COMMITTED: Add support for STT_IFUNC

[Nick Clifton]

Hi Guys,

  I am applying the patch below to add support for a new ELF symbol
  type.  It is currently under review by the ELF committee and I am
  reliably informed that it will be added to the official
  specification fairly soon now.  This is what the specification looks
  like:

    STT_IFUNC
 
      This symbol type is the same as STT_IFUNC except that it always
      points to a function or piece of executable code which takes no
      arguments and which returns a function pointer.  If an STT_IFUNC
      symbol is referred to by a relocation then evaluation of that
      relocation is delayed until load-time.  The value used in the
      relocation is the function pointer returned by an invocation
      of the STT_IFUNC symbol.
 
      The purpose of this symbol type is it to allow the run-time to
      select between multiple versions of the implementation of a
      specific function.  The selection made in general will take the
      currently available hardware into account and select the most
      appropriate version.
  
  So this patch adds support for this symbol type to the assembler
  (via ".type <foo>, %STT_IFUNC"), the linker and the binutils.
  Currently linker support has only been added for the x86 and x86_64
  targets, but it can easily be extended to other targets that might
  wish to use it.

  Run-time relocations against this symbol type are placed into a new
  section called .rel[a].ifunc.dyn which immediately follows the
  .rel[a].dyn section.  The idea here is to allow the dynamic linker
  to execute all of the normal dynamic relocations first, before it
  tries to execute any of the STT_IFUNC using dynamic relocs.  This is
  just in case the invoked STT_IFUNC function has any dependencies
  upon other symbols.

  Readelf, nm and objdump have been extended to display the new symbol
  type.  Objdump and nm use the letter 'i' to indicate the new
  symbol type, eg:
  
     080484c0 g   i   .text  00000024              ifunction

  whereas readelf uses IFUNC:
  
     7: 080484c0    36 IFUNC   GLOBAL DEFAULT   14 ifunction
     
  Plus objdump and readelf will append "()" to relocs which are made
  against STT_IFUNC symbols, as a hint that the relocation invokes a
  function:

    RELOCATION RECORDS FOR [.text]:
    OFFSET   TYPE              VALUE 
    00000009 R_386_32          .rodata
    0000009f R_386_PC32        ifunction() 

  Tested against all sorts of toolchains without any regressions.

Cheers
  Nick

include/elf/ChangeLog
2008-12-03  Nick Clifton  <nickc@redhat.com>

	* common.h (STT_IFUNC): Define.

elfcpp/ChangeLog
2008-12-03  Nick Clifton  <nickc@redhat.com>

	* elfcpp.h (enum STT): Add STT_IFUNC.

bfd/ChangeLog
2008-12-03  Nick Clifton  <nickc@redhat.com>

	* syms.c (struct bfd_symbol): Add new flag BSF_INDIRECT_FUNCTION.
	Remove redundant flag BFD_FORT_COMM_DEFAULT_VALUE.  Renumber flags
	to remove gaps.
	(bfd_print_symbol_vandf): Return 'i' for BSF_INDIRECT_FUNCTION.
	(bfd_decode_symclass): Likewise.
	* elf.c (swap_out_syms): Translate BSF_INDIRECT_FUNCTION into
	STT_IFUNC.
	(elf_find_function): Treat STT_IFUNC in the same way as STT_FUNC.
	(_bfd_elf_is_function_type): Likewise.
	* elf32-arm.c (arm_elf_find_function): Likewise.
	(elf32_arm_adjust_dynamic_symbol): Likewise.
	(elf32_arm_swap_symbol_in): Likewise.
	(elf32_arm_additional_program_headers): Likewise.
	* elf32-i386.c (is_indirect_symbol): New function.
	(elf_i386_check_relocs): Also generate dynamic relocs for
	relocations against STT_IFUNC symbols.
	(allocate_dynrelocs): Likewise.
	(elf_i386_relocate_section): Likewise.
	* elf64-x86-64.c (is_indirect_symbol): New function.
	(elf64_x86_64_check_relocs): Also generate dynamic relocs for
	relocations against STT_IFUNC symbols.
	(allocate_dynrelocs): Likewise.
	(elf64_x86_64_relocate_section): Likewise.
	* elfcode.h (elf_slurp_symbol_table): Translate STT_IFUNC into
	BSF_INDIRECT_FUNCTION.
	* elflink.c (_bfd_elf_adjust_dynamic_reloc_section): Add support
	for STT_IFUNC symbols.
	(get_ifunc_reloc_section_name): New function.
	(_bfd_elf_make_ifunc_reloc_section): New function.
	* elf-bfd.h (struct bfd_elf_section_data): Add indirect_relocs field.
	* bfd-in2.h: Regenerate.

gas/ChangeLog
2008-12-03  Nick Clifton  <nickc@redhat.com>

	* config/obj-elf.c (obj_elf_type): Add support for STT_IFUNC type.
	* doc/as.texinfo: Document new feature.
	* NEWS: Mention new feature.

gas/testsuite/ChangeLog
2008-12-03  Nick Clifton  <nickc@redhat.com>

	* gas/elf/type.s: Add test of STT_IFUNC symbol type.
	* gas/elf/type.e: Update expected disassembly.
	* gas/elf/elf.exp: Update grep of symbol types.

ld/ChangeLog
2008-12-03  Nick Clifton  <nickc@redhat.com>

	* NEWS: Mention new feature.
	* NEWS: Mention new feature.
	* pe-dll.c (process_def_file): Replace use of redundant
	BFD_FORT_COMM_DEFAULT_VALUE with 0.
	* scripttempl/elf.sc: Add .rel.ifunc.dyn and .rela.ifunc.dyn
	sections.

ld/testsuite/ChangeLog
2008-12-03  Nick Clifton  <nickc@redhat.com>

	* ld-mips-elf/reloc-1-n32.d: Updated expected output for reloc
	descriptions.
	* ld-mips-elf/reloc-1-n64.d: Likewise.
	* ld-i386/ifunc.d: New test.
	* ld-i386/ifunc.s: Source file for the new test.
	* ld-i386/i386.exp: Run the new test.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: ifunc.patch
Type: text/x-patch
Size: 62682 bytes
Desc: not available
URL: <https://sourceware.org/pipermail/binutils/attachments/20081203/d7353052/attachment.bin>