binutils-gdb/ld
Nick Clifton dda8d76d0d Add support to readelf and objdump for following links to separate debug information files.
Hi Guys,

  I am applying the rather large patch attached to this email to enhance
  the readelf and objdump programs so that they now have the ability to
  follow links to separate debug info files.  (As requested by PR
  15152).  So for example whereas before we had this output:

    $ readelf -wi main.exe

    Contents of the .debug_info section:
    [...]
    <15>   DW_AT_comp_dir    : (alt indirect string, offset: 0x30c)
    [...]

  With the new option enabled we get:

    $ readelf -wiK main.exe

    main.exe: Found separate debug info file: dwz.debug
    Contents of the .debug_info section (loaded from main.exe):
    [...]
    <15>   DW_AT_comp_dir    : (alt indirect string, offset: 0x30c) /home/nickc/Downloads/dwzm
    [...]

  The link following feature also means that we can get two lots of
  output if the same section exists in both the main file and the
  separate debug info file:

    $ readelf -wiK main.exe
    main.exe: Found separate debug info file: dwz.debug
    Contents of the .debug_info section (loaded from main.exe):
    [...]
    Contents of the .debug_info section (loaded from dwz.debug):
    [...]

  The patch also adds the ability to display the contents of debuglink
  sections:

    $ readelf -wk main.exe
    Contents of the .gnu_debugaltlink section:

      Separate debug info file: dwz.debug
      Build-ID (0x14 bytes):
     c4 a8 89 8d 64 cf 70 8a 35 68 21 f2 ed 24 45 3e 18 7a 7a 93

  Naturally there are long versions of these options (=follow-links and
  =links).  The documentation has been updated as well, and since both
  readelf and objdump use the same set of debug display options, I have
  moved the text into a separate file.  There are also a couple of new
  binutils tests to exercise the new behaviour.

  There are a couple of missing features in the current patch however,
  although I do intend to address them in follow up submissions:

  Firstly the code does not check the build-id inside separate debug
  info files when it is searching for a file specified by a
  .gnu_debugaltlink section.  It just assumes that if the file is there,
  then it contains the information being sought.

  Secondly I have not checked the DWARF-5 version of these link
  features, so there will probably be code to add there.

  Thirdly I have only implemented link following for the
  DW_FORM_GNU_strp_alt format.  Other alternate formats (eg
  DW_FORM_GNU_ref_alt) have yet to be implemented.

  Lastly, whilst implementing this feature I found it necessary to move
  some of the global variables used by readelf (eg section_headers) into
  a structure that can be passed around.  I have moved all of the global
  variables that were necessary to get the patch working, but I need to
  complete the operation and move the remaining, file-specific variables
  (eg dynamic_strings).

Cheers
  Nick

binutils	PR 15152
	* dwarf.h (enum dwarf_section_display_enum): Add gnu_debuglink,
	gnu_debugaltlink and separate_debug_str.
	(struct dwarf_section): Add filename field.
	Add prototypes for load_separate_debug_file, close_debug_file and
	open_debug_file.
	* dwarf.c (do_debug_links): New.
	(do_follow_links): New.
	(separate_debug_file, separate_debug_filename): New.
	(fetch_alt_indirect_string): New function.  Retrieves a string
	from the debug string table in the separate debug info file.
	(read_and_display_attr_value): Use it with DW_FORM_GNU_strp_alt.
	(load_debug_section_with_follow): New function.  Like
	load_debug_section, but if the first attempt fails, then tries
	again in the separate debug info file.
	(introduce): New function.
	(process_debug_info): Use load_debug_section_with_follow and
	introduce.
	(load_debug_info): Likewise.
	(display_debug_lines_raw): Likewise.
	(display_debug_lines_decoded): Likewise.
	(display_debug_macinfo): Likewise.
	(display_debug_macro): Likewise.
	(display_debug_abbrev): Likewise.
	(display_debug_loc): Likewise.
	(display_debug_str): Likewise.
	(display_debug_aranges): Likewise.
	(display_debug_addr); Likewise.
	(display_debug_frames): Likewise.
	(display_gdb_index): Likewise.
	(process_cu_tu_index): Likewise.
	(load_cu_tu_indexes): Likewise.
	(display_debug_links): New function.  Displays the contents of a
	.gnu_debuglink or .gnu_debugaltlink section.
	(calc_gnu_debuglink_ctc32):New function.  Calculates a CRC32
	value.
	(check_gnu_debuglink): New function.  Checks the CRC of a
	potential separate debug info file.
	(parse_gnu_debuglink): New function.  Reads a CRC value out of a
	.gnu_debuglink section.
	(check_gnu_debugaltlink): New function.
	(parse_gnu_debugaltlink): New function.  Reads the build-id value
	out of a .gnu_debugaltlink section.
	(load_separate_debug_info): New function.  Finds and loads a
	separate debug info file.
	(load_separate_debug_file): New function. Attempts to find and
	follow a link to a separate debug info file.
	(free_debug_memory): Free the separate debug info file
	information.
	(opts_table): Add "follow-links" and "links".
	(dwarf_select_sections_by_letters): Add "k" and "K".
	(debug_displays): Reformat.  Add .gnu-debuglink and
	.gnu_debugaltlink.
	Add an extra entry for .debug_str in a separate debug info file.
	* doc/binutils.texi: Move description of debug dump features
	common to both readelf and objdump into...
	* objdump.c (usage): Add -Wk and -WK.
	(load_specific_debug_section): Initialise the filename field in
	the dwarf_section structure.
	(close_debug_file): New function.
	(open_debug_file): New function.
	(dump_dwarf): Load and dump the separate debug info sections.
	* readelf.c (struct filedata): New structure.  Contains various
	variables that used to be global:
	(current_file_size, string_table, string_table_length, elf_header)
	(section_headers, program_headers, dump_sects, num_dump_sects):
	Move into filedata structure.
	(cmdline): New global variable.  Contains list of sections to dump
	by number, as specified on the command line.
	Add filedata parameter to most functions.
	(load_debug_section): Load the string table if it has not already
	been retrieved.
	(close_file): New function.
	(close_debug_file): New function.
	(open_file): New function.
	(open_debug_file): New function.
	(process_object): Process sections in any separate debug info files.
	* doc/debug.options.texi: New file.  Add description of =links and
	=follow-links options.
	* NEWS: Mention the new feature.
	* elfcomm.c: Have the byte gte functions take a const pointer.
	* elfcomm.h: Update prototypes.
	* testsuite/binutils-all/dw5.W: Update expected output.
	* testsuite/binutils-all/objdump.WL: Update expected output.
	* testsuite/binutils-all/objdump.exp: Add test of -WK and -Wk.
	* testsuite/binutils-all/readelf.exp: Add test of -wK and -wk.
	* testsuite/binutils-all/readelf.k: New file.
	* testsuite/binutils-all/objdump.Wk: New file.
	* testsuite/binutils-all/objdump.WK2: New file.
	* testsuite/binutils-all/linkdebug.s: New file.
	* testsuite/binutils-all/debuglink.s: New file.

gas	* testsuite/gas/avr/large-debug-line-table.d: Update expected
	output.
	* testsuite/gas/elf/dwarf2-11.d: Likewise.
	* testsuite/gas/elf/dwarf2-12.d: Likewise.
	* testsuite/gas/elf/dwarf2-13.d: Likewise.
	* testsuite/gas/elf/dwarf2-14.d: Likewise.
	* testsuite/gas/elf/dwarf2-15.d: Likewise.
	* testsuite/gas/elf/dwarf2-16.d: Likewise.
	* testsuite/gas/elf/dwarf2-17.d: Likewise.
	* testsuite/gas/elf/dwarf2-18.d: Likewise.
	* testsuite/gas/elf/dwarf2-5.d: Likewise.
	* testsuite/gas/elf/dwarf2-6.d: Likewise.
	* testsuite/gas/elf/dwarf2-7.d: Likewise.

ld	* testsuite/ld-avr/gc-section-debugline.d: Update expected
	output.
2017-11-15 11:34:03 +00:00
..
emulparams ld: Add OTHER_PLT_SECTIONS 2017-11-12 07:25:36 -08:00
emultempl ld: Replace exp_dataseg_none with exp_seg_none 2017-11-13 08:19:10 -08:00
po ld whitespace fixes 2017-10-12 23:30:43 +10:30
scripttempl ld: Add OTHER_PLT_SECTIONS 2017-11-12 07:25:36 -08:00
testsuite Add support to readelf and objdump for following links to separate debug information files. 2017-11-15 11:34:03 +00:00
.gitignore
aclocal.m4
ChangeLog Add support to readelf and objdump for following links to separate debug information files. 2017-11-15 11:34:03 +00:00
ChangeLog-0001
ChangeLog-0203
ChangeLog-2004
ChangeLog-2005
ChangeLog-2006
ChangeLog-2007
ChangeLog-2008
ChangeLog-2009
ChangeLog-2010
ChangeLog-2011
ChangeLog-2012
ChangeLog-2013
ChangeLog-2014
ChangeLog-2015
ChangeLog-2016
ChangeLog-9197
ChangeLog-9899
config.in Add configure flag to enable gnu hash style by default. 2017-08-08 07:25:39 +09:30
configure ld whitespace fixes 2017-10-12 23:30:43 +10:30
configure.ac ld whitespace fixes 2017-10-12 23:30:43 +10:30
configure.host
configure.tgt i386: Don't add elf32_x86_64 to supported emulations 2017-10-23 14:44:04 -07:00
deffile.h
deffilep.y ld whitespace fixes 2017-10-12 23:30:43 +10:30
dep-in.sed
elf-hints-local.h
fdl.texi
gen-doc.texi S/390: Add support for pgste marker 2017-06-23 08:00:46 +02:00
genscrba.sh
genscripts.sh ld whitespace fixes 2017-10-12 23:30:43 +10:30
h8-doc.texi
ld.h ngettext support 2017-11-07 15:52:52 +10:30
ld.texinfo ld: Correct -z ibt documentation 2017-10-25 08:44:54 -07:00
ldbuildid.c
ldbuildid.h
ldcref.c ld internationalization fixes 2017-10-11 15:04:59 +10:30
ldctor.c
ldctor.h
ldemul.c ELF: Call check_relocs after opening all inputs 2017-10-16 03:50:13 -07:00
ldemul.h ELF: Call check_relocs after opening all inputs 2017-10-16 03:50:13 -07:00
ldexp.c ld: Add fold_segment_align/fold_segment_relro_end/fold_segment_end 2017-11-12 17:20:18 -08:00
ldexp.h ld: Update phase_enum/relro_enum and add seg_align_type 2017-11-12 17:17:58 -08:00
ldfile.c Treat a prefix of "$SYSROOT" in the same way as "=" when parsing linker search paths. 2017-05-18 15:07:59 +01:00
ldfile.h
ldgram.y ld whitespace fixes 2017-10-12 23:30:43 +10:30
ldint.texinfo
ldlang.c ld: Add ldlang_check_relro_region/update lang_find_relro_sections_1 2017-11-12 17:26:11 -08:00
ldlang.h LTO rescan archives 2017-09-02 17:39:04 +09:30
ldlex-wrapper.c
ldlex.h ld: Allow section groups to be resolved as part of a relocatable link 2017-06-06 09:53:38 +01:00
ldlex.l ld whitespace fixes 2017-10-12 23:30:43 +10:30
ldmain.c ld internationalization fixes 2017-10-11 15:04:59 +10:30
ldmain.h
ldmisc.c ld einfo positional arg support 2017-11-15 13:35:03 +10:30
ldmisc.h
ldver.c
ldver.h
ldwrite.c
ldwrite.h
lexsup.c ld whitespace fixes 2017-10-12 23:30:43 +10:30
MAINTAINERS
Makefile.am Correct ld/Makefile earmelfb_fuchsia dependencies 2017-10-10 14:44:58 +10:30
Makefile.in Correct ld/Makefile earmelfb_fuchsia dependencies 2017-10-10 14:44:58 +10:30
mri.c
mri.h
NEWS ld whitespace fixes 2017-10-12 23:30:43 +10:30
pe-dll.c ld whitespace fixes 2017-10-12 23:30:43 +10:30
pe-dll.h PR 21274, ld segfaults linking PE DLL 2017-04-11 19:49:13 +09:30
pep-dll.c
pep-dll.h PR 21274, ld segfaults linking PE DLL 2017-04-11 19:49:13 +09:30
plugin.c ld whitespace fixes 2017-10-12 23:30:43 +10:30
plugin.h
README
stamp-h.in
sysdep.h
testplug2.c
testplug3.c
testplug4.c
testplug.c
TODO

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		README for LD

This is the GNU linker.  It is distributed with other "binary
utilities" which should be in ../binutils.  See ../binutils/README for
more general notes, including where to send bug reports.

There are many features of the linker:

* The linker uses a Binary File Descriptor library (../bfd)
  that it uses to read and write object files.  This helps
  insulate the linker itself from the format of object files.

* The linker supports a number of different object file
  formats.  It can even handle multiple formats at once:
  Read two input formats and write a third.

* The linker can be configured for cross-linking.

* The linker supports a control language.

* There is a user manual (ld.texinfo), as well as the
  beginnings of an internals manual (ldint.texinfo).

Installation
============

See ../binutils/README.

If you want to make a cross-linker, you may want to specify
a different search path of -lfoo libraries than the default.
You can do this by setting the LIB_PATH variable in ./Makefile
or using the --with-lib-path configure switch.

To build just the linker, make the target all-ld from the top level
directory (one directory above this one).

Porting to a new target
=======================

See the ldint.texinfo manual.

Reporting bugs etc
===========================

See ../binutils/README.

Known problems
==============

The Solaris linker normally exports all dynamic symbols from an
executable.  The GNU linker does not do this by default.  This is
because the GNU linker tries to present the same interface for all
similar targets (in this case, all native ELF targets).  This does not
matter for normal programs, but it can make a difference for programs
which try to dlopen an executable, such as PERL or Tcl.  You can make
the GNU linker export all dynamic symbols with the -E or
--export-dynamic command line option.

HP/UX 9.01 has a shell bug that causes the linker scripts to be
generated incorrectly.  The symptom of this appears to be "fatal error
- scanner input buffer overflow" error messages.  There are various
workarounds to this:
  * Build and install bash, and build with "make SHELL=bash".
  * Update to a version of HP/UX with a working shell (e.g., 9.05).
  * Replace "(. ${srcdir}/scripttempl/${SCRIPT_NAME}.sc)" in
    genscripts.sh with "sh ${srcdir}..." (no parens) and make sure the
    emulparams script used exports any shell variables it sets.

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