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From: "carlos at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug build/15658] New: Support building glibc with -flto.
Date: Thu, 20 Jun 2013 12:57:00 -0000
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X-Bugzilla-Product: glibc
X-Bugzilla-Component: build
X-Bugzilla-Version: 2.18
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X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: carlos at redhat dot com
X-Bugzilla-Status: NEW
X-Bugzilla-Priority: P2
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http://sourceware.org/bugzilla/show_bug.cgi?id=15658

            Bug ID: 15658
           Summary: Support building glibc with -flto.
           Product: glibc
           Version: 2.18
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: build
          Assignee: unassigned at sourceware dot org
          Reporter: carlos at redhat dot com
                CC: carlos at redhat dot com

You can't build glibc with -flto.

glibc master is currently unbuildable with -flto because of:
http://sourceware.org/bugzilla/show_bug.cgi?id=15648

You should always see:
checking for .preinit_array/.init_array/.fini_array support... no
configure: error: Need linker with .init_array/.fini_array support.

This is because -flto throws out the .init_array support.

A potential fix is:
diff --git a/configure.in b/configure.in
index 8b11081..415e777 100644
--- a/configure.in
+++ b/configure.in
@@ -1383,7 +1383,7 @@ AC_CACHE_CHECK(for .preinit_array/.init_array/.fini_array
support,
               libc_cv_initfini_array, [dnl
 LIBC_TRY_LINK_STATIC([
 int foo (void) { return 1; }
-int (*fp) (void) __attribute__ ((section (".init_array"))) = foo;
+int (*fp) (void) __attribute__ ((section (".init_array"), used)) = foo;
 ],
   [if $READELF -S conftest | fgrep INIT_ARRAY > /dev/null; then
     libc_cv_initfini_array=yes
~~~

However, given that nobody has built with -flto it's going to require
considerable work to make it happen.

This is an enhancement.

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