GCC 4.6.1 emits discriminators in DWARF2 mode

GCC 4.6.1 emits discriminators in DWARF2 mode

[Anitha Boyapati]

Hi,

I have recently switched to using GCC 4.6.1 (from 4.5.1) for AVR
target which supports only DWARF2 format. Now I notice a change in
.debug_line section format in 4.6.1.  A quick look at the assembly
shows that '.loc' directives are emitted with discriminators.


Firstly, aren't discriminators introduced in DWARF 4? Little more
digging shows that the following fix is missing in 4.6.1 release. It
breaks the current dwarf2 parsers/readers. I think it is worth filing
a bug.

http://gcc.gnu.org/viewcvs/trunk/gcc/dwarf2out.c?r1=171846&r2=171852&diff_format=h

Secondly, in gcc4.5.1, the directive (.loc) is not emitted and still
we are able to map line numbers to address. Please help me understand
how introducing .loc directive affects debug_line format in gcc 4.6.1.

Thanks
--
 Anitha

Re: GCC 4.6.1 emits discriminators in DWARF2 mode

[Paulo J. Matos]

On 20/10/11 15:06, Anitha Boyapati wrote:
>
> Firstly, aren't discriminators introduced in DWARF 4? Little more
> digging shows that the following fix is missing in 4.6.1 release. It
> breaks the current dwarf2 parsers/readers. I think it is worth filing
> a bug.
>

Anitha, if you only want dwarf2 produced, with no extensions you should 
use on the command line -gdwarf-2 -gstrict-dwarf. That should block any 
extensions to dwarf2.

-- 
PMatos

Re: GCC 4.6.1 emits discriminators in DWARF2 mode

[Anitha Boyapati]

On 20 October 2011 20:27, Paulo J. Matos <paulo@matos-sorge.com> wrote:
> On 20/10/11 15:06, Anitha Boyapati wrote:
>>
>> Firstly, aren't discriminators introduced in DWARF 4? Little more
>> digging shows that the following fix is missing in 4.6.1 release. It
>> breaks the current dwarf2 parsers/readers. I think it is worth filing
>> a bug.
>>
>
> Anitha, if you only want dwarf2 produced, with no extensions you should use
> on the command line -gdwarf-2 -gstrict-dwarf. That should block any
> extensions to dwarf2.

I did try that already. Inspite of giving -gstrict-dwarf2, it
generates .loc info with discriminators.
For e.g,

$ avr-gcc  test.c -gstrict-dwarf -S  -mmcu=atxmega128a1 -g -gdwarf-2

.LFB0:
    .file 1 "test.c"
    .loc 1 3 0
    push r28
...
.L5:
    .loc 1 9 0
    std Y+3,__zero_reg__
    std Y+4,__zero_reg__
    rjmp .L3
.L4:
    .loc 1 9 0 is_stmt 0 discriminator 2
    ldd r24,Y+3
 ...


(Note that the gcc version is 4.6.1) A look at gcc-4_6_branch log says
that the fix is not backported when it got fixed in trunk (link given
in previous mail)




-- 
 Anitha

Re: GCC 4.6.1 emits discriminators in DWARF2 mode

[Eric Botcazou]

> Firstly, aren't discriminators introduced in DWARF 4? Little more
> digging shows that the following fix is missing in 4.6.1 release. It
> breaks the current dwarf2 parsers/readers. I think it is worth filing
> a bug.
>
> http://gcc.gnu.org/viewcvs/trunk/gcc/dwarf2out.c?r1=171846&r2=171852&diff_f
>ormat=h

Yes, this is a real nuisance for some DWARF consumers.  You need to ask a RM 
about backporting the fix.

> Secondly, in gcc4.5.1, the directive (.loc) is not emitted and still
> we are able to map line numbers to address. Please help me understand
> how introducing .loc directive affects debug_line format in gcc 4.6.1.

.loc directives are processed by the assembler, which then builds .debug_line.

-- 
Eric Botcazou