AX_C_REFERENCEABLE_PASSED_VA_LIST
Checks whether f(va_list va){ &va; } works as expected.
This macro uses compile-time detection and so is cross-compile ready.
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 https://www.gnu.org/software/autoconf/manual/html_node/Function-Portability.html, http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14557, and http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20951 for further information.
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.
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:
f(va_list va)
{
va_list *vap;
#if HAVE_REFERENCEABLE_PASSED_VA_LIST
vap = &va;
#else
vap = (va_list *)va;
#endif
}
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Copyright © 2008 YAMAMOTO Kengo yamaken@bp.iij4u.or.jp
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