[Bug c/71152] New: NULL is not cast to (void *) as it ought to be if compiling code with -c

[rstrode at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71152

Bug ID: 71152
   Summary: NULL is not cast to (void *) as it ought to be if
compiling code with -c
   Product: gcc
   Version: 6.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
  Assignee: unassigned at gcc dot gnu.org
  Reporter: rstrode at redhat dot com
  Target Milestone: ---

Created attachment 38499
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38499&action=edit
small test case try compiling with -c and without

I was refactoring code in a project and moved some code off to a helper
function.
The helper function returns an integer error code and the main function returns
a pointer.

When I moved the error handling code over from the main function to the helper
function, I neglected to change the return code from NULL to -1.

gcc didn't warn about this.

So I wrote a quick test case (attached) and discovered something very strange.

gcc does warn if you compile and link the code in one step, i.e.:

$ gcc nulltest.c
nulltest.c: In function ‘NULL_as_int’:
nulltest.c:6:12: warning: return makes integer from pointer without a cast
[-Wint-conversion]
 return NULL;
^~~~
$ 


But if you pass -c to defer linking, the bug manifests:

$ gcc nulltest.c -c
$

[Bug c/71152] NULL is not cast to (void *) as it ought to be if compiling code with -c

[rstrode at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71152

--- Comment #1 from Ray Strode  ---
$ rpm -q gcc
gcc-6.0.0-0.20.fc25.x86_64

[Bug c/71152] NULL is not cast to (void *) as it ought to be if compiling code with -c

[rstrode at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71152

--- Comment #2 from Ray Strode  ---
this test case works as expected with gcc-5.3.1-6.fc23.x86_64

[Bug c/71152] NULL is not cast to (void *) as it ought to be if compiling code with -c

[rstrode at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71152

--- Comment #6 from Ray Strode  ---
i do indeed seem to have ccache installed, thanks.

[Bug c/65452] New: strcmp (foo, foo) could give a warning

[rstrode at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65452

Bug ID: 65452
   Summary: strcmp (foo, foo) could give a warning
   Product: gcc
   Version: unknown
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
  Assignee: unassigned at gcc dot gnu.org
  Reporter: rstrode at redhat dot com

Created attachment 35043
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35043&action=edit
example that could warn

sometimes gcc will give a warning like:

warning: the address of 'foo' will always evaluate as 'true'

if the address foo is used in a conditional expression.

It would be useful if there was also a warning of the form:

warning: the comparison of 'foo' with itself will always evaluate as 'true'

if the code does "if (strcmp (foo, foo) == 0)" or similar.

[Bug c/65452] strcmp (foo, foo) could give a warning

[rstrode at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65452

--- Comment #2 from Ray Strode  ---
probably should catch

if (foo == foo) {
}

type situations too.