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Re: [GOLD] PowerPC TLS fixes
On Wed, Sep 12, 2012 at 10:06 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Wed, Sep 12, 2012 at 9:58 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Sun, Sep 9, 2012 at 7:42 AM, Alan Modra <amodra@gmail.com> wrote:
>>> This patch corrects TLS GOT entries for powerpc. We were generating
>>> unnecessary relocations for symbols that resolve locally, and TLSGD
>>> module/offset GOT entries were just plain wrong. TLSGD entries for
>>> local symbols consist of two words, the first value doesn't matter but
>>> this word needs a DTPMOD dynamic relocation against any local tls
>>> symbol or even the zero index symbol. The second word is the DTPREL
>>> offset for the local symbol, a constant, but powerpc differs from
>>> other targets in that the dynamic thread pointer is offset by 0x8000.
>>> A DTPREL relocation thus evaluates to the symbol value minus 0x8000.
>>> If we remove all the unnecessary relocations then we also need to
>>> support TPREL GOT entries. These also are offset, but by 0x7000.
>>>
>>> Offsets from the symbol are not supported by current gold GOT handling
>>> infrastructure, and trying to use the typical BFD scheme of
>>> initializing the .got section entries while relocating other sections
>>> isn't a good idea when section relocation happens in parallel. I
>>> originally thought I'd need to crib another bit from Got_entry
>>> local_sym_index_, but then realized a tls symbol will never need a plt
>>> offset, so we can use that bit to signify a target dependent offset.
>>>
>>> I also tidy the existing add_local_pair_with_rel. No target uses the
>>> second reloc, and I can't see any possible use of a DTP relative reloc
>>> against an output section symbol. A DTP relative reloc in a tls_index
>>> (module/offset) entry always refers to the symbol of interest in the
>>> associated __tls_get_addr call (contrasted to the module reloc which
>>> ought to be happy with any symbol in the same object).
>>>
>>> OK, to apply?
>>>
>>> * output.h (Output_data_got::add_global_tls, add_local_tls,
>>> add_local_tls_pair): New functions.
>>> (Output_data_got::add_local_pair_with_rel): Remove second
>>> reloc param. Expand comment.
>>> (Output_data_got::Got_entry::write): Add got_index param.
>>> * output.cc (Output_data_got::add_global_tls, add_local_tls,
>>> add_local_tls_pair): New functions.
>>> (Output_data_got::Got_entry::write): Handle tls symbols
>>> with use_plt_offset_ set specially.
>>> (Output_data_got::add_local_pair_with_rel): Only one reloc.
>>> (Output_data_got::do_write): Replace iterator with index, pass
>>> index to entry write function.
>>> * target.h (Target::tls_offset_for_local, tls_offset_for_global,
>>> do_tls_offset_for_local, do_tls_offset_for_global): New functions.
>>> * arm.cc (Target_arm::Scan::local): Update add_local_pair_with_rel
>>> call.
>>> * i386.cc (Target_i386::Scan::local): Likewise.
>>> * sparc.cc (Target_sparc::Scan::local): Likewise.
>>> * x86_64.cc (Target_x86_64::Scan::local): Likewise.
>>> * powerpc.cc (Target_powerpc::do_tls_offset_for_local,
>>> do_tls_offset_for_global): New functions.
>>> (Target_powerpc::Scan::local): Correct TLS relocations and got
>>> entry values.
>>> (Target_powerpc::Scan::global): Don't emit unnecessary
>>> dynamic relocations on TLS GOT entries.
>>>
>>
>>>
>>> Index: gold/output.cc
>>> ===================================================================
>>> RCS file: /cvs/src/src/gold/output.cc,v
>>> retrieving revision 1.171
>>> diff -u -p -r1.171 output.cc
>>> --- gold/output.cc 5 Sep 2012 00:34:20 -0000 1.171
>>> +++ gold/output.cc 9 Sep 2012 11:45:27 -0000
>>> @@ -1369,7 +1369,9 @@ Output_data_group<size, big_endian>::do_
>>>
>>> template<int size, bool big_endian>
>>> void
>>> -Output_data_got<size, big_endian>::Got_entry::write(unsigned char* pov) const
>>> +Output_data_got<size, big_endian>::Got_entry::write(
>>> + unsigned int got_indx,
>>> + unsigned char* pov) const
>>> {
>>> Valtype val = 0;
>>>
>>> @@ -1392,6 +1394,9 @@ Output_data_got<size, big_endian>::Got_e
>>> // as small as possible.
>>> sgsym = static_cast<Sized_symbol<size>*>(gsym);
>>> val = sgsym->value();
>>> + if (this->use_plt_offset_ && gsym->type() == elfcpp::STT_TLS)
>>> + val += parameters->target().tls_offset_for_global(gsym,
>>> + got_indx);
>>> }
>>> }
>>> break;
>>> @@ -1409,19 +1414,24 @@ Output_data_got<size, big_endian>::Got_e
>>>
>>> default:
>>> {
>>> - const Relobj* object = this->u_.object;
>>> + const Sized_relobj_file<size, big_endian>* object
>>> + = static_cast<Sized_relobj_file<size, big_endian>*>(this->u_.object);
>>> const unsigned int lsi = this->local_sym_index_;
>>
>> This breaks x32. X32 uses 32-bit ELF format with 64-bit GOT entry.
>>
>> H.J.
>
> Output_data_got is declared as:
>
> template<int got_size, bool big_endian>
> class Output_data_got : public Output_data_got_base
> {
> public:
> typedef typename elfcpp::Elf_types<got_size>::Elf_Addr Valtype;
>
> The template size parameter is for GOT size, which
> is independent of the template size parameter for
>
> // A regular object file. This is size and endian specific.
>
> template<int size, bool big_endian>
> class Sized_relobj_file : public Sized_relobj<size, big_endian>
> {
>
> Ian, how should we fix it?
>
I opened:
http://www.sourceware.org/bugzilla/show_bug.cgi?id=14570
--
H.J.