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Diffstat (limited to 'm4')
| -rw-r--r-- | m4/ax_sys_weak_alias.m4 | 337 |
1 files changed, 337 insertions, 0 deletions
diff --git a/m4/ax_sys_weak_alias.m4 b/m4/ax_sys_weak_alias.m4 new file mode 100644 index 00000000..7c632a0e --- /dev/null +++ b/m4/ax_sys_weak_alias.m4 @@ -0,0 +1,337 @@ +# =========================================================================== +# http://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 prefered. 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 6 + +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]) + ]) +]) |