[Bug binutils/17940] See unexpected diagnostic from msp430-elf-objdump BFD: Dwarf Error: mangled line number section.

[nickc at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17940

Nick Clifton <nickc at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2015-07-14
     Ever confirmed|0                           |1

--- Comment #9 from Nick Clifton <nickc at redhat dot com> ---
Hi Orlando,

> I compiled the msp430-elf toolchain and I seem to have encountered this
> error even after applying the aforementioned patch.

The problem I believe is in the linker script that you are using.  This script
is not combining the partial .debug_line sections into a single, correct,
.debug_line section.  Vis:

  % readelf -S blink.elf
...
  [13] .debug_line       PROGBITS        00000000 0007a8 000118 00      0   0 
1
  [14] .debug_line.crt_0 PROGBITS        00000000 0008c0 000014 00   W  0   0 
1
  [15] .debug_line.crt_0 PROGBITS        00000000 0008d4 00007b 00   W  0   0 
1
  [16] .debug_line.fini  PROGBITS        00000000 00094f 00001d 00   W  0   0 
1
  [17] .debug_ranges     PROGBITS        00000000 00096c 000024 00      0   0 
4
  [18] .debug_line.crt_0 PROGBITS        00000000 000990 00001b 00   W  0   0 
1
  [19] .debug_line.crt_0 PROGBITS        00000000 0009ab 00000f 00   W  0   0 
1
  [20] .debug_line.init  PROGBITS        00000000 0009ba 00001a 00   W  0   0 
1
...

There should only be one .debug_line section in blink.elf.

I assume that you are using an MCU specific linker script.  What you need to do
is to find the line that reads:

  .debug_line     0 : { *(.debug_line) }

(It is probably near the end of the script).  Replace it with this line:

  .debug_line     0 : { *(.debug_line .debug_line.* .debug_line_end ) }

Then rebuild blink.elf.

What is happening is that when the assembler creates an object file it creates
lots of .debug_line.<foo> sections, one for each function in the input source
file.  That way, if the linker garbage collection code decides to remove
function <foo> it can also remove the .debug_line.<foo> section associated with
that function, and so the line debug information remains consistent with the
actual code in the executable.  But in order for this to work you need a linker
script that will combine all of the remaining .debug_line.<foo> sections into a
final, big, correct, .debug_line section.



> What is more, when
> disassembling the binary, I have encountered a few problems with the way
> label names are recorded in the resulting ELF.

> 00002da0  30 30 66 61 36 38 20 3c  4c 30 01 3e 3a 0a 20 20  |00fa68 <L0.>:. 

> [output trimmed, notice the 0x01 after L0]

Actually this is correct.  The .L0^A symbol is an assembler "Local Label". 
Have a look in the assembler documentation for that name to see what is going
on...


Cheers
  Nick

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