Re: preprocessor/4976: cpp fails to warn about macro redefinitions

Re: preprocessor/4976: cpp fails to warn about macro redefinitions

[neil]

Synopsis: cpp fails to warn about macro redefinitions

State-Changed-From-To: open->closed
State-Changed-By: neil
State-Changed-When: Fri Nov 30 15:03:08 2001
State-Changed-Why:
    Please don't mark PRs as high priority; that is supposed to
    be reserved for GCC maintainers.
    
    GCC has been fixed to emit the warning in 3.0.3 and 3.1.
    3.0.2 only warns if -pedantic.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4976&database=gcc

Re: preprocessor/4976: cpp fails to warn about macro redefinitions

[neil]

The following reply was made to PR preprocessor/4976; it has been noted by GNATS.

From: neil@gcc.gnu.org
To: fredette@mit.edu, gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org,
  gcc-prs@gcc.gnu.org, nobody@gcc.gnu.org
Cc:  
Subject: Re: preprocessor/4976: cpp fails to warn about macro redefinitions
Date: 30 Nov 2001 23:03:09 -0000

 Synopsis: cpp fails to warn about macro redefinitions
 
 State-Changed-From-To: open->closed
 State-Changed-By: neil
 State-Changed-When: Fri Nov 30 15:03:08 2001
 State-Changed-Why:
     Please don't mark PRs as high priority; that is supposed to
     be reserved for GCC maintainers.
     
     GCC has been fixed to emit the warning in 3.0.3 and 3.1.
     3.0.2 only warns if -pedantic.
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4976&database=gcc

Re: preprocessor/4976: cpp fails to warn about macro redefinitions

[Neil Booth]

The following reply was made to PR preprocessor/4976; it has been noted by GNATS.

From: Neil Booth <neil@daikokuya.demon.co.uk>
To: fredette@mit.edu
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: preprocessor/4976: cpp fails to warn about macro redefinitions
Date: Fri, 30 Nov 2001 23:02:13 +0000

 fredette@mit.edu wrote:-
 
 > cpp fails to warn about macro redefinitions.
 
 It was changed to only warn if -pedantic, for a reason lost in the
 mists of time.
 
 > gcc/gcc/cppmacro.c revision 1.46 introduced the NODE_WARN flag, with  
 > this code at the end of the _cpp_create_definition function:
 > 
 >  if (! ustrncmp (node->name, DSC ("__STDC_")))  
 >    node->flags |= NODE_WARN;
 > 
 > It is this NODE_WARN flag that is supposed to trigger (through the 
 > warn_of_redefinition function) a warning when a macro is redefined.  
 > 
 > The test seems wrong - as ustrncmp behaves like strncmp, this test  
 > will fail for all macros other than __STDC__.  I.e., only a  
 > redefined __STDC__ macro node will happen to get this flag.
 
 No, it will warn for any macro beginning with __STDC_ since that
 namespace is reserved.
 
 > Further, gcc/gcc/cpplib.c revision 1.240, in the do_undef function,
 > replaced a check of NODE_BUILTIN with NODE_WARN.  Assuming 
 > that normal macros are supposed to be tagged with NODE_WARN,  
 > this check is also wrong, because it will cause a warning
 > whenever a normal macro is undefined.
 
 No, normal macros are not tagged NODE_WARN.  If you look more closely
 at the code, you'd observe that macros tagged NODE_WARN trigger
 warnings unconditionally when redefined or undefined.
 
 Further, you would notice that NODE_WARN macros are precisely those
 beginning with __STDC_ and builtins like __TIME__ and __LINE__.
 
 We don't want code like
 
 #define x some thing
 #define x    some /* Comment.  */ thing
 
 to give a warning; the standard explicitly permits such things.  If
 all macros were tagged NODE_WARN, then everything would warn and there
 would be no point in the warn_of_redefinition() function.
 
 What causes non-trivial redefinitions of normal macros to be ignored
 in your case is the check for -pedantic in warn_of_redefinition().
 That was removed last week, and GCC 3.0.3 and 3.1 will warn regardless
 of -pedantic.
 
 Neil.

preprocessor/4976: cpp fails to warn about macro redefinitions

[fredette]

>Number:         4976
>Category:       preprocessor
>Synopsis:       cpp fails to warn about macro redefinitions
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Nov 30 14:16:01 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     Matthew Fredette
>Release:        gcc-3.0.2
>Organization:
>Environment:
NetBSD the-gates-of-delirium.home 1.5W NetBSD 1.5W (THE-GATES-OF-DELIRIUM) #3: Fri Jul 13 09:31:17 EDT 2001     root@the-gates-of-delirium:/data/union-i386/src/sys/arch/i386/compile/THE-GATES-OF-DELIRIUM i386
>Description:
cpp fails to warn about macro redefinitions.

gcc/gcc/cppmacro.c revision 1.46 introduced the NODE_WARN flag, with  
this code at the end of the _cpp_create_definition function:

 if (! ustrncmp (node->name, DSC ("__STDC_")))  
   node->flags |= NODE_WARN;

It is this NODE_WARN flag that is supposed to trigger (through the 
warn_of_redefinition function) a warning when a macro is redefined.  

The test seems wrong - as ustrncmp behaves like strncmp, this test  
will fail for all macros other than __STDC__.  I.e., only a  
redefined __STDC__ macro node will happen to get this flag.

Further, gcc/gcc/cpplib.c revision 1.240, in the do_undef function,
replaced a check of NODE_BUILTIN with NODE_WARN.  Assuming 
that normal macros are supposed to be tagged with NODE_WARN,  
this check is also wrong, because it will cause a warning
whenever a normal macro is undefined.
>How-To-Repeat:
Try to preprocess a file that defines a macro, then redefines
it with a different value.
>Fix:
Remove the ! from the test at line 1426 of gcc/gcc/cppmacro.c, revision 1.87.
Replace NODE_WARN with NODE_BUILTIN at line 496 of gcc/gcc/gcclib.c, revision 1.287.
>Release-Note:
>Audit-Trail:
>Unformatted: