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Re: [PATCH] PR ld/19579: [Regression] link error linking fortran code with PIE


On Mon, Mar 7, 2016 at 7:28 AM, Alan Modra <amodra@gmail.com> wrote:
> On Fri, Mar 04, 2016 at 07:41:42PM -0800, H.J. Lu wrote:
>> On Fri, Mar 4, 2016 at 5:52 PM, Alan Modra <amodra@gmail.com> wrote:
>> > On Fri, Mar 04, 2016 at 05:48:33AM -0800, H.J. Lu wrote:
>> >> --- a/bfd/elflink.c
>> >> +++ b/bfd/elflink.c
>> >> @@ -1172,9 +1172,12 @@ _bfd_elf_merge_symbol (bfd *abfd,
>> >>
>> >>    newdef = !bfd_is_und_section (sec) && !bfd_is_com_section (sec);
>> >>
>> >> +  /* The old common symbol in executable is a definition if the new
>> >> +     definition comes from a shared library.  */
>> >>    olddef = (h->root.type != bfd_link_hash_undefined
>> >>           && h->root.type != bfd_link_hash_undefweak
>> >> -         && h->root.type != bfd_link_hash_common);
>> >> +         && (h->root.type != bfd_link_hash_common
>> >> +             || (!olddyn && newdyn && bfd_link_executable (info))));
>> >>
>> >>    /* NEWFUNC and OLDFUNC indicate whether the new or old symbol,
>> >>       respectively, appear to be a function.  */
>> >
>> > Why is this the correct place to change, and not code after the
>> > comment "We treat a common symbol as a definition"?
>>
>> olddef has been checked well before that.
>
> And do any of those matter?

[hjl@gnu-6 pr19579b]$ cat foo.c
__thread int foo[2];
[hjl@gnu-6 pr19579b]$ cat x.c
#include <stdio.h>

int foo[1];

int
main ()
{
  if (foo[0] == 0)
    printf ("PASS\n");
  return 0;
}
[hjl@gnu-6 pr19579b]$ make
gcc  -pie -B./ -fPIE -O0   -c -o x.o x.c
gcc  -pie -B./ -fPIE -O0 -fPIC   -c -o foo.o foo.c
gcc  -pie -B./ -shared -o libfoo.so foo.o
gcc  -pie -B./ -o x x.o libfoo.so -Wl,-R.
./ld: foo: TLS definition in libfoo.so section .tbss mismatches
non-TLS reference in x.o
libfoo.so: error adding symbols: Bad value
collect2: error: ld returned 1 exit status
Makefile:17: recipe for target 'x' failed
make: *** [x] Error 1

vs

[hjl@gnu-6 pr19579b]$ gcc  -pie  -o x x.o libfoo.so -Wl,-R.
/usr/local/bin/ld: foo: TLS definition in libfoo.so section .tbss
mismatches non-TLS definition in x.o section COMMON
libfoo.so: error adding symbols: Bad value
collect2: error: ld returned 1 exit status
[hjl@gnu-6 pr19579b]$

>> We need to get it right.
>
> That's why I asked.  You haven't yet replied with anything more than a
> superficial reason for not moving the change to where it ought to go,
> I think.

The old common symbol is a definition in this case.  Why shouldn't
olddef set to yes?


-- 
H.J.


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