[systemd-bugs] [Bug 79606] New: Accommodate gcc-4.9.0 link-time optimization (LTO) changes

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=79606

          Priority: medium
            Bug ID: 79606
          Assignee: systemd-bugs at lists.freedesktop.org
           Summary: Accommodate gcc-4.9.0 link-time optimization (LTO)
                    changes
        QA Contact: systemd-bugs at lists.freedesktop.org
          Severity: minor
    Classification: Unclassified
                OS: Linux (All)
          Reporter: jpsinthemix at verizon.net
          Hardware: x86 (IA32)
            Status: NEW
           Version: unspecified
         Component: general
           Product: systemd

Hi,

Systemd-213 fails to build (symbols not found/resolved during cgls link step)
under gcc-4.9.0 due to link-time optimization (lto) changes, in particular from
gcc-4.9.0/NEWS:

          + When using a linker plugin, compiling with the -flto option
            now generates slim objects files (.o) which only contain
            intermediate language representation for LTO. Use
            -ffat-lto-objects to create files which contain additionally
            the object code. To generate static libraries suitable for LTO
            processing, use gcc-ar and gcc-ranlib; to list symbols from a
            slim object file use gcc-nm. (Requires that ar, ranlib and nm
            have been compiled with plugin support.)

Both -flto and -ffat-lto-objects are now needed when building and linking
against static libs w/LTO. As a quick fix, I simply added the -ffat-lto-objects
flag to configure

--- systemd-213.old/configure   2014-05-28 02:49:44.026507777 -0400
+++ systemd-213.new/configure   2014-05-31 18:58:26.079036215 -0400
@@ -14970,7 +14970,7 @@ case $CFLAGS in #(
   *-O[12345\ ]*) :

   for flag in \
-               -flto; do
+               -flto -ffat-lto-objects; do

   { $as_echo "$as_me:${as_lineno-$LINENO}: checking if $CC supports flag $flag
in envvar CFLAGS" >&5
 $as_echo_n "checking if $CC supports flag $flag in envvar CFLAGS... " >&6; }
-----------

--- systemd-213.old/configure.ac        2014-05-28 02:49:22.979663817 -0400
+++ systemd-213.new/configure.ac        2014-06-03 16:32:42.752442525 -0400
@@ -180,7 +180,7 @@ CC_CHECK_FLAGS_APPEND([with_cflags], [CF
         --param=ssp-buffer-size=4])
 AS_CASE([$CFLAGS], [*-O[[12345\ ]]*],
         [CC_CHECK_FLAGS_APPEND([with_cflags], [CFLAGS], [\
-               -flto])],
+               -flto -ffat-lto-objects])],
         [AC_MSG_RESULT([skipping -flto, optimization not enabled])])
 AC_SUBST([OUR_CFLAGS], "$with_cflags $sanitizer_cflags")
-----------

thanks much for the great software,
John

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