binutils

Upstream webpage: http://sources.redhat.com/binutils

Binutils contains the GNU assembler, linker and binary utilities. For PA-RISC, binutils supports several targets, including hppa-linux, hppa64-linux, hppa-netbsd, hppa-hpux, hppa64-hpux.

BFD

A large part of binutils is the “bfd” library. According to the README that comes with bfd:

BFD is an object file library.  It permits applications to use the
same routines to process object files regardless of their format.

BFD is used by the GNU debugger, assembler, linker, and the binary
utilities.

The documentation on using BFD is scanty and may be occasionally
incorrect.  Pointers to documentation problems, or an entirely
rewritten manual, would be appreciated.

Sigh…

The interesting files for this port are:

  • bfd/elf-hppa.h

  • bfd/elf32-hppa.[ch]

  • bfd/elf64-hppa.[ch]

  • bfd/libhppa.h

  • include/elf/hppa.h

One of the wishlist TODO items is to merge the 32 and 64-bit implementations into a single file, so that it can be maintained more easily. Currently there is quite a bit of overlap, but also a lot of differences between the two targets.

bfd/elf32.hppa.c

Data structures:

elf32_hppa_link_hash_table is derived from elf_link_hash_table. It is passed around to most of the linker functions (usually as a parameter called info). “Global” data is placed in this structure.

elf32_hppa_link_hash_entry is derived from elf_link_hash_entry. One of these are created for each dynamic symbol.

Embedded in the elf32_hppa_link_hash_table is a generic ELF hash table stub_hash_table. This is used to hold information about a variety of linker-generated stubs.

On hppa-linux, the following stub types are used:

  • Long branch stub: used when a branch (R_PARISC_PCREL17F or R_PARISC_PCREL22F) cannot reach its destination (non-PIC and PIC versions)

  • Import stub: used to call a shared library function. There is one version for calling a sharedlib function from other sharedlib, and another for calling a sharedlib function from an executable.

Since hppa-linux doesn’t support multiple subspaces, we do not need export stubs.

TODO: put call sequence here

  • elf32_hppa_link_hash_table_create - create the link hash table structure

  • elf32_hppa_create_dynamic_sections - create the .got and .plt sections, and possibly .dynamic

  • elf32_hppa_copy_indirect_symbol

  • elf32_hppa_check_relocs - Do some preliminary checks on relocs, if needed allocate space for local GOT/PLT entries, do some checking on TLS references

  • elf32_hppa_gc_mark_hook

  • elf32_hppa_gc_sweep_hook

  • elf32_hppa_hide_symbol

  • elf32_hppa_adjust_dynamic_symbol

  • elf32_hppa_size_dynamic_sections

    • allocate_plt_static

    • allocate_dynrelocs

    • clobber_millicode_symbols

    • readonly_dynrelocs

  • elf32_hppa_setup_section_lists

  • elf32_hppa_next_input_section

    • elf32_hppa_size_stubs

    • group_sections

    • get_local_syms

  • elf32_hppa_set_gp

  • elf32_hppa_build_stubs

  • elf32_hppa_final_link

  • elf32_hppa_relocate_section

    • hppa_record_segment_addr

    • final_link_relocate

  • elf32_hppa_finish_dynamic_symbol

  • elf32_hppa_reloc_type_class

  • elf32_hppa_finish_dynamic_sections

  • elf32_hppa_post_process_headers

  • elf32_hppa_elf_get_symbol_type

bfd/elf64-hppa.c

TODO: put call sequence here

Assembler (gas)

The interesting files for this port are:

  • gas/config/tc-hppa.c

  • gas/config/tc-hppa.h

  • include/opcode/hppa.h: description of all the insns

  • include/elf/hppa.h: ELF constants

Linker (ld)

The gnu linker is an interesting piece of software that uses a weird combination of templates to generate a working cross linker. I still don’t fully understand all this.

Files of interest are:

  • ld/emultmpl/hppaelf.em

  • ld/emulparams/hppaelf.sh

  • ld/emulparams/hppalinux.sh

There a number of other files that might be of interest, including the elf64 stuff:

  • ld/emulparams/elf64hppa.sh

  • ld/emulparams/hppa64linux.sh

TODO: The 64-bit linker doesn’t have multiple stub sections. Therefore the stub might not be able to reach the intended target if the distance is too large. We need to add multiple stub section support for the 64-bit linker.

Should trace the linker function calls in order to determine how the mechanics work for 32-bit.

For example, for 32-bit from the ld/emultmpl/hppaelf.em definition we will call:

gld${EMULATION_NAME}_finish (void) [ld]
  elf32_hppa_size_stubs [bfd]
    get_local_syms [bfd]
      if we need an export stub
        if (stub_entry == NULL)
          hppa_add_stub [bfd]

In hppa_add_stub(…) if the stub_sec is empty, then we check to see if the stub_sec in the link_sec is empty, and if both those conditions are met then we use the generic add_stub_section(…) to create and place a stub in htab->stub_group[link_sec->id].stub_sec. If there is a stub section in the link_sec already then it is used as the section stub section e.g. htab->stub_group[section->id].stub_sec = stub_sec.

Here is how the ld code calls into the hppa-specific code for the 32-bit target. Line numbers are from binutils-2.15:

main()
  -> [ldmain.c:466] lang_process()
     -> [ldlang.c:4160] lang_for_each_statement_worker()
        -> [ldlang.c:289] ldlang_open_output()
           -> [ldlang.c:1779] open_output()
              -> [ldlang.c:1764] elf32_hppa_link_hash_table_create()
     -> [ldlang.c:4172] open_input_bfds()
        -> [ldlang.c:1888] load_symbols()
           -> [ldlang.c:1475] elf_link_add_object_symbols()
              -> [elflink.c:2995] _bfd_elf_link_create_dynamic_sections()
                 -> [elflink.c:237] elf32_hppa_create_dynamic_sections()
              -> [elflink.c:4055] elf32_hppa_check_relocs()
     -> [ldlang.c:4233] ldemul_before_allocation()
        -> [ldemul.c:77] gldhppa_linux_before_allocation()
           -> [ehppalinux.c:1073] bfd_elf_size_dynamic_sections()
              -> [elflink.c:4981] elf32_hppa_size_dynamic_sections
     -> [ldlang.c:4311] ldemul_finish()
        -> [ldemul.c:90] gldhppalinux_finish()
           -> [ehppalinux.c:295] elf32_hppa_setup_section_lists()
           -> [ehppalinux.c:305] lang_for_each_statement_worker()
              -> [ldlang.c:294] elf32_hppa_next_input_section()
           -> [ehppalinux.c:328] elf32_hppa_set_gp()
           -> [ehppalinux.c:337] elf32_hppa_build_stubs()
  -> [ldmain.c:475] ldwrite()
     -> [ldwrite.c:565] elf32_hppa_final_link()
        -> [elf32-hppa.c:3195] bfd_elf_final_link()
           -> [elflink.c:7579] elf_link_input_bfd()
              -> [elflink.c:6652] elf32_hppa_relocate_section()
           -> [elflink.c:7702] bfd_hash_traverse()
              -> [hash.c:492] elf_link_output_extsym()
                 -> [elflink.c:6124] elf32_hppa_finish_dynamic_symbol()
           -> [elflink.c:7960] elf32_hppa_finish_dynamic_sections()
           -> [elflink.c:7334] _bfd_elf_compute_section_file_positions()
              -> [elf.c:3068] elf32_hppa_post_process_headers()

Disassembler (objdump)

Objdump is (in part) a disassembler. Interesting files:

  • opcodes/hppa-dis.c

  • opcodes/libhppa.h

  • include/opcode/hppa.h: Shared with gas