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##### http://autoconf-archive.cryp.to/ax_c_referenceable_passed_va_list.html
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# AX_C_REFERENCEABLE_PASSED_VA_LIST
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# Checks whether f(va_list va){ &va; } works as expected.
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# This macro uses compile-time detection and so is cross-compile
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# C99 mentioned passing a pointer to va_list to other functions
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# (footnote 212 of "7.15 Variable arguments <stdarg.h>"). However,
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# f(va_list va) { &va; } produces broken pointer on some environments
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# such as gcc on x86_64, although { va_list va; &va; } works as
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# expected. See the detection code of this file and any of pages
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# http://www.gnu.org/software/autoconf/manual/html_node/Function-Portability.html,
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# http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14557, and
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# http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20951 for further
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# Although C99 does not define the operations f(va_list va) { &va; }
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# and &va itself as standard (footnotes are declared as "normative
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# part, information only"), certain situations need it. This macro
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# provides a type detection about va_list implementation to deal with
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# Following workaround will probably work on such environments
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# although it does not ensure to be safe and portable. At least it is
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# working on x86_64-unknown-linux-gnu:
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# #if HAVE_REFERENCEABLE_PASSED_VA_LIST
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# vap = (va_list *)va;
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# Copyright (c) 2006 YAMAMOTO Kengo <yamaken AT bp.iij4u.or.jp>
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# Copying and distribution of this file, with or without
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# modification, are permitted in any medium without royalty provided
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# the copyright notice and this notice are preserved.
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AC_DEFUN([AX_C_REFERENCEABLE_PASSED_VA_LIST], [
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AC_CACHE_CHECK([whether f(va_list va){ &va; } works as expected],
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[ax_cv_c_referenceable_passed_va_list],
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volatile va_list g_va;
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/* typeof(callee_va) differs from typeof(caller_va) by a compiler trick, if
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* va_list is implemented as an array. On such environment, this copy
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va_start(caller_va, last);
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vf(caller_va); /* passed as &caller_va[0] if va_list is an array type */
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main(int argc, char *argv[])
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f(0xdeadbeef, 0xfedbeef, 0xfeedee);
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[ax_cv_c_referenceable_passed_va_list=yes],
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[ax_cv_c_referenceable_passed_va_list=no])])
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if test "x$ax_cv_c_referenceable_passed_va_list" = xyes; then
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AC_DEFINE([HAVE_REFERENCEABLE_PASSED_VA_LIST], [1],
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[Define to 1 if f(va_list va){ &va; } works as expected.])
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sigscheme/m4/ax_c_referenceable_passed_va_list.m4
