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Re: Question: using objdump for disassembly and inserting source code with object compiled with -gsplit-dwarf

Sorry for top posting.

The need for specifying a list of directories is for the final linked program.

In my case, if I recall correctly, I checked dis-assemble operation by objdump in the directory where the object is created (both .o and .dwo) and so presumably objdump should be capable of finding the .dwo file from the information in .o file. (The make/build process is very convoluted and so I have to investigate where the compilation takes place exactly.)

I will try to create a sample where gdb can list the source list, but
objdump can't mix the source line information in its disassembly.
(May take time since a very small sample source definitely works with objdump. Maybe a bug of g++ may have crept in somewhere. Let me investigate.)

Again, thank you for your attention on this matter.


ISHIKAWA,chiaki wrote:
Dear Nick,

Sorry for my tardy response.
The mail got buried in other mails and I was tied up with my day job :-(

Nick Clifton wrote:
Hi chiaki,

However, for a medium size c++ file, I found that the source
inclusion is not very good. The function signature is inserted, but
no source code lines somehow.
Is this to be expected?


I see. Then I think I am seeing a bug.

Or is there a known bug with objdump?

It is a bug, but not a known one.  Please could you open a bugzilla
for the problem, along with, if possible, a small(ish) test case that
reproduces the problem.

I will try, but not sure if I will succeed in a reasonable amount of time.

It is possible that gcc 5.3 or 6.1 may not be producing correct DWARF
in .o and .dwp which objdump can grok

This is entirely possible.  But if so, then it still may be possible to
have objdump warn the user that the debug info is

Right. binutils programs ought to warn the user if they encounter
unexpected data format.

As an aside - is GDB able to produce correct source+disassembly listings
from the same input file(s) ?  If so then this would point more towards
objdump being at fault.  If not then it may well be a G++ problem.

GDB definitely can print the source line, etc.

However, there is a catch. And I am afraid that it could be the cause of
the problem.

GDB has a feature that lets us tell where gdb should try to find the
.dwo file (the external auxiliary debug information file aside from the
.o file itself).
Specifically, "set debug-file-directory" command is used to list the
directories where gdb ought to look for the related .dwo files.

The said medium-sized program is linked from object files from various
directories and thus we need to tell GDB the directories where to look
for the .dwo files.

E.g.: from my .gdbinit file:
# Path for looking for .dwo files.
source /NREF-COMM-CENTRAL/work-dir/d.dirs
/NREF-COMM-CENTRAL/work-dir/d.dirs contains the following line:
set debug-file-directory

Now, I am not sure. Come to think of it, the source file and line number
is very likely to be in .o file and .dwo file contains additional data
type information, etc.
(Aha, now I see. the source file information in .o file is
only relative to the compilation directory, i.e. where the compilation
takes place, and thus GDB needs to know the full pathname from the side
channel?: that is what set debug-file-directory does (?).)

If my guess is correct, then
this suggests that objdump (and friends) may need to take an optional
argument something like
-G list-of-directories-separated-by-colon
to tell it where to look for .dwo files.

Anyway, I will try to see if I can create a smallish file to re-create
the problem.




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