this). How about something like __extension__, e.g. __no_warnings__ would disable the warnings for the following statement or expression? If expression, one could There was a patch floating around in gcc-patches to implement that but since GCC location info is far from perfect (especially on macro expansions), I think it won't work well in practice. Moreover, the preferred way is to use the existing diagnostic pragmas. http://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299 --- Comment #5 from Vincent Lefèvre vincent at vinc17 dot org 2011-03-01 15:05:19 UTC --- Under Debian, I can no longer reproduce the problem with GCC 4.5.2: $ gcc-4.5 -Wall warn-nulladdress.c $ gcc-4.5 -Waddress warn-nulladdress.c $ gcc-4.4 -Wall warn-nulladdress.c warn-nulladdress.c: In function ‘main’: warn-nulladdress.c:14: warning: the address of ‘a’ will never be NULL $ gcc-4.4 -Waddress warn-nulladdress.c warn-nulladdress.c: In function ‘main’: warn-nulladdress.c:14: warning: the address of ‘a’ will never be NULL So, I assume that it has been fixed anyway. Do you confirm?
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299 --- Comment #6 from Manuel López-Ibáñez manu at gcc dot gnu.org 2011-03-01 15:37:25 UTC --- (In reply to comment #5) So, I assume that it has been fixed anyway. Do you confirm? I think the intention is to warn, at least for a == (void *)0, since the address of a cannot be zero or null. So I would say that this is a regression.
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299 --- Comment #7 from Vincent Lefèvre vincent at vinc17 dot org 2011-03-02 01:15:23 UTC --- (In reply to comment #6) I think the intention is to warn, at least for a == (void *)0, since the address of a cannot be zero or null. So I would say that this is a regression. But this is valid in C, and in practice, such a test can occur in macro expansions: a macro can check whether some pointer is null before doing something with it. There shouldn't be a warning in such a case.
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
--- Comment #2 from manu at gcc dot gnu dot org 2008-08-23 12:53 --- Andrew, how could we detect that it is a decayed array? I think we would like to warn for if (a == (void *) 0) but not for if ((void *)a == 0) or even if possible not for if (a[0] == 0) Vincent, this warning was added on purpose, because probably someone requested it. I don't see that it is very different from the documented case of using the address of a function in a conditional. You should be able to work-around the macro case by casting the array to (char *) or perhaps casting to (void *) ? That said, we would like to not warn within macros for a wide range of warnings but we don't have the infrastructure to do that yet. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
--- Comment #3 from vincent at vinc17 dot org 2008-08-23 20:00 ---
(In reply to comment #2)
this warning was added on purpose, because probably someone requested it. I
don't see that it is very different from the documented case of using the
address of a function in a conditional.
The documentation should be improved anyway (the word suspicious is very
subjective).
You should be able to work-around the macro case by casting the array to (char
*) or perhaps casting to (void *) ?
Yes, this makes sense. Perhaps this should be documented.
That said, we would like to not warn within
macros for a wide range of warnings but we don't have the infrastructure to do
that yet.
How about something like __extension__, e.g. __no_warnings__ would disable the
warnings for the following statement or expression? If expression, one could
still use __no_warnings__ with ({ ... }). Keywords for individual warnings or
warning groups would even be better. At the same time, it would be nice to have
some macro defined, declaring that such a keyword is available (that would be
much better than testing the GCC version).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299
[Bug c/36299] spurious and undocumented warning with -Waddress for a == 0 when a is an array
--- Comment #1 from pinskia at gcc dot gnu dot org 2008-05-22 20:00 --- if (a == 0) return 1; else if (a == (void *) 0) Those two should warn about being address being zero. a decays to a pointer type and really a[0]. -- Pinski -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36299
