[lttng-dev] [PATCH lttng-ust] Add a configure check for weak symbols support
Jérémie Galarneau
jeremie.galarneau at efficios.com
Mon Nov 17 13:20:01 EST 2014
On Mon, Nov 17, 2014 at 1:16 PM, Mathieu Desnoyers
<mathieu.desnoyers at efficios.com> wrote:
> Merged into master, stable-2.6, stable-2.5, stable-2.4.
>
> A big thanks to jgalar for reminding me to email
> this reply.
That's what you get for bugging me about my "merged" e-mails! ;)
Jérémie
>
> :-P
>
> Mathieu
>
> ----- Original Message -----
>> From: "Christian Babeux" <christian.babeux at efficios.com>
>> To: lttng-dev at lists.lttng.org
>> Cc: "mathieu desnoyers" <mathieu.desnoyers at efficios.com>, "Christian Babeux" <christian.babeux at efficios.com>
>> Sent: Wednesday, November 12, 2014 8:35:21 PM
>> Subject: [PATCH lttng-ust] Add a configure check for weak symbols support
>>
>> Fixes #236
>>
>> Signed-off-by: Christian Babeux <christian.babeux at efficios.com>
>> ---
>> config/ax_sys_weak_alias.m4 | 337
>> ++++++++++++++++++++++++++++++++++++++++++++
>> configure.ac | 7 +
>> 2 files changed, 344 insertions(+)
>> create mode 100644 config/ax_sys_weak_alias.m4
>>
>> diff --git a/config/ax_sys_weak_alias.m4 b/config/ax_sys_weak_alias.m4
>> new file mode 100644
>> index 0000000..e1bfd33
>> --- /dev/null
>> +++ b/config/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 at 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 $ax_cv_sys_weak_alias_crossfile = yes], [
>> + AC_DEFINE([HAVE_SYS_WEAK_ALIAS_CROSSFILE], 1,
>> + [Define this if weak aliases in other files are honored])
>> + ])
>> +])
>> diff --git a/configure.ac b/configure.ac
>> index 18f3739..f84f426 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -106,6 +106,13 @@ AC_CACHE_CHECK([whether the C++ compiler works],
>>
>> AM_CONDITIONAL([CXX_WORKS], [test "x$rw_cv_prog_cxx_works" = "xyes"])
>>
>> +# Check if the compiler support weak symbols
>> +AX_SYS_WEAK_ALIAS
>> +
>> +if test "x${ax_cv_sys_weak_alias}" = "xno"; then
>> + AC_MSG_ERROR([Your platform doesn't support weak symbols.])
>> +fi
>> +
>> ## Checks for libraries.
>> AC_CHECK_LIB([dl], [dlopen],
>> [
>> --
>> 2.1.1
>>
>>
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
>
> _______________________________________________
> lttng-dev mailing list
> lttng-dev at lists.lttng.org
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
--
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com
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