[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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