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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: ccoutant at gmail dot com
- Date: Wed, 2 Dec 2015 10:17:52 -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>
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
>