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Re: Fix, GDL2, EOQualifier (getKey()): args


From: Tim McIntosh
Subject: Re: Fix, GDL2, EOQualifier (getKey()): args
Date: Wed, 23 Apr 2008 09:56:35 -0500

On Apr 23, 2008, at 6:34 AM, David Ayers wrote:
this is addressing changes in EOQualifier getKey(), made on March 30.

2008-03-30  Matt Rice  <address@hidden>

  (getKey): Don't use a pointer to a va_list. See
  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14557

This doesn't work without a pointer to args (I am using Mac OS 10.4 with Intel CPU). It will just stick with the first argument, so obviously the
pointer incremented in the use of va_arg() will not return.
Quote from the discussion on bugzilla:

I don't see anything wrong with using "va_list *". The standard even
says:

   It is permitted to create a pointer to a va_list and pass that
   pointer to another function, in which case the original function
   may make further use of the original list after the other
   function returns.

About passing by value it says:

   The object ap may be passed as an argument to another function;
   if that function invokes the va_arg macro with parameter ap, the
   value of ap in the calling function is indeterminate and shall be
   passed to the va_end macro prior to any further reference to ap

Thanks for the report and the patch! The change was provoked by issues compiling on x86_64. I don't suppose you can test it there? What would
be great is if we could extract the relevant code into a simple test
case for gcc to insure that our approach is portable.

What I gather from the above is:

1. After passing ap to another function by value, it is not valid to use ap in the caller without re-initializing it. Currently _qualifierWithArgs() is violating this rule by passing 'args' in two sequential calls to getKey().

2. It is valid to do this if ap is instead passed by pointer (as in the original code and proposed changes).

3. Taking the address of a va_list that has been passed by value is unportable (see GCC bug comment #14). The original code and the proposed changes do this. It looks like this could be fixed by changing _qualifierWithArgs() to take 'va_list *' instead of 'va_list' and eliminating (or similarly changing the signature of) - qualifierWithQualifierFormat:varargList:.

-Tim





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