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Date: Thu, 4 Feb 2010 12:10:27 +0000
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] "Enable _FORTIFY_SOURCE=2" result in building
	failure for qemu-img.c
Message-ID: <20100204121027.GA10297@shareable.org>
References: <201002041504.52626.sheng@linux.intel.com>
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To: Sheng Yang <sheng@linux.intel.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>, Anthony Liguori <aliguori@us.ibm.com>, qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>

Sheng Yang wrote:
>     printf("qemu-img version " QEMU_VERSION ", Copyright (c) 2004-2008 Fabrice 
> Bellard\n"
>            "usage: qemu-img command [command options]\n"
>            "QEMU disk image utility\n"
>            "\n"
>            "Command syntax:\n"
> #define DEF(option, callback, arg_string)        \
>            "  " arg_string "\n"
> #include "qemu-img-cmds.h"
> #undef DEF
> #undef GEN_DOCS
> ....
> 
> Seems gcc take "printf" as a marco. I added a "#undef printf" before the line, 
> then it works...
> 
> So any clue on what's happened and how to fix?

You can't have preprocessor directives inside the arguments of a macro
call.  Yes it's occasionally annoying like this.

You can prevent the macro call without #undef by writing:

    (printf)("qemu-img version " ...etc)

I'm not sure if Glibc is compliant with ISO C by
making printf into a macro that takes arguments.

Certain functions such as putchar() are specified as being allowed to
be macros, which implies the other standard functions aren't.

-- Jamie