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* Re: [PATCH][RFC] -Wno-... option to suppress builtin macro redefined    warnings
@ 2008-08-22 16:53 Simon Baldwin
  0 siblings, 0 replies; 16+ messages in thread
From: Simon Baldwin @ 2008-08-22 16:53 UTC (permalink / raw)
  To: gcc-patches; +Cc: Tom Tromey

Simon Baldwin wrote:
> Simon Baldwin wrote:
>> Tom Tromey wrote:
>>>>>>>> "Simon" == Simon Baldwin <simonb@google.com> writes:
>>>>>>>>             
>>>
>>> ...
>>> However, it seems to me that we would want to allow redefinition of
>>> some macros (__TIME__ et al) but not others (e.g., __LINE__).
>>>
>>> So, how about splitting builtin_array into two pieces (and just FYI,
>>> there's a comment above referring to "two tables" that should be
>>> changed) and then unconditionally setting NODE_WARN for one table but
>>> not the other?  Or, just adding a special case in the builtin
>>> definition loop for the BT_* constants we care to allow.
>>>   
>>
>> Thank you for the note.
>>
>> I guess that in general it just seems more, um, seamless to either 
>> allow or disallow any builtin macro to be redefined.  It means that 
>> there's no "is it redefinable or not?" decision to be made when new 
>> builtins are added.  It also neatly sidesteps the issue of then 
>> having to document which builtins are redefinable and which aren't 
>> (also no update to this doc should new builtins be added), or having 
>> to deal with requests to move builtins between redefinable/fixed 
>> groups.  In other words, the lowest impact on future code maintainers 
>> consistent with low impact on current code.
>>
>> Granted, somebody could well redefine __LINE__ or similar and make a 
>> mess of compilation, but there are of course plenty of other ways to 
>> make a mess of compilation with other gcc flags.  
>> -Wno-builtin-macro-redefined is aimed at the control-freak automated 
>> build system rather than the casual user, so it seemed okay, to me 
>> anyway, for it to bear closer resemblance to a chainsaw than to a 
>> scalpel.
>>
>> That said, I'm not wildly opposed to creating two "classes" of 
>> builtin.  It just seems like doing so might sow slightly more 
>> confusion than it prevents.
>
> Tom, any further thoughts on this?
>
> It's certainly not hard to split built-in macros into two tiers, those 
> where redefinition warning can be suppressed by providing 
> -Wno-builtin-macro-redefined, and those where it can't.  However, 
> since it's all just about suppressing a warning, it may be that one 
> policy to cover all of them will suffice, and be simpler to manage and 
> maintain.
>
> Thanks.
>


No response from Tom to date.

Would anyone else be prepared to pick this up in the interim?  Thanks.

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^ permalink raw reply	[flat|nested] 16+ messages in thread
* [PATCH][RFC] -Wno-... option to suppress builtin macro redefined warnings
@ 2008-07-30 15:12 Simon Baldwin
  2008-07-30 15:27 ` Joseph S. Myers
  2008-08-08 16:01 ` Tom Tromey
  0 siblings, 2 replies; 16+ messages in thread
From: Simon Baldwin @ 2008-07-30 15:12 UTC (permalink / raw)
  To: gcc-patches

This patch adds a warning suppression flag, -Wno-builtin-macro-redefined,
to silence gcc warnings where builtin macros such as __TIME__ are undefined
or redefined, either on the command line or by directives.

This change permits a tightly controlled build system, one that uses
'-Werror', to redefine __TIME__, __DATE__, __TIMESTAMP__ and so on without
raising compilation errors.  As a result, such a system can generate object
files from code, containing date and time macros, that will be bitwise equal
to object files built from the same code, no matter when compiled.

Once redefined, a builtin macro is no longer builtin, and so becomes subject
to the usual warnings for redefinition (for example, if set to X, it may
only be reset to X without warning if not undefined explicitly first).

Tested and confirmed for C and C++ with testsuite and bootstrap.

Thoughts, comments, suggestions?  Aimed at trunk.  Thanks.


libcpp/ChangeLog:
2008-07-30  Simon Baldwin  <simonb@google.com>

	* include/cpplib.h (struct cpp_options): Added new boolean flag
	warn_builtin_macro_redefined.
	* init.c (cpp_create_reader): Initialize warn_builtin_macro_redefined.
	* (cpp_init_special_builtins): Add NODE_WARN to builtins only if
	warn_builtin_macro_redefined.
	* macro.c (warn_of_redefinition): Return false if a builtin macro
	is not flagged with NODE_WARN.

gcc/ChangeLog:
2008-07-30  Simon Baldwin  <simonb@google.com>

	* c-opts.c (c_common_handle_option): Added handling for
	-Wbuiltin-macro-redefined command line option.
	* c.opt: Added builtin-macro-redefined option.
	* doc/invoke.texi (Warning Options): Added -Wbuiltin-macro-redefined
	documentation.

gcc/testsuite/ChangeLog:
2008-07-30  Simon Baldwin  <simonb@google.com>

	* gcc.dg/builtin-redefine.c: New.


Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi	(revision 138245)
+++ gcc/doc/invoke.texi	(working copy)
@@ -228,7 +228,8 @@ Objective-C and Objective-C++ Dialects}.
 @xref{Warning Options,,Options to Request or Suppress Warnings}.
 @gccoptlist{-fsyntax-only  -pedantic  -pedantic-errors @gol
 -w  -Wextra  -Wall  -Waddress  -Waggregate-return  -Warray-bounds @gol
--Wno-attributes -Wc++-compat -Wc++0x-compat -Wcast-align  -Wcast-qual  @gol
+-Wno-attributes -Wno-builtin-macro-redefined @gol
+-Wc++-compat -Wc++0x-compat -Wcast-align  -Wcast-qual  @gol
 -Wchar-subscripts -Wclobbered  -Wcomment @gol
 -Wconversion  -Wcoverage-mismatch  -Wno-deprecated  @gol
 -Wno-deprecated-declarations -Wdisabled-optimization  @gol
@@ -3720,6 +3721,11 @@ unrecognized attributes, function attrib
 etc.  This will not stop errors for incorrect use of supported
 attributes.
 
+@item -Wno-builtin-macro-redefined
+@opindex Wno-builtin-macro-redefined
+@opindex Wbuiltin-macro-redefined
+Do not warn if a builtin macro, such as @code{__TIME__}, is redefined.
+
 @item -Wstrict-prototypes @r{(C and Objective-C only)}
 @opindex Wstrict-prototypes
 @opindex Wno-strict-prototypes
Index: gcc/testsuite/gcc.dg/builtin-redefine.c
===================================================================
--- gcc/testsuite/gcc.dg/builtin-redefine.c	(revision 0)
+++ gcc/testsuite/gcc.dg/builtin-redefine.c	(revision 0)
@@ -0,0 +1,51 @@
+/* Test -Wno-builtin-macro-redefined warnings.  */
+
+/* { dg-do compile } */
+/* { dg-options "-Wno-builtin-macro-redefined -U__DATE__ -D__TIME__=X" } */
+
+#if defined(__DATE__)
+#error "-U error: __DATE__ is defined, but should not be"
+#endif
+
+#if __TIME__ != X
+#error "-D error: __TIME__ is not defined as expected"
+#endif
+
+#if !defined(__TIMESTAMP__)
+#error "Builtin macro error: __TIMESTAMP__ is not defined"
+#endif
+
+
+#undef __TIME__              /* Undefine while defined.  */
+#undef __TIME__              /* Undefine while already undefined.  */
+
+#define __TIME__ "X"         /* Define while undefined.  */
+#define __TIME__ "X"         /* Re-define while defined.  */
+
+#define __TIME__ "Y"         /* { dg-warning "\"__TIME__\" redefined" } */
+/* { dg-warning "previous definition" "" { target *-*-* } 23 } */
+
+#undef __TIME__              /* Undefine while defined.  */
+
+
+#undef __DATE__              /* Undefine while already undefined.  */
+
+#define __DATE__ "X"         /* Define while undefined.  */
+#define __DATE__ "X"         /* Re-define while defined.  */
+
+#define __DATE__ "Y"         /* { dg-warning "\"__DATE__\" redefined" } */
+/* { dg-warning "previous definition" "" { target *-*-* } 34 } */
+
+#undef __DATE__              /* Undefine while defined.  */
+
+
+#define __TIMESTAMP__ "X"    /* Define while undefined.  */
+#define __TIMESTAMP__ "X"    /* Re-define while defined.  */
+
+#define __TIMESTAMP__ "Y"    /* { dg-warning "\"__TIMESTAMP__\" redefined" } */
+/* { dg-warning "previous definition" "" { target *-*-* } 43 } */
+
+#undef __TIMESTAMP__         /* Undefine while defined.  */
+
+
+int unused;  /* Silence `ISO C forbids an empty translation unit' warning.  */
Index: gcc/c.opt
===================================================================
--- gcc/c.opt	(revision 138245)
+++ gcc/c.opt	(working copy)
@@ -131,6 +131,10 @@ Wbad-function-cast
 C ObjC Var(warn_bad_function_cast) Warning
 Warn about casting functions to incompatible types
 
+Wbuiltin-macro-redefined
+C ObjC C++ ObjC++ Warning
+Warn when a builtin preprocessor macro is undefined or redefined
+
 Wc++-compat
 C ObjC Var(warn_cxx_compat) Warning
 Warn about C constructs that are not in the common subset of C and C++
Index: gcc/c-opts.c
===================================================================
--- gcc/c-opts.c	(revision 138245)
+++ gcc/c-opts.c	(working copy)
@@ -423,6 +423,10 @@ c_common_handle_option (size_t scode, co
 	warn_pointer_sign = 1;
       break;
 
+    case OPT_Wbuiltin_macro_redefined:
+      cpp_opts->warn_builtin_macro_redefined = value;
+      break;
+
     case OPT_Wcomment:
     case OPT_Wcomments:
       cpp_opts->warn_comments = value;
Index: libcpp/macro.c
===================================================================
--- libcpp/macro.c	(revision 138245)
+++ libcpp/macro.c	(working copy)
@@ -1392,6 +1392,10 @@ warn_of_redefinition (cpp_reader *pfile,
   if (node->flags & NODE_WARN)
     return true;
 
+  /* Suppress warnings for builtins that lack the NODE_WARN flag.  */
+  if (node->flags & NODE_BUILTIN)
+    return false;
+
   /* Redefinitions of conditional (context-sensitive) macros, on
      the other hand, must be allowed silently.  */
   if (node->flags & NODE_CONDITIONAL)
Index: libcpp/include/cpplib.h
===================================================================
--- libcpp/include/cpplib.h	(revision 138245)
+++ libcpp/include/cpplib.h	(working copy)
@@ -349,6 +349,10 @@ struct cpp_options
      Presumably the usage is protected by the appropriate #ifdef.  */
   unsigned char warn_variadic_macros;
 
+  /* Nonzero means warn about builtin macros that are redefined or
+     explicitly undefined.  */
+  unsigned char warn_builtin_macro_redefined;
+
   /* Nonzero means turn warnings into errors.  */
   unsigned char warnings_are_errors;
 
Index: libcpp/init.c
===================================================================
--- libcpp/init.c	(revision 138245)
+++ libcpp/init.c	(working copy)
@@ -163,6 +163,7 @@ cpp_create_reader (enum c_lang lang, has
   CPP_OPTION (pfile, dollars_in_ident) = 1;
   CPP_OPTION (pfile, warn_dollars) = 1;
   CPP_OPTION (pfile, warn_variadic_macros) = 1;
+  CPP_OPTION (pfile, warn_builtin_macro_redefined) = 1;
   CPP_OPTION (pfile, warn_normalize) = normalized_C;
 
   /* Default CPP arithmetic to something sensible for the host for the
@@ -376,7 +377,9 @@ cpp_init_special_builtins (cpp_reader *p
     {
       cpp_hashnode *hp = cpp_lookup (pfile, b->name, b->len);
       hp->type = NT_MACRO;
-      hp->flags |= NODE_BUILTIN | NODE_WARN;
+      hp->flags |= NODE_BUILTIN;
+      if (CPP_OPTION (pfile, warn_builtin_macro_redefined))
+	hp->flags |= NODE_WARN;
       hp->value.builtin = (enum builtin_type) b->value;
     }
 }

^ permalink raw reply	[flat|nested] 16+ messages in thread

end of thread, other threads:[~2008-09-18 15:43 UTC | newest]

Thread overview: 16+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2008-08-22 16:53 [PATCH][RFC] -Wno-... option to suppress builtin macro redefined warnings Simon Baldwin
  -- strict thread matches above, loose matches on Subject: below --
2008-07-30 15:12 Simon Baldwin
2008-07-30 15:27 ` Joseph S. Myers
2008-08-08 16:01 ` Tom Tromey
2008-08-08 16:09   ` Manuel López-Ibáñez
2008-08-08 16:21     ` Tom Tromey
2008-08-08 16:23   ` Simon Baldwin
2008-08-15 17:28     ` Simon Baldwin
     [not found]       ` <48AEE7A7.9000509@google.com>
2008-08-22 17:17         ` Tom Tromey
2008-08-26 18:38           ` Simon Baldwin
2008-09-02 11:29             ` Simon Baldwin
2008-09-13  7:42             ` Tom Tromey
2008-09-16 16:11               ` Simon Baldwin
2008-09-17 14:19               ` Ian Lance Taylor
2008-09-18 16:04                 ` Simon Baldwin
2008-09-17 14:24             ` Ian Lance Taylor

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