--- /dev/null
+# ===========================================================================
+# https://www.gnu.org/software/autoconf-archive/ax_sys_weak_alias.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+# AX_SYS_WEAK_ALIAS
+#
+# DESCRIPTION
+#
+# Determines whether weak aliases are supported on the system, and if so,
+# what scheme is used to declare them. Also checks to see if aliases can
+# cross object file boundaries, as some systems don't permit them to.
+#
+# Most systems permit something called a "weak alias" or "weak symbol."
+# These aliases permit a library to provide a stub form of a routine
+# defined in another library, thus allowing the first library to operate
+# even if the other library is not linked. This macro will check for
+# support of weak aliases, figure out what schemes are available, and
+# determine some characteristics of the weak alias support -- primarily,
+# whether a weak alias declared in one object file may be referenced from
+# another object file.
+#
+# There are four known schemes of declaring weak symbols; each scheme is
+# checked in turn, and the first one found is preferred. Note that only
+# one of the mentioned preprocessor macros will be defined!
+#
+# 1. Function attributes
+#
+# This scheme was first introduced by the GNU C compiler, and attaches
+# attributes to particular functions. It is among the easiest to use, and
+# so is the first one checked. If this scheme is detected, the
+# preprocessor macro HAVE_SYS_WEAK_ALIAS_ATTRIBUTE will be defined to 1.
+# This scheme is used as in the following code fragment:
+#
+# void __weakf(int c)
+# {
+# /* Function definition... */
+# }
+#
+# void weakf(int c) __attribute__((weak, alias("__weakf")));
+#
+# 2. #pragma weak
+#
+# This scheme is in use by many compilers other than the GNU C compiler.
+# It is also particularly easy to use, and fairly portable -- well, as
+# portable as these things get. If this scheme is detected first, the
+# preprocessor macro HAVE_SYS_WEAK_ALIAS_PRAGMA will be defined to 1. This
+# scheme is used as in the following code fragment:
+#
+# extern void weakf(int c);
+# #pragma weak weakf = __weakf
+# void __weakf(int c)
+# {
+# /* Function definition... */
+# }
+#
+# 3. #pragma _HP_SECONDARY_DEF
+#
+# This scheme appears to be in use by the HP compiler. As it is rather
+# specialized, this is one of the last schemes checked. If it is the first
+# one detected, the preprocessor macro HAVE_SYS_WEAK_ALIAS_HPSECONDARY
+# will be defined to 1. This scheme is used as in the following code
+# fragment:
+#
+# extern void weakf(int c);
+# #pragma _HP_SECONDARY_DEF __weakf weakf
+# void __weakf(int c)
+# {
+# /* Function definition... */
+# }
+#
+# 4. #pragma _CRI duplicate
+#
+# This scheme appears to be in use by the Cray compiler. As it is rather
+# specialized, it too is one of the last schemes checked. If it is the
+# first one detected, the preprocessor macro
+# HAVE_SYS_WEAK_ALIAS_CRIDUPLICATE will be defined to 1. This scheme is
+# used as in the following code fragment:
+#
+# extern void weakf(int c);
+# #pragma _CRI duplicate weakf as __weakf
+# void __weakf(int c)
+# {
+# /* Function definition... */
+# }
+#
+# In addition to the preprocessor macros listed above, if any scheme is
+# found, the preprocessor macro HAVE_SYS_WEAK_ALIAS will also be defined
+# to 1.
+#
+# Once a weak aliasing scheme has been found, a check will be performed to
+# see if weak aliases are honored across object file boundaries. If they
+# are, the HAVE_SYS_WEAK_ALIAS_CROSSFILE preprocessor macro is defined to
+# 1.
+#
+# This Autoconf macro also makes two substitutions. The first, WEAK_ALIAS,
+# contains the name of the scheme found (one of "attribute", "pragma",
+# "hpsecondary", or "criduplicate"), or "no" if no weak aliasing scheme
+# was found. The second, WEAK_ALIAS_CROSSFILE, is set to "yes" or "no"
+# depending on whether or not weak aliases may cross object file
+# boundaries.
+#
+# LICENSE
+#
+# Copyright (c) 2008 Kevin L. Mitchell <klmitch@mit.edu>
+#
+# 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. This file is offered as-is, without any
+# warranty.
+
+#serial 8
+
+AU_ALIAS([KLM_SYS_WEAK_ALIAS], [AX_SYS_WEAK_ALIAS])
+AC_DEFUN([AX_SYS_WEAK_ALIAS], [
+ # starting point: no aliasing scheme yet...
+ ax_sys_weak_alias=no
+
+ # Figure out what kind of aliasing may be supported...
+ _AX_SYS_WEAK_ALIAS_ATTRIBUTE
+ _AX_SYS_WEAK_ALIAS_PRAGMA
+ _AX_SYS_WEAK_ALIAS_HPSECONDARY
+ _AX_SYS_WEAK_ALIAS_CRIDUPLICATE
+
+ # Do we actually support aliasing?
+ AC_CACHE_CHECK([how to create weak aliases with $CC],
+ [ax_cv_sys_weak_alias],
+ [ax_cv_sys_weak_alias=$ax_sys_weak_alias])
+
+ # OK, set a #define
+ AS_IF([test $ax_cv_sys_weak_alias != no], [
+ AC_DEFINE([HAVE_SYS_WEAK_ALIAS], 1,
+ [Define this if your system can create weak aliases])
+ ])
+
+ # Can aliases cross object file boundaries?
+ _AX_SYS_WEAK_ALIAS_CROSSFILE
+
+ # OK, remember the results
+ AC_SUBST([WEAK_ALIAS], [$ax_cv_sys_weak_alias])
+ AC_SUBST([WEAK_ALIAS_CROSSFILE], [$ax_cv_sys_weak_alias_crossfile])
+])
+
+AC_DEFUN([_AX_SYS_WEAK_ALIAS_ATTRIBUTE],
+[ # Test whether compiler accepts __attribute__ form of weak aliasing
+ AC_CACHE_CHECK([whether $CC accepts function __attribute__((weak,alias()))],
+ [ax_cv_sys_weak_alias_attribute], [
+ # We add -Werror if it's gcc to force an error exit if the weak attribute
+ # isn't understood
+ AS_IF([test $GCC = yes], [
+ save_CFLAGS=$CFLAGS
+ CFLAGS=-Werror])
+
+ # Try linking with a weak alias...
+ AC_LINK_IFELSE([
+ AC_LANG_PROGRAM([
+void __weakf(int c) {}
+void weakf(int c) __attribute__((weak, alias("__weakf")));],
+ [weakf(0)])],
+ [ax_cv_sys_weak_alias_attribute=yes],
+ [ax_cv_sys_weak_alias_attribute=no])
+
+ # Restore original CFLAGS
+ AS_IF([test $GCC = yes], [
+ CFLAGS=$save_CFLAGS])
+ ])
+
+ # What was the result of the test?
+ AS_IF([test $ax_sys_weak_alias = no &&
+ test $ax_cv_sys_weak_alias_attribute = yes], [
+ ax_sys_weak_alias=attribute
+ AC_DEFINE([HAVE_SYS_WEAK_ALIAS_ATTRIBUTE], 1,
+ [Define this if weak aliases may be created with __attribute__])
+ ])
+])
+
+AC_DEFUN([_AX_SYS_WEAK_ALIAS_PRAGMA],
+[ # Test whether compiler accepts #pragma form of weak aliasing
+ AC_CACHE_CHECK([whether $CC supports @%:@pragma weak],
+ [ax_cv_sys_weak_alias_pragma], [
+
+ # Try linking with a weak alias...
+ AC_LINK_IFELSE([
+ AC_LANG_PROGRAM([
+extern void weakf(int c);
+@%:@pragma weak weakf = __weakf
+void __weakf(int c) {}],
+ [weakf(0)])],
+ [ax_cv_sys_weak_alias_pragma=yes],
+ [ax_cv_sys_weak_alias_pragma=no])
+ ])
+
+ # What was the result of the test?
+ AS_IF([test $ax_sys_weak_alias = no &&
+ test $ax_cv_sys_weak_alias_pragma = yes], [
+ ax_sys_weak_alias=pragma
+ AC_DEFINE([HAVE_SYS_WEAK_ALIAS_PRAGMA], 1,
+ [Define this if weak aliases may be created with @%:@pragma weak])
+ ])
+])
+
+AC_DEFUN([_AX_SYS_WEAK_ALIAS_HPSECONDARY],
+[ # Test whether compiler accepts _HP_SECONDARY_DEF pragma from HP...
+ AC_CACHE_CHECK([whether $CC supports @%:@pragma _HP_SECONDARY_DEF],
+ [ax_cv_sys_weak_alias_hpsecondary], [
+
+ # Try linking with a weak alias...
+ AC_LINK_IFELSE([
+ AC_LANG_PROGRAM([
+extern void weakf(int c);
+@%:@pragma _HP_SECONDARY_DEF __weakf weakf
+void __weakf(int c) {}],
+ [weakf(0)])],
+ [ax_cv_sys_weak_alias_hpsecondary=yes],
+ [ax_cv_sys_weak_alias_hpsecondary=no])
+ ])
+
+ # What was the result of the test?
+ AS_IF([test $ax_sys_weak_alias = no &&
+ test $ax_cv_sys_weak_alias_hpsecondary = yes], [
+ ax_sys_weak_alias=hpsecondary
+ AC_DEFINE([HAVE_SYS_WEAK_ALIAS_HPSECONDARY], 1,
+ [Define this if weak aliases may be created with @%:@pragma _HP_SECONDARY_DEF])
+ ])
+])
+
+AC_DEFUN([_AX_SYS_WEAK_ALIAS_CRIDUPLICATE],
+[ # Test whether compiler accepts "_CRI duplicate" pragma from Cray
+ AC_CACHE_CHECK([whether $CC supports @%:@pragma _CRI duplicate],
+ [ax_cv_sys_weak_alias_criduplicate], [
+
+ # Try linking with a weak alias...
+ AC_LINK_IFELSE([
+ AC_LANG_PROGRAM([
+extern void weakf(int c);
+@%:@pragma _CRI duplicate weakf as __weakf
+void __weakf(int c) {}],
+ [weakf(0)])],
+ [ax_cv_sys_weak_alias_criduplicate=yes],
+ [ax_cv_sys_weak_alias_criduplicate=no])
+ ])
+
+ # What was the result of the test?
+ AS_IF([test $ax_sys_weak_alias = no &&
+ test $ax_cv_sys_weak_alias_criduplicate = yes], [
+ ax_sys_weak_alias=criduplicate
+ AC_DEFINE([HAVE_SYS_WEAK_ALIAS_CRIDUPLICATE], 1,
+ [Define this if weak aliases may be created with @%:@pragma _CRI duplicate])
+ ])
+])
+
+dnl Note: This macro is modeled closely on AC_LINK_IFELSE, and in fact
+dnl depends on some implementation details of that macro, particularly
+dnl its use of _AC_MSG_LOG_CONFTEST to log the failed test program and
+dnl its use of ac_link for running the linker.
+AC_DEFUN([_AX_SYS_WEAK_ALIAS_CROSSFILE],
+[ # Check to see if weak aliases can cross object file boundaries
+ AC_CACHE_CHECK([whether $CC supports weak aliases across object file boundaries],
+ [ax_cv_sys_weak_alias_crossfile], [
+ AS_IF([test $ax_cv_sys_weak_alias = no],
+ [ax_cv_sys_weak_alias_crossfile=no], [
+dnl Must build our own test files...
+ # conftest1 contains our weak alias definition...
+ cat >conftest1.$ac_ext <<_ACEOF
+/* confdefs.h. */
+_ACEOF
+ cat confdefs.h >>conftest1.$ac_ext
+ cat >>conftest1.$ac_ext <<_ACEOF
+/* end confdefs.h. */
+
+@%:@ifndef HAVE_SYS_WEAK_ALIAS_ATTRIBUTE
+extern void weakf(int c);
+@%:@endif
+@%:@if defined(HAVE_SYS_WEAK_ALIAS_PRAGMA)
+@%:@pragma weak weakf = __weakf
+@%:@elif defined(HAVE_SYS_WEAK_ALIAS_HPSECONDARY)
+@%:@pragma _HP_SECONDARY_DEF __weakf weakf
+@%:@elif defined(HAVE_SYS_WEAK_ALIAS_CRIDUPLICATE)
+@%:@pragma _CRI duplicate weakf as __weakf
+@%:@endif
+void __weakf(int c) {}
+@%:@ifdef HAVE_SYS_WEAK_ALIAS_ATTRIBUTE
+void weakf(int c) __attribute((weak, alias("__weakf")));
+@%:@endif
+_ACEOF
+ # And conftest2 contains our main routine that calls it
+ cat >conftest2.$ac_ext <<_ACEOF
+/* confdefs.h. */
+_ACEOF
+ cat confdefs.h >> conftest2.$ac_ext
+ cat >>conftest2.$ac_ext <<_ACEOF
+/* end confdefs.h. */
+
+extern void weakf(int c);
+int
+main ()
+{
+ weakf(0);
+ return 0;
+}
+_ACEOF
+ # We must remove the object files (if any) ourselves...
+ rm -f conftest2.$ac_objext conftest$ac_exeext
+
+ # Change ac_link to compile *2* files together
+ save_aclink=$ac_link
+ ac_link=`echo "$ac_link" | \
+ sed -e 's/conftest\(\.\$ac_ext\)/conftest1\1 conftest2\1/'`
+dnl Substitute our own routine for logging the conftest
+m4_pushdef([_AC_MSG_LOG_CONFTEST],
+[echo "$as_me: failed program was:" >&AS_MESSAGE_LOG_FD
+echo ">>> conftest1.$ac_ext" >&AS_MESSAGE_LOG_FD
+sed "s/^/| /" conftest1.$ac_ext >&AS_MESSAGE_LOG_FD
+echo ">>> conftest2.$ac_ext" >&AS_MESSAGE_LOG_FD
+sed "s/^/| /" conftest2.$ac_ext >&AS_MESSAGE_LOG_FD
+])dnl
+ # Since we created the files ourselves, don't use SOURCE argument
+ AC_LINK_IFELSE(, [ax_cv_sys_weak_alias_crossfile=yes],
+ [ax_cv_sys_weak_alias_crossfile=no])
+dnl Restore _AC_MSG_LOG_CONFTEST
+m4_popdef([_AC_MSG_LOG_CONFTEST])dnl
+ # Restore ac_link
+ ac_link=$save_aclink
+
+ # We must remove the object files (if any) and C files ourselves...
+ rm -f conftest1.$ac_ext conftest2.$ac_ext \
+ conftest1.$ac_objext conftest2.$ac_objext
+ ])
+ ])
+
+ # What were the results of the test?
+ AS_IF([test $ax_cv_sys_weak_alias_crossfile = yes], [
+ AC_DEFINE([HAVE_SYS_WEAK_ALIAS_CROSSFILE], 1,
+ [Define this if weak aliases in other files are honored])
+ ])
+])
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