[ld/testsuite] Skip "Mixing PIC and non-PIC" testcase on ARM/AArch64 if when no -fpie or -fPIE

[H.J. Lu]

On Wed, Mar 2, 2016 at 7:38 AM, Jiong Wang <jiong.wang@foss.arm.com> wrote:
>
>>>>>>>>> I'm seeing:
>>>>>>>>>
>>>>>>>>> NA->FAIL: Mixing PIC and non-PIC
>>>>>>>>> on aarch64-none-linux-gnu.
>>>>>>>>
>>>>>>>> You can either fix aarch64 backend or skip the test for aarch64.
>>>>>>>
>>>>>>>
>>>>>>> H.J,
>>>>>>>
>>>>>>>      For your testcase, AArch64 is not generating dynamic relocation
>>>>>>> for
>>>>>>>      weak undefined symbol referenced from non-pic code when linking
>>>>>>>      exectuable, instead, it's resolved to zero during static linking
>>>>>>> stage.
>>>>>>>      As far as I know, this behavior is exactly what's described here
>>>>>>> at
>>>>>>>
>>>>>>>        https://sourceware.org/ml/binutils/2008-04/msg00269.html
>>>>>>>
>>>>>>>      And reading those historical discussions,
>>>>>>>
>>>>>>>       https://sourceware.org/ml/binutils/2008-04/msg00032.html
>>>>>>>       https://sourceware.org/ml/binutils/2008-02/msg00264.html
>>>>>>>
>>>>>>>      Looks to me the ld behavior changes introduced by your patch is
>>>>>>> quite
>>>>>>>      sensitive and there still be lack of consensus.
>>>>>>
>>>>>> What linker change were you referring to?  I only added a testcase.
>>>>>
>>>>>
>>>>> I mean those linker changes added together with this testcase.
>>>>>
>>>>> commit aec6b87e0b66d707ead62ca40d220ee78b4cf5a5
>>>>> Author: H.J. Lu <hjl.tools@gmail.com>
>>>>> Date:   Fri Feb 26 04:16:15 2016 -0800
>>>>>
>>>>>       [x86] Resolve non-PIC undefweak symbols in executable
>>>>>
>>>> As far as aarch64 backend is concerned, I only added a testcase.
>>>
>>>
>>> Well, then why you put it under generic directory? and without
>>> restricting
>>> it
>>> on x86? this is implicitly affect all targets, and enforcing all targets
>>> to
>>> follow
>>> the changes on x86.  I think similar changes should only be encouraged to
>>> other target
>>> if it's conventional rules, or it's clearly documented by generic or that
>>> target's ELF
>>> specification.
>>>
>>> While reading from
>>> http://www.skyfree.org/linux/references/ELF_Format.pdf,
>>>
>>>    "The link editor does not extract archive members to resolve undefined
>>>    weak symbols. Unresolved weak symbols have a zero value."
>>>
>>> Looks to me the spec is even more strict that weak symbol's life is
>>> defined
>>> to be ended
>>> after static linking stage. All unresolved weak symbols are assigned zero
>>> value.
>>>
>>> IMO, the support of weak symbol under various rare and complex scenarios
>>> are
>>> very
>>> target specific, thus I'd either move this testcase under x86 directory
>>> or
>>> put it under
>>> generic directory but enabling it on x86 only initially.  If other
>>> targets
>>> want and start
>>> to support similar features like x86 on weak symbol, then they can be
>>> enabled seperately.
>>> This looks to me is a more clean & acceptable way to other targets.
>>>
>> Have you looked at the testcase I added? Are there anything
>> which are target specific?
>
>
> I do have looked at the testcase, they do be purely C code.
>
> If the convention of generic is syntax generic instead of both syntax and
> sematics, I don't have further comment on this.
>
> Anyway, attached patch skips the non-pie version "Mixing PIC and non-PIC"
> testcase.
>
> Not sure if it's trivial enough to qualify obvious, so OK for master branch?
>
> 2016-03-02  Jiong Wang  <jiong.wang@arm.com>
>
> ld/testsuite/
>
>   * ld-elf/shared.exp (mix_pic_and_non_pic): Only run on ARM and AArch64
>     when -fPIE or -fpie specified.

That is wrong.  If you don't want to see FAIL, you can skip the whole.
mix_pic_and_non_pic.  Please don't modify mix_pic_and_non_pic.

-- 
H.J.