[PATCH] PR gold/18609

[H.J. Lu]

On Mon, Jul 20, 2015 at 8:24 AM, Andrew Senkevich
<andrew.n.senkevich@gmail.com> wrote:
>>> diff --git a/gold/x86_64.cc b/gold/x86_64.cc
>>> index 007af1d..8f53bfc 100644
>>> --- a/gold/x86_64.cc
>>> +++ b/gold/x86_64.cc
>>> @@ -2480,23 +2480,6 @@ Target_x86_64<size>::Scan::local(Symbol_table* symtab,
>>>         // The symbol requires a GOT section.
>>>         Output_data_got<64, false>* got = target->got_section(symtab, layout);
>>>
>>> -       // If the relocation symbol isn't IFUNC,
>>> -       // and is local, then we will convert
>>> -       // mov foo@GOTPCREL(%rip), %reg
>>> -       // to lea foo(%rip), %reg.
>>> -       // in Relocate::relocate.
>>> -       if (r_type == elfcpp::R_X86_64_GOTPCREL
>>> -           && reloc.get_r_offset() >= 2
>>> -           && !is_ifunc)
>>> -         {
>>> -           section_size_type stype;
>>> -           const unsigned char* view = object->section_contents(data_shndx,
>>> -                                                                &stype, true);
>>> -           if (view[reloc.get_r_offset() - 2] == 0x8b)
>>> -             break;
>>> -         }
>>> -
>>> -
>>>         // The symbol requires a GOT entry.
>>>         unsigned int r_sym = elfcpp::elf_r_sym<size>(reloc.get_r_info());
>>>
>>> @@ -2906,21 +2889,6 @@ Target_x86_64<size>::Scan::global(Symbol_table* symtab,
>>>         // The symbol requires a GOT entry.
>>>         Output_data_got<64, false>* got = target->got_section(symtab, layout);
>>>
>>> -       // If we convert this from
>>> -       // mov foo@GOTPCREL(%rip), %reg
>>> -       // to lea foo(%rip), %reg.
>>> -       // in Relocate::relocate, then there is nothing to do here.
>>> -       if (r_type == elfcpp::R_X86_64_GOTPCREL
>>> -           && reloc.get_r_offset() >= 2
>>> -           && Target_x86_64<size>::can_convert_mov_to_lea(gsym))
>>> -         {
>>> -           section_size_type stype;
>>> -           const unsigned char* view = object->section_contents(data_shndx,
>>> -                                                                &stype, true);
>>> -           if (view[reloc.get_r_offset() - 2] == 0x8b)
>>> -             break;
>>> -         }
>>> -
>>
>> If you remove those changes, won't it generate an unused GOT slot
>> when GOTPCREL relocation is converted to PC-relative relocation?
>
> Yes, it can generate unused GOT slots.
>

I think we should add a testcase to check for the unused GOT slot.
Please check if you can implement similar heuristic in gold:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=59cab532835904f368b0aa99267afba5fda5ded2

-- 
H.J.