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Re: LTO and version scripts


On Tue, Aug 05, 2014 at 08:18:06PM -0400, Ulrich Drepper wrote:
> On Tue, Aug 5, 2014 at 12:57 AM, Alan Modra <amodra@gmail.com> wrote:
> > What version linker?  In particular, do you have the fix for PR12975?
> 
> The Fedora 19 version.  I think it hasn't changed since then which
> means it is 2.23.88.0.1-13 (from the RPM version number).  No idea
> whether that fix is included and unfortunately won't have time to try
> before the weekend.

Both Fedora 19 and 20 have the patch needed for this to work.  Hmm, I
suppose the other thing necessary is a gcc that implements
LDPT_GET_SYMBOLS_V2.  You may be lacking that.  Here's what I see with
mainline gcc and ld.

cat > ltoshare.c <<\EOF
int
cond (void)
{
  return 0;
}

extern void something (void);

int
main (void)
{
  if (cond ())
    something ();
  return 0;
}
EOF
cat > ltoshare.ver <<\EOF
{
  global: main;
  local: *;
};
EOF
~/build/gcc-current/gcc/xgcc -B ~/build/gcc-current/gcc/ -B ld/tmpdir/ld -O2 -fPIC -flto -c ltoshare.c
~/build/gcc-current/gcc/xgcc -B ~/build/gcc-current/gcc/ -B ld/tmpdir/ld -shared -flto -o ltoshare.so ltoshare.o
nm -D ltoshare.so | grep something
                 U something
~/build/gcc-current/gcc/xgcc -B ~/build/gcc-current/gcc/ -B ld/tmpdir/ld -shared -flto -o ltoshare.so ltoshare.o -Wl,--version-script=ltoshare.ver
nm -D ltoshare.so | grep something


-- 
Alan Modra
Australia Development Lab, IBM


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