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.
This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.
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.
Copyright (C) 2012-2017 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.
dda8d76d0d