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author | Sriraman Tallam <tmsriram@google.com> | 2016-06-28 15:42:33 -0700 |
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committer | Sriraman Tallam <tmsriram@google.com> | 2016-06-28 15:42:33 -0700 |
commit | 3a4f096e5ff41e2a3b832cf6c815ad1f28437c63 (patch) | |
tree | 4b687f6684621526904028771534d04e5da2f0bf /gold/x86_64.cc | |
parent | 8032ac03390ca5bc33f8efe29447d0a4bc492950 (diff) | |
download | binutils-gdb-3a4f096e5ff41e2a3b832cf6c815ad1f28437c63.tar.gz |
Convert indirect calls to direct when possible.
Please see patch discussion:
https://www.sourceware.org/ml/binutils/2016-05/msg00322.html
2016-06-28 Sriraman Tallam <tmsriram@google.com>
* x86_64.cc (Lazy_view): New class.
(can_convert_mov_to_lea): Templatize function. Make the function
check for appropriate relocation types and use the view parameter
to get section contents.
(can_convert_callq_to_direct): New function.
(Target_x86_64<size>::Scan::global): Refactor.
(Target_x86_64<size>::Relocate::relocate): Refactor. Change any indirect
call via GOT that can be converted.
* testsuite/Makefile.am (x86_64_indirect_call_to_direct.sh): New test.
* testsuite/Makefile.in: Regenerate.
* testsuite/x86_64_indirect_call_to_direct1.s: New file.
* testsuite/x86_64_indirect_jump_to_direct1.s: New file.
Diffstat (limited to 'gold/x86_64.cc')
-rw-r--r-- | gold/x86_64.cc | 172 |
1 files changed, 144 insertions, 28 deletions
diff --git a/gold/x86_64.cc b/gold/x86_64.cc index d069957f5b9..6c511e2b607 100644 --- a/gold/x86_64.cc +++ b/gold/x86_64.cc @@ -403,6 +403,33 @@ class Output_data_plt_x86_64_standard : public Output_data_plt_x86_64<size> static const unsigned char plt_eh_frame_fde[plt_eh_frame_fde_size]; }; +template<int size> +class Lazy_view +{ + public: + Lazy_view(Sized_relobj_file<size, false>* object, unsigned int data_shndx) + : object_(object), data_shndx_(data_shndx), view_(NULL), view_size_(0) + { } + + inline unsigned char + operator[](size_t offset) + { + if (this->view_ == NULL) + this->view_ = this->object_->section_contents(this->data_shndx_, + &this->view_size_, + true); + if (offset >= this->view_size_) + return 0; + return this->view_[offset]; + } + + private: + Sized_relobj_file<size, false>* object_; + unsigned int data_shndx_; + const unsigned char* view_; + section_size_type view_size_; +}; + // The x86_64 target class. // See the ABI at // http://www.x86-64.org/documentation/abi.pdf @@ -876,19 +903,62 @@ class Target_x86_64 : public Sized_target<size, false> // conversion from // mov foo@GOTPCREL(%rip), %reg // to lea foo(%rip), %reg. - static bool - can_convert_mov_to_lea(const Symbol* gsym) + template<class View_type> + static inline bool + can_convert_mov_to_lea(const Symbol* gsym, unsigned int r_type, + size_t r_offset, View_type* view) { gold_assert(gsym != NULL); - return (gsym->type() != elfcpp::STT_GNU_IFUNC - && !gsym->is_undefined () - && !gsym->is_from_dynobj() - && !gsym->is_preemptible() - && (!parameters->options().shared() - || (gsym->visibility() != elfcpp::STV_DEFAULT - && gsym->visibility() != elfcpp::STV_PROTECTED) - || parameters->options().Bsymbolic()) - && strcmp(gsym->name(), "_DYNAMIC") != 0); + // We cannot do the conversion unless it's one of these relocations. + if (r_type != elfcpp::R_X86_64_GOTPCREL + && r_type != elfcpp::R_X86_64_GOTPCRELX + && r_type != elfcpp::R_X86_64_REX_GOTPCRELX) + return false; + // We cannot convert references to IFUNC symbols, or to symbols that + // are not local to the current module. + if (gsym->type() == elfcpp::STT_GNU_IFUNC + || gsym->is_undefined () + || gsym->is_from_dynobj() + || gsym->is_preemptible()) + return false; + // If we are building a shared object and the symbol is protected, we may + // need to go through the GOT. + if (parameters->options().shared() + && gsym->visibility() == elfcpp::STV_PROTECTED) + return false; + // We cannot convert references to the _DYNAMIC symbol. + if (strcmp(gsym->name(), "_DYNAMIC") == 0) + return false; + // Check for a MOV opcode. + return (*view)[r_offset - 2] == 0x8b; + } + + // Convert + // callq *foo@GOTPCRELX(%rip) to + // addr32 callq foo + // and jmpq *foo@GOTPCRELX(%rip) to + // jmpq foo + // nop + template<class View_type> + static inline bool + can_convert_callq_to_direct(const Symbol* gsym, unsigned int r_type, + size_t r_offset, View_type* view) + { + gold_assert(gsym != NULL); + // We cannot do the conversion unless it's a GOTPCRELX relocation. + if (r_type != elfcpp::R_X86_64_GOTPCRELX) + return false; + // We cannot convert references to IFUNC symbols, or to symbols that + // are not local to the current module. + if (gsym->type() == elfcpp::STT_GNU_IFUNC + || gsym->is_undefined () + || gsym->is_from_dynobj() + || gsym->is_preemptible()) + return false; + // Check for a CALLQ or JMPQ opcode. + return ((*view)[r_offset - 2] == 0xff + && ((*view)[r_offset - 1] == 0x15 + || (*view)[r_offset - 1] == 0x25)); } // Adjust TLS relocation type based on the options and whether this @@ -2935,19 +3005,24 @@ Target_x86_64<size>::Scan::global(Symbol_table* symtab, // If we convert this from // mov foo@GOTPCREL(%rip), %reg // to lea foo(%rip), %reg. + // OR + // if we convert + // (callq|jmpq) *foo@GOTPCRELX(%rip) to + // (callq|jmpq) foo // in Relocate::relocate, then there is nothing to do here. - if ((r_type == elfcpp::R_X86_64_GOTPCREL - || r_type == elfcpp::R_X86_64_GOTPCRELX - || r_type == elfcpp::R_X86_64_REX_GOTPCRELX) - && 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; - } + + Lazy_view<size> view(object, data_shndx); + size_t r_offset = reloc.get_r_offset(); + if (r_offset >= 2 + && Target_x86_64<size>::can_convert_mov_to_lea(gsym, r_type, + r_offset, &view)) + break; + + if (r_offset >= 2 + && Target_x86_64<size>::can_convert_callq_to_direct(gsym, r_type, + r_offset, + &view)) + break; if (gsym->final_value_is_known()) { @@ -3629,15 +3704,56 @@ Target_x86_64<size>::Relocate::relocate( // mov foo@GOTPCREL(%rip), %reg // to lea foo(%rip), %reg. // if possible. - if (rela.get_r_offset() >= 2 - && view[-2] == 0x8b - && ((gsym == NULL && !psymval->is_ifunc_symbol()) - || (gsym != NULL - && Target_x86_64<size>::can_convert_mov_to_lea(gsym)))) + if ((gsym == NULL + && rela.get_r_offset() >= 2 + && view[-2] == 0x8b + && !psymval->is_ifunc_symbol()) + || (gsym != NULL + && rela.get_r_offset() >= 2 + && Target_x86_64<size>::can_convert_mov_to_lea(gsym, r_type, + 0, &view))) { view[-2] = 0x8d; Reloc_funcs::pcrela32(view, object, psymval, addend, address); } + // Convert + // callq *foo@GOTPCRELX(%rip) to + // addr32 callq foo + // and jmpq *foo@GOTPCRELX(%rip) to + // jmpq foo + // nop + else if (gsym != NULL + && rela.get_r_offset() >= 2 + && Target_x86_64<size>::can_convert_callq_to_direct(gsym, + r_type, + 0, &view)) + { + if (view[-1] == 0x15) + { + // Convert callq *foo@GOTPCRELX(%rip) to addr32 callq. + // Opcode of addr32 is 0x67 and opcode of direct callq is 0xe8. + view[-2] = 0x67; + view[-1] = 0xe8; + // Convert GOTPCRELX to 32-bit pc relative reloc. + Reloc_funcs::pcrela32(view, object, psymval, addend, address); + } + else + { + // Convert jmpq *foo@GOTPCRELX(%rip) to + // jmpq foo + // nop + // The opcode of direct jmpq is 0xe9. + view[-2] = 0xe9; + // The opcode of nop is 0x90. + view[3] = 0x90; + // Convert GOTPCRELX to 32-bit pc relative reloc. jmpq is rip + // relative and since the instruction following the jmpq is now + // the nop, offset the address by 1 byte. The start of the + // relocation also moves ahead by 1 byte. + Reloc_funcs::pcrela32(&view[-1], object, psymval, addend, + address - 1); + } + } else { if (gsym != NULL) |