[PATCH] Skip convert lui to GPREL_L for .LANCHOR

[Lifang Xia]

Hi Nelson,

Thank you for your notice.
C-SKY has signed the copyrights. lifang_xia@c-sky.com is my email for 
C-SKY. Could you replace my email with lifang_xia@c-sky.com?
And I will check that whether Alibaba signed the copyright for binutils 
and gdb or not.

Thanks,
Lifang


在 2021/3/19 16:31, Nelson Chu 写道:
> Hi Jim and MaskRay,
>
> Thanks for your feedback and clarification.  The lld's behavior looks
> interesting, I will find some time to see the details if possible.
>
> Hi Lifang,
>
> Thanks for your reporting.  I may have time and can come back to see
> this problem next week.  I prefer to keep your name in the ChangeLog
> and as the co-author in my following fixes, to credit your
> contribution.  But unfortunately we notice that Alibaba only have the
> copyright assignments for gcc and glibc, you might don't have the ones
> for binutils and gdb, so we cannot commit your patches or keep your
> name/company.  Do you have any plan to sign the copyrights for
> binutils and gdb?  It's should be helpful and convenience if you are
> willing to doing contributions for binutils and gdb in the future.
> The process may need some times, so it would be great if you can start
> to run the it recently.
>
> Thanks
> Nelson
>
> On Tue, Mar 16, 2021 at 2:49 PM Fāng-ruì Sòng <maskray@google.com> wrote:
>> On Fri, Mar 12, 2021 at 5:51 AM Nelson Chu <nelson.chu@sifive.com> wrote:
>>> Thanks!
>>>
>>> I have given my thoughts on the bugzilla, but I think it would be good
>>> to get more suggestions from other maintainers, including the experts
>>> from llvm and lld.
>>> What do you think?  Please feel free to share your thoughts if you are
>>> interested and have times :)
>>>
>>> Thank you very much
>>> Nelson
>>>
>>> On Fri, Mar 12, 2021 at 11:22 AM Lifang Xia
>>> <lifang_xia@linux.alibaba.com> wrote:
>>>> Hi Nelson,
>>>>
>>>> I report a bug here: https://sourceware.org/bugzilla/show_bug.cgi?id=27566
>>>>
>>>> BRs,
>>>> Lifang
>>>>
>>>> 在 2021/3/12 10:38, Nelson Chu 写道:
>>>>> Hi Lifang,
>>>>>
>>>>> Could you add the ld testcase for this?  It's better to report the
>>>>> details somewhere, like sourceware bugzilla or riscv github.  I find a
>>>>> similar fix in PR25258,
>>>>> https://sourceware.org/bugzilla/show_bug.cgi?id=25258.  The patch
>>>>> works only for c.lui relaxation, so I think we might need a similar
>>>>> fix for the regular lui to gp relaxation, rather than just disable the
>>>>> relaxation.  Anyway, we need a testcase or at least a reduced case can
>>>>> be reproduced.
>>>>>
>>>>> Thanks
>>>>> Nelson
>>>>>
>>>>> On Thu, Mar 11, 2021 at 9:05 PM Lifang Xia via Binutils
>>>>> <binutils@sourceware.org> wrote:
>>>>>> If the .LANCHOR defined in .rodata, the gp may not reach the symbol
>>>>>> after lang_size_relro_segment while linking with "-z relro".
>>>>>>
>>>>>> bfd/
>>>>>>           * elfnn-riscv.c (_bfd_riscv_relax_lui): Skip that the symbol
>>>>>>             is defined in rodata and linking with "-z relro".
>>>>>> ---
>>>>>>    bfd/elfnn-riscv.c | 12 ++++++++----
>>>>>>    1 file changed, 8 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
>>>>>> index 364d67b..74dce3c 100644
>>>>>> --- a/bfd/elfnn-riscv.c
>>>>>> +++ b/bfd/elfnn-riscv.c
>>>>>> @@ -4251,10 +4251,14 @@ _bfd_riscv_relax_lui (bfd *abfd,
>>>>>>         Valid gp range conservatively because of alignment issue.  */
>>>>>>      if (undefined_weak
>>>>>>          || (VALID_ITYPE_IMM (symval)
>>>>>> -         || (symval >= gp
>>>>>> -             && VALID_ITYPE_IMM (symval - gp + max_alignment + reserve_size))
>>>>>> -         || (symval < gp
>>>>>> -             && VALID_ITYPE_IMM (symval - gp - max_alignment - reserve_size))))
>>>>>> +         /* Skip that the symbol defined in rodata by .set, such as .LANCHOR,
>>>>>> +            and link with -z relro. The symbol may not be accessed with gp.  */
>>>>>> +         || (!(sym_sec->flags & SEC_READONLY
>>>>>> +               && link_info->relro)
>>>>>> +             && ((symval >= gp
>>>>>> +                  && VALID_ITYPE_IMM (symval - gp + max_alignment + reserve_size))
>>>>>> +                 || (symval < gp
>>>>>> +                     && VALID_ITYPE_IMM (symval - gp - max_alignment - reserve_size))))))
>>>>>>        {
>>>>>>          unsigned sym = ELFNN_R_SYM (rel->r_info);
>>>>>>          switch (ELFNN_R_TYPE (rel->r_info))
>>>>>> --
>>>>>> 2.6.0-rc0
>>>>>>
>> I haven't looked into the details.
>> .text < DATA_SEGMENT_ALIGN < .sdata < DATA_SEGMENT_RELRO_END
>>
>> If gp relaxation requires that ld estimates the distance between the
>> relocated location and .sdata, being conservative and assuming
>> DATA_SEGMENT_ALIGN+DATA_SEGMENT_RELRO_END may take
>> maxpagesize+commonpagesize bytes looks good to me.
>>
>> LLD avoids the DATA_SEGMENT_ALIGN/DATA_SEGMENT_RELRO_END complexity by
>> having 2 RW segments and making the first RW overlap with PT_GNU_RELRO
>> (https://reviews.llvm.org/D58892).