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Re: [PATCH] gold: Implement --long-plt flag.
- From: Peter Collingbourne <pcc at google dot com>
- To: binutils at sourceware dot org
- Cc: Cary Coutant <ccoutant at gmail dot com>
- Date: Mon, 14 Dec 2015 10:28:13 -0800
- Subject: Re: [PATCH] gold: Implement --long-plt flag.
- Authentication-results: sourceware.org; auth=none
- References: <1448063109-18860-1-git-send-email-pcc at google dot com> <CAMn1gO5KQP_zVmbuJLNtFO1JJ39Fn=4SvbHC=HrG4uWtp6GHKQ at mail dot gmail dot com>
Ping^2.
On Wed, Dec 2, 2015 at 10:17 AM, Peter Collingbourne <pcc@google.com> wrote:
> Ping.
>
> On Fri, Nov 20, 2015 at 3:45 PM, Peter Collingbourne <pcc@google.com> wrote:
>> gold/
>> PR gold/18780
>> * arm.cc (Target_arm::do_make_data_plt): Choose PLT generator based
>> on value of --long-plt flag.
>> (Output_data_plt_arm_standard::do_get_plt_entry_size): Moved to
>> Output_data_plt_arm_short.
>> (Output_data_plt_arm_standard::do_fill_plt_entry): Likewise.
>> (Output_data_plt_arm_standard::plt_entry): Likewise.
>> (Output_data_plt_arm_standard::do_fill_first_plt_entry): Fix
>> variable reference.
>> (Output_data_plt_arm_short): New class.
>> (Output_data_plt_arm_long): New class.
>> * options.h (General_options): Define --long-plt flag.
>> ---
>> gold/arm.cc | 124 +++++++++++++++++++++++++++++++++++++++++++++++----------
>> gold/options.h | 4 ++
>> 2 files changed, 108 insertions(+), 20 deletions(-)
>>
>> diff --git a/gold/arm.cc b/gold/arm.cc
>> index 4a6d414..2381442 100644
>> --- a/gold/arm.cc
>> +++ b/gold/arm.cc
>> @@ -62,7 +62,10 @@ template<bool big_endian>
>> class Output_data_plt_arm;
>>
>> template<bool big_endian>
>> -class Output_data_plt_arm_standard;
>> +class Output_data_plt_arm_short;
>> +
>> +template<bool big_endian>
>> +class Output_data_plt_arm_long;
>>
>> template<bool big_endian>
>> class Stub_table;
>> @@ -2555,7 +2558,11 @@ class Target_arm : public Sized_target<32, big_endian>
>> Output_data_space* got_irelative)
>> {
>> gold_assert(got_plt != NULL && got_irelative != NULL);
>> - return new Output_data_plt_arm_standard<big_endian>(
>> + if (parameters->options().long_plt())
>> + return new Output_data_plt_arm_long<big_endian>(
>> + layout, got, got_plt, got_irelative);
>> + else
>> + return new Output_data_plt_arm_short<big_endian>(
>> layout, got, got_plt, got_irelative);
>> }
>>
>> @@ -7719,29 +7726,14 @@ class Output_data_plt_arm_standard : public Output_data_plt_arm<big_endian>
>> do_first_plt_entry_offset() const
>> { return sizeof(first_plt_entry); }
>>
>> - // Return the size of a PLT entry.
>> - virtual unsigned int
>> - do_get_plt_entry_size() const
>> - { return sizeof(plt_entry); }
>> -
>> virtual void
>> do_fill_first_plt_entry(unsigned char* pov,
>> Arm_address got_address,
>> Arm_address plt_address);
>>
>> - virtual void
>> - do_fill_plt_entry(unsigned char* pov,
>> - Arm_address got_address,
>> - Arm_address plt_address,
>> - unsigned int got_offset,
>> - unsigned int plt_offset);
>> -
>> private:
>> // Template for the first PLT entry.
>> static const uint32_t first_plt_entry[5];
>> -
>> - // Template for subsequent PLT entries.
>> - static const uint32_t plt_entry[3];
>> };
>>
>> // ARM PLTs.
>> @@ -7769,7 +7761,7 @@ Output_data_plt_arm_standard<big_endian>::do_fill_first_plt_entry(
>> {
>> // Write first PLT entry. All but the last word are constants.
>> const size_t num_first_plt_words = (sizeof(first_plt_entry)
>> - / sizeof(plt_entry[0]));
>> + / sizeof(first_plt_entry[0]));
>> for (size_t i = 0; i < num_first_plt_words - 1; i++)
>> elfcpp::Swap<32, big_endian>::writeval(pov + i * 4, first_plt_entry[i]);
>> // Last word in first PLT entry is &GOT[0] - .
>> @@ -7778,9 +7770,39 @@ Output_data_plt_arm_standard<big_endian>::do_fill_first_plt_entry(
>> }
>>
>> // Subsequent entries in the PLT.
>> +// This class generates short (12-byte) entries, for displacements up to 2^28.
>>
>> template<bool big_endian>
>> -const uint32_t Output_data_plt_arm_standard<big_endian>::plt_entry[3] =
>> +class Output_data_plt_arm_short : public Output_data_plt_arm_standard<big_endian>
>> +{
>> + public:
>> + Output_data_plt_arm_short(Layout* layout,
>> + Arm_output_data_got<big_endian>* got,
>> + Output_data_space* got_plt,
>> + Output_data_space* got_irelative)
>> + : Output_data_plt_arm_standard<big_endian>(layout, got, got_plt, got_irelative)
>> + { }
>> +
>> + protected:
>> + // Return the size of a PLT entry.
>> + virtual unsigned int
>> + do_get_plt_entry_size() const
>> + { return sizeof(plt_entry); }
>> +
>> + virtual void
>> + do_fill_plt_entry(unsigned char* pov,
>> + Arm_address got_address,
>> + Arm_address plt_address,
>> + unsigned int got_offset,
>> + unsigned int plt_offset);
>> +
>> + private:
>> + // Template for subsequent PLT entries.
>> + static const uint32_t plt_entry[3];
>> +};
>> +
>> +template<bool big_endian>
>> +const uint32_t Output_data_plt_arm_short<big_endian>::plt_entry[3] =
>> {
>> 0xe28fc600, // add ip, pc, #0xNN00000
>> 0xe28cca00, // add ip, ip, #0xNN000
>> @@ -7789,7 +7811,7 @@ const uint32_t Output_data_plt_arm_standard<big_endian>::plt_entry[3] =
>>
>> template<bool big_endian>
>> void
>> -Output_data_plt_arm_standard<big_endian>::do_fill_plt_entry(
>> +Output_data_plt_arm_short<big_endian>::do_fill_plt_entry(
>> unsigned char* pov,
>> Arm_address got_address,
>> Arm_address plt_address,
>> @@ -7808,6 +7830,68 @@ Output_data_plt_arm_standard<big_endian>::do_fill_plt_entry(
>> elfcpp::Swap<32, big_endian>::writeval(pov + 8, plt_insn2);
>> }
>>
>> +// This class generates long (16-byte) entries, for arbitrary displacements.
>> +
>> +template<bool big_endian>
>> +class Output_data_plt_arm_long : public Output_data_plt_arm_standard<big_endian>
>> +{
>> + public:
>> + Output_data_plt_arm_long(Layout* layout,
>> + Arm_output_data_got<big_endian>* got,
>> + Output_data_space* got_plt,
>> + Output_data_space* got_irelative)
>> + : Output_data_plt_arm_standard<big_endian>(layout, got, got_plt, got_irelative)
>> + { }
>> +
>> + protected:
>> + // Return the size of a PLT entry.
>> + virtual unsigned int
>> + do_get_plt_entry_size() const
>> + { return sizeof(plt_entry); }
>> +
>> + virtual void
>> + do_fill_plt_entry(unsigned char* pov,
>> + Arm_address got_address,
>> + Arm_address plt_address,
>> + unsigned int got_offset,
>> + unsigned int plt_offset);
>> +
>> + private:
>> + // Template for subsequent PLT entries.
>> + static const uint32_t plt_entry[4];
>> +};
>> +
>> +template<bool big_endian>
>> +const uint32_t Output_data_plt_arm_long<big_endian>::plt_entry[4] =
>> +{
>> + 0xe28fc200, // add ip, pc, #0xN0000000
>> + 0xe28cc600, // add ip, ip, #0xNN00000
>> + 0xe28cca00, // add ip, ip, #0xNN000
>> + 0xe5bcf000, // ldr pc, [ip, #0xNNN]!
>> +};
>> +
>> +template<bool big_endian>
>> +void
>> +Output_data_plt_arm_long<big_endian>::do_fill_plt_entry(
>> + unsigned char* pov,
>> + Arm_address got_address,
>> + Arm_address plt_address,
>> + unsigned int got_offset,
>> + unsigned int plt_offset)
>> +{
>> + int32_t offset = ((got_address + got_offset)
>> + - (plt_address + plt_offset + 8));
>> +
>> + uint32_t plt_insn0 = plt_entry[0] | (offset >> 28);
>> + elfcpp::Swap<32, big_endian>::writeval(pov, plt_insn0);
>> + uint32_t plt_insn1 = plt_entry[1] | ((offset >> 20) & 0xff);
>> + elfcpp::Swap<32, big_endian>::writeval(pov + 4, plt_insn1);
>> + uint32_t plt_insn2 = plt_entry[2] | ((offset >> 12) & 0xff);
>> + elfcpp::Swap<32, big_endian>::writeval(pov + 8, plt_insn2);
>> + uint32_t plt_insn3 = plt_entry[3] | (offset & 0xfff);
>> + elfcpp::Swap<32, big_endian>::writeval(pov + 12, plt_insn3);
>> +}
>> +
>> // Write out the PLT. This uses the hand-coded instructions above,
>> // and adjusts them as needed. This is all specified by the arm ELF
>> // Processor Supplement.
>> diff --git a/gold/options.h b/gold/options.h
>> index ffc44e6..d83ea54 100644
>> --- a/gold/options.h
>> +++ b/gold/options.h
>> @@ -834,6 +834,10 @@ class General_options
>> "veneer"),
>> NULL);
>>
>> + DEFINE_bool(long_plt, options::TWO_DASHES, '\0', false,
>> + N_("(ARM only) Generate long PLT entries."),
>> + N_("(ARM only) Do not generate long PLT entries."));
>> +
>> DEFINE_bool(g, options::EXACTLY_ONE_DASH, '\0', false,
>> N_("Ignored"), NULL);
>>
>> --
>> 2.6.0.rc2.230.g3dd15c0
>>