[Bug gold/15200] Runtime undefined reference to __exidx_start/_end

[dougkwan at google dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=15200

--- Comment #10 from Doug Kwan <dougkwan at google dot com> 2013-03-13 03:57:35 
UTC ---
I have no object to what is proposed but the decision is Ian's.

On Tue, Mar 12, 2013 at 7:03 PM, petechou at gmail dot com
<address@hidden> wrote:
> http://sourceware.org/bugzilla/show_bug.cgi?id=15200
>
> --- Comment #9 from pete <petechou at gmail dot com> 2013-03-13 02:03:32 UTC 
> ---
> If there is a libfoo.so, it's possible to implement part of functions in
> libfoo.so and then link against libfoo.so again to produce a new library. I
> think the "linker-defined" symbols should also have higher priority than the
> symbols in DSO.
>
> And I also think we should have the same behavior on defining symbol value
> whether only_if_ref is set or not?
>
> The patch will affect 4 ways to define output symbols:
> 1. do_define_in_output_data
> 2. do_define_in_output_segment
> 3. do_define_as_constant
> 4. add_undefined_symbol_from_command_line
>
> For 1, 2, and 3, it makes sense to use the given output section, segment, and
> constant to define symbol values if the "linker-defined" symbols have higher
> priority.
>
> As for 4, I think it doesn't matter.
>
> -
> Thanks,
> Pete
>
> (In reply to comment #8)
>> Hi Pete,
>>
>> 1. My concern of your patch is that it affects all targets, not just
>> ARM.  While it may fix the problem on ARM, I cannot speak for authors
>> of other backends.
>> 2. I am don't have power approve a patch, you need to convince Ian
>> Taylor that this is the right thing to do for all targets.
>> 3. This bug only happens when DSOs incorrectly export __exidx_start &
>> __exidx_end.  These DSOs are considered broken and I strongly
>> recommend you moving to a newer NDK version with DSOs that have proper
>> visibility.  Both ld & gold no longer export these symbols.  The
>> reason for not exporting is explained here in the ld patch:
>>
>> http://sourceware.org/ml/binutils/2009-11/msg00367.html
>>
>> -Doug
>>
>>
>> On Wed, Mar 6, 2013 at 10:43 PM, petechou at gmail dot com
>> <address@hidden> wrote:
>> > http://sourceware.org/bugzilla/show_bug.cgi?id=15200
>> >
>> > --- Comment #7 from pete <petechou at gmail dot com> 2013-03-07 06:43:08 
>> > UTC ---
>> > I can think visibility does matter, but only for exporting the symbol or 
>> > not.
>> > In the previous case, gold does define the __bss symbols but not use the
>> > definition in DSO, so I think we should still define section/segment 
>> > symbols
>> > locally.
>> >
>> > -Pete
>> >
>> > (In reply to comment #6)
>> >> The symbols do not have same visibility.  gold in general is
>> >> compatible with GNU ld.  If you look at src/ld/emulparams/, you will
>> >> set that the __bss symbols are exported but the __exidx symbols are
>> >> defined hidden.  gold matches the behaviour of ld.  If you look at
>> >> defstd.cc in gold, you will again see that some of these symbols are
>> >> hidden but some are not.
>> >>
>> >> -Doug
>> >>
>> >>
>> >> On Wed, Mar 6, 2013 at 9:31 PM, petechou at gmail dot com
>> >> <address@hidden> wrote:
>> >> > http://sourceware.org/bugzilla/show_bug.cgi?id=15200
>> >> >
>> >> > --- Comment #5 from pete <petechou at gmail dot com> 2013-03-07 
>> >> > 05:31:25 UTC ---
>> >> > (In reply to comment #4)
>> >> >> The symbols __exidx_end & __exidx_start were exported incorrectly in
>> >> >> the past.  This is fixed in both ld & gold in the sense that these
>> >> >> symbols are defined by not exported.  I think defining these symbols
>> >> >> when there is a non-weak definition in a DSO is not the right thing to
>> >> >> do.  This is basically multiple definition and usually is an error.
>> >> >
>> >> > If so, all section/segment symbols should be defined (if needed) by not
>> >> > exported?
>> >> >
>> >> > But when there is a non-weak definition in a DSO, it's still possible 
>> >> > to find
>> >> > ld.gold define and export segment symbols like __bss_start (See
>> >> > gold.defstd.cc:214. only_if_ref is set to false). And there is no 
>> >> > multiple
>> >> > definition error.
>> >> >
>> >> > $ readelf -Ds libc.so | grep __bss_start
>> >> >   268 311: 0000d898     0 NOTYPE  GLOBAL DEFAULT ABS __bss_start__
>> >> >   619 470: 0000d898     0 NOTYPE  GLOBAL DEFAULT ABS __bss_start
>> >> >
>> >> > $ arm-linux-androideabi-ld.gold -shared -o libplasma.so plasma.o libc.so
>> >> >
>> >> > $ readelf -s libplasma.so | grep __bss_start
>> >> >     73: 00004148     0 NOTYPE  GLOBAL DEFAULT  ABS __bss_start
>> >> >    168: 00004148     0 NOTYPE  GLOBAL DEFAULT  ABS __bss_start
>> >> >
>> >> >> I am not working on the Android NDK so I can't give you a good
>> >> >> suggestion here.  Does using the latest NDK fixes your problem?
>> >> >>
>> >> >
>> >> > Yes, there is no this issue with the latest NDK.
>> >> >
>> >> > -
>> >> > Thanks,
>> >> > Pete
>> >> >
>> >> > --
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