[Commit]: Add debuglink support to objdump and readelf

[Nick Clifton]

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/ChangeLog
2017-11-15 Nick Clifton <***@redhat.com>

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/ChangeLog
2017-11-15 Nick Clifton <***@redhat.com>

PR 15152
* 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/ChangeLog
2017-11-15 Nick Clifton <***@redhat.com>

PR 15152
* testsuite/ld-avr/gc-section-debugline.d: Update expected
output.

[Joseph Myers]

This patch causes problems for glibc linknamespace tests because of how it
changes the output format of readelf on .a files.

Previously, "readelf -W -s libc.a" would produce output starting e.g.:

File: /scratch/jmyers/glibc/many8/build/glibcs/x86_64-linux-gnu/glibc/libc.a(init-first.o)

Symbol table '.symtab' contains 30 entries:

and continuing with symbol information for each object in that .a file.
After this commit, instead it starts:

File: /scratch/jmyers/glibc/many8/build/glibcs/x86_64-linux-gnu/glibc/libc.a

Symbol table '.symtab' contains 30 entries:

and every object's symbol information starts with the same File: line,
missing any information about which object's symbols (within libc.a) are
being listed.

I think the previous File: lines that said libc.a(init-first.o) etc.,
identifying the particular object within libc.a, were clearly preferable,
and the glibc linknamespace tests rely on having that information about
the individual object within libc.a.

[Nick Clifton]

Hi Joseph,

Post by Joseph Myers
This patch causes problems for glibc linknamespace tests because of how it
changes the output format of readelf on .a files.
File: /scratch/jmyers/glibc/many8/build/glibcs/x86_64-linux-gnu/glibc/libc.a(init-first.o)
and continuing with symbol information for each object in that .a file.
File: /scratch/jmyers/glibc/many8/build/glibcs/x86_64-linux-gnu/glibc/libc.a

Oops - sorry about that. It must be a snafu in my update to the file name printing code.
I will investigate and try to get a fix for it today.

Cheers
Nick

[Nick Clifton]

Hi Joseph,

Post by Joseph Myers
This patch causes problems for glibc linknamespace tests because of how it
changes the output format of readelf on .a files.

Sorry about that. This has now been fixed:

[master 6a6196fc71] Fix a snafu in a previous update to readelf that stopped it from printing archive member names along with the archive file name.

Cheers
Nick

[H.J. Lu]

Post by Nick Clifton
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
$ readelf -wi main.exe
[...]
<15> DW_AT_comp_dir : (alt indirect string, offset: 0x30c)
[...]
$ readelf -wiK main.exe
main.exe: Found separate debug info file: dwz.debug
[...]
<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
$ readelf -wiK main.exe
main.exe: Found separate debug info file: dwz.debug
[...]
[...]
The patch also adds the ability to display the contents of debuglink
$ readelf -wk main.exe
Separate debug info file: dwz.debug
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,
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/ChangeLog
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
(current_file_size, string_table, string_table_length, elf_header)
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.

I am checking this to fix the build with GCC 4.2:

cc1: warnings being treated as errors
binutils-gdb/binutils/dwarf.c: In function \u2018load_separate_debug_info\u2019:
binutils-gdb/binutils/dwarf.c:9650: warning: declaration of
\u2018link\u2019 shadows a global declaration
/usr/include/unistd.h:757: warning: shadowed declaration is here

* dwarf.c (load_separate_debug_info): Rename argument name from
link to xlink.
---
binutils/ChangeLog | 5 +++++
binutils/dwarf.c | 6 +++---
2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/binutils/ChangeLog b/binutils/ChangeLog
index eab683047e..75ef5cd032 100644
--- a/binutils/ChangeLog
+++ b/binutils/ChangeLog
@@ -1,3 +1,8 @@
[phone] H.J. Lu <***@intel.com>
+
+ * dwarf.c (load_separate_debug_info): Rename argument name from
+ link to xlink.
+
2017-11-24 H.J. Lu <***@intel.com>

PR binutils/22444
diff --git a/binutils/dwarf.c b/binutils/dwarf.c
index 8b968797af..a92e7b1fc6 100644
--- a/binutils/dwarf.c
+++ b/binutils/dwarf.c
@@ -9647,7 +9647,7 @@ parse_gnu_debugaltlink (struct dwarf_section *
section, void * data)

static void *
load_separate_debug_info (const char * main_filename,
- struct dwarf_section * link,
+ struct dwarf_section * xlink,
parse_func_type parse_func,
check_func_type check_func,
void * func_data)
@@ -9658,10 +9658,10 @@ load_separate_debug_info (const char *
main_filename,
size_t canon_dirlen;
size_t dirlen;

- if ((separate_filename = parse_func (link, func_data)) == NULL)
+ if ((separate_filename = parse_func (xlink, func_data)) == NULL)
{
warn (_("Corrupt debuglink section: %s\n"),
- link->name ? link->name : link->uncompressed_name);
+ xlink->name ? xlink->name : xlink->uncompressed_name);
return FALSE;
}