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Autoconf Macro: ax_c_referenceable_passed_va_list
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<h1>
ax_c_referenceable_passed_va_list
</h1>
<h2>
SYNOPSIS
</h2>
<p class="indent" style="white-space:nowrap;">
<code>AX_C_REFERENCEABLE_PASSED_VA_LIST</code>
</p>
<h2>
DESCRIPTION
</h2>
<div class="indent">
<p>
Checks whether f(va_list va){ &va; } works as expected.
</p>
<p>
This macro uses compile-time detection and so is cross-compile ready.
</p>
<p>
C99 mentioned passing a pointer to va_list to other functions (footnote 212
of "7.15 Variable arguments <stdarg.h>"). However, f(va_list va) {
&va; } produces broken pointer on some environments such as gcc on
x86_64, although { va_list va; &va; } works as expected. See the
detection code of this file and any of pages <a href=
"http://www.gnu.org/software/autoconf/manual/html_node/Function-Portability.html">
http://www.gnu.org/software/autoconf/manual/html_node/Function-Portability.html</a>,
<a href=
"http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14557">http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14557</a>,
and <a href=
"http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20951">http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20951</a>
for further information.
</p>
<p>
Although C99 does not define the operations f(va_list va) { &va; } and
&va itself as standard (footnotes are declared as "normative part,
information only"), certain situations need it. This macro provides a type
detection about va_list implementation to deal with the operation.
</p>
<p>
Following workaround will probably work on such environments although it
does not ensure to be safe and portable. At least it is working on
x86_64-unknown-linux-gnu:
</p>
<pre>
f(va_list va)
{
va_list *vap;
#if HAVE_REFERENCEABLE_PASSED_VA_LIST
vap = &va;
#else
vap = (va_list *)va;
#endif
}
</pre>
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<h2>
SOURCE CODE
</h2>
<p class="indent">
<a href=
"http://autoconf-archive.cryp.to/ax_c_referenceable_passed_va_list.m4">http://autoconf-archive.cryp.to/ax_c_referenceable_passed_va_list.m4</a>
</p>
<h2>
LICENSE
</h2>
<div class="indent">
<p style="white-space:nowrap;">
Copyright © 2008 YAMAMOTO Kengo <yamaken AT bp.iij4u.or.jp>
</p>
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Copying and distribution of this file, with or without modification, are
permitted in any medium without royalty provided the copyright notice and
this notice are preserved.
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