[Bug c/30457] New: Please warn about va_start(ap, invalid)

[Bug c/30457] New: Please warn about va_start(ap, invalid)

[h dot b dot furuseth at usit dot uio dot no]

Here is some undefined behavior which it would be nice if gcc
warned about, since stdarg is such a hairy part of the standard:

#include <stdarg.h>

void foo(register short paramN, ...)
{
  va_list ap;

  va_start(ap, paramN); // Undefined by C99 7.15.1.4p4 (va_start):
  // "If the parameter parmN is declared with the register storage
  //  class, with a function or array type, or with a type that is
  //  not compatible with the type that results after application of
  //  the default argument promotions, the behavior is undefined."

  // gcc does warn about the following, undefined by C99 7.15.1.1p2:
  (void) va_arg(ap, char);
  // "warning: 'char' is promoted to 'int' when passed through '...'
  //  warning: (so you should pass 'int' not 'char' to 'va_arg')
  //  note: if this code is reached, the program will abort"

  va_end(ap);
}


-- 
           Summary: Please warn about va_start(ap, invalid)
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: h dot b dot furuseth at usit dot uio dot no
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30457

[Bug c/30457] Please warn about va_start(ap, invalid)

[manu at gcc dot gnu dot org]

------- Comment #1 from manu at gcc dot gnu dot org  2007-11-03 15:20 -------
This check could be implemented in builtins.c (fold_builtin_next_arg).


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30457

[Bug c/30457] Please warn about va_start(ap, invalid)

[manu at gcc dot gnu dot org]

------- Comment #2 from manu at gcc dot gnu dot org  2007-11-03 15:32 -------
What about this patch? Does it look correct?

Index: gcc/builtins.c
===================================================================
--- gcc/builtins.c      (revision 129513)
+++ gcc/builtins.c      (working copy)
@@ -11357,6 +11357,29 @@
             it.  */
          warning (0, "second parameter of %<va_start%> not last named
argument");
        }
+
+      /* Undefined by C99 7.15.1.4p4 (va_start):
+         "If the parameter parmN is declared with the register storage
+         class, with a function or array type, or with a type that is
+         not compatible with the type that results after application of
+         the default argument promotions, the behavior is undefined."
+      */
+      if (TREE_CODE (TREE_TYPE (arg)) == FUNCTION_TYPE)
+        {
+          warning (0, "undefined behaviour when second parameter of "
+                   "%<va_start%> is declared of function type");
+        }
+      else if (TREE_CODE (TREE_TYPE (arg)) == ARRAY_TYPE)
+        {
+          warning (0, "undefined behaviour when second parameter of "
+                   "%<va_start%> is declared of array type");
+        }
+      else if (DECL_REGISTER (arg))
+      {
+        warning (0, "undefined behaviour when second parameter of "
+                 "%<va_start%> is declared with %<register%> storage");
+      }
+
       /* We want to verify the second parameter just once before the tree
         optimizers are run and then avoid keeping it in the tree,
         as otherwise we could warn even for correct code like:


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30457

[Bug c/30457] Please warn about va_start(ap, invalid)

[manu at gcc dot gnu dot org]

------- Comment #3 from manu at gcc dot gnu dot org  2008-08-21 19:07 -------
Subject: Bug 30457

Author: manu
Date: Thu Aug 21 19:05:46 2008
New Revision: 139406

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=139406
Log:
2008-08-21  Manuel Lopez-Ibanez  <manu@gcc.gnu.org>

        PR 30457
        * builtins.c (fold_builtin_next_arg): Add warning about undefined
        behaviour.
testsuite/
        * gcc.dg/pr30457.c: New.

Added:
    trunk/gcc/testsuite/gcc.dg/pr30457.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/builtins.c
    trunk/gcc/testsuite/ChangeLog


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30457

[Bug c/30457] Please warn about va_start(ap, invalid)

[manu at gcc dot gnu dot org]

------- Comment #5 from manu at gcc dot gnu dot org  2008-08-21 19:12 -------
Thanks for the report!


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30457

[Bug c/30457] Please warn about va_start(ap, invalid)

[manu at gcc dot gnu dot org]

------- Comment #4 from manu at gcc dot gnu dot org  2008-08-21 19:12 -------
We warn now about "register", the other cases are not warned following the
rationale given here:

http://gcc.gnu.org/ml/gcc-patches/2008-08/msg00819.html

Fixed in GCC 4.4


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30457