Re: Problems while debugging fortran

Re: Problems while debugging fortran

[François-Xavier Coudert]

Hi,

> This is very unclear, since they don't explain what "support"
> refers to. But for people stuck with XLF, if we can improve their
> lives without hurting the rest of GDB, I'm ok with compromising and
> using this attribute value be used to find the main.

I'd like to support this comprise, and I'll note that other compilers
(Intel and Sun, at least) already use this convention.

For the longer term, what do you think is the optimal solution? I'd
like to make gfortran, the Fortran front-end in GCC, do The Right
Thing, but what is it? Should we add this DW_AT_calling_convention tag
for the time being, until the meaning of the DWARF standard is made
clearer?

FX

PS: I might submit patches to GDB in the future. Could someone send me
copyright assignment form? (I already have a GCC assignment, if that
makes any difference)

Re: Problems while debugging fortran

[Daniel Jacobowitz]

On Thu, Oct 25, 2007 at 05:06:54PM +0100, Fran?ois-Xavier Coudert wrote:
> For the longer term, what do you think is the optimal solution? I'd
> like to make gfortran, the Fortran front-end in GCC, do The Right
> Thing, but what is it? Should we add this DW_AT_calling_convention tag
> for the time being, until the meaning of the DWARF standard is made
> clearer?

I'll let Jim answer this, though I think it's reasonable.

> PS: I might submit patches to GDB in the future. Could someone send me
> copyright assignment form? (I already have a GCC assignment, if that
> makes any difference)

Sure, I will.

-- 
Daniel Jacobowitz
CodeSourcery

Re: Problems while debugging fortran

[Jim Blandy]

Daniel Jacobowitz <drow at false.org> writes:
> On Thu, Oct 25, 2007 at 05:06:54PM +0100, Fran?ois-Xavier Coudert wrote:
>> For the longer term, what do you think is the optimal solution? I'd
>> like to make gfortran, the Fortran front-end in GCC, do The Right
>> Thing, but what is it? Should we add this DW_AT_calling_convention tag
>> for the time being, until the meaning of the DWARF standard is made
>> clearer?
>
> I'll let Jim answer this, though I think it's reasonable.

To be clear: I think the actual code in Carlos's patch is just fine.
The comment, though, should not say things that are simply untrue.
Which is why I suggested a new comment, instead of rejecting the
patch.  Whether or not we like the state of DWARF in this regard, the
comment should correct describes the state of play, no?

Re: Problems while debugging fortran

[Daniel Jacobowitz]

On Thu, Oct 25, 2007 at 11:43:57AM -0700, Jim Blandy wrote:
> To be clear: I think the actual code in Carlos's patch is just fine.
> The comment, though, should not say things that are simply untrue.
> Which is why I suggested a new comment, instead of rejecting the
> patch.  Whether or not we like the state of DWARF in this regard, the
> comment should correct describes the state of play, no?

  However, the Fortran main program receives its arguments via a
  special calling convention

I don't think that's true.  As far as I know it has a perfectly
ordinary calling convention.

As for Carlos's comment, I don't know if it's true or not, but
it certainly seems to be what everyone else interprets the
DWARF standard to suggest :-)

-- 
Daniel Jacobowitz
CodeSourcery

Re: Problems while debugging fortran

[Jim Blandy]

Here's a revised comment that may explain what's going on better:

  /* DWARF doesn't provide a way to identify a program's source-level
     entry point.  DW_AT_calling_convention attributes are only meant
     to describe functions' calling conventions.

     However, because it's a necessary piece of information in
     Fortran, and because DW_CC_program is the only piece of debugging
     information whose definition refers to a 'main program' at all,
     several compilers have begun marking Fortran main programs with
     DW_CC_program --- even when those functions use the standard
     calling conventions.

     So until DWARF specifies a way to provide this information and
     compilers pick up the new representation, we'll support this
     practice.  */

Re: Problems while debugging fortran

[Joel Brobecker]

> Here's a revised comment that may explain what's going on better:
> 
>   /* DWARF doesn't provide a way to identify a program's source-level
>      entry point.  DW_AT_calling_convention attributes are only meant
>      to describe functions' calling conventions.
> 
>      However, because it's a necessary piece of information in
>      Fortran, and because DW_CC_program is the only piece of debugging
>      information whose definition refers to a 'main program' at all,
>      several compilers have begun marking Fortran main programs with
>      DW_CC_program --- even when those functions use the standard
>      calling conventions.
> 
>      So until DWARF specifies a way to provide this information and
>      compilers pick up the new representation, we'll support this
>      practice.  */

I think that's a great comment. Let's use that one.

-- 
Joel

Re: Problems while debugging fortran

[Carlos Eduardo Seo]

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Joel Brobecker wrote:
> I think that's a great comment. Let's use that one.
> 

All right. Here's the updated patch with Jim's comments. Ok now?

Regards,

- --
Carlos Eduardo Seo
Software Engineer
IBM Linux Technology Center
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[-- Attachment #2: fortran-main.diff --]
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2007-10-25  Wu Zhou  <woodzltc@cn.ibm.com>
	    Carlos Eduardo Seo  <cseo@linux.vnet.ibm.com>
	    Jim Blandy  <jimb@codesourcery.com>

	* dwarf2read.c (read_partial_die): check the value
	of DW_AT_calling_convention in Fortran programs.

Index: src/gdb/dwarf2read.c
===================================================================
--- src.orig/gdb/dwarf2read.c
+++ src/gdb/dwarf2read.c
@@ -5616,6 +5616,24 @@ read_partial_die (struct partial_die_inf
         case DW_AT_byte_size:
           part_die->has_byte_size = 1;
           break;
+	case DW_AT_calling_convention:
+	  /* DWARF doesn't provide a way to identify a program's source-level
+	     entry point.  DW_AT_calling_convention attributes are only meant
+	     to describe functions' calling conventions.
+
+	     However, because it's a necessary piece of information in
+	     Fortran, and because DW_CC_program is the only piece of debugging
+	     information whose definition refers to a 'main program' at all,
+	     several compilers have begun marking Fortran main programs with
+	     DW_CC_program --- even when those functions use the standard
+	     calling conventions.
+
+	     So until DWARF specifies a way to provide this information and
+	     compilers pick up the new representation, we'll support this
+	     practice.  */
+	  if ((DW_UNSND (&attr) == DW_CC_program) && (cu->language == language_fortran))
+	    set_main_name (part_die->name);
+	  break;
 	default:
 	  break;
 	}

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Re: Problems while debugging fortran

[Joel Brobecker]

> 2007-10-25  Wu Zhou  <woodzltc@cn.ibm.com>
> 	    Carlos Eduardo Seo  <cseo@linux.vnet.ibm.com>
> 	    Jim Blandy  <jimb@codesourcery.com>
> 
> 	* dwarf2read.c (read_partial_die): check the value
> 	of DW_AT_calling_convention in Fortran programs.

Just one minor comment:

> +	  if ((DW_UNSND (&attr) == DW_CC_program) && (cu->language == language_fortran))

Could you remove the unnecessary extra parens and split this line
into two (it's too long):

        if (DW_UNSND (&attr) == DW_CC_program
            && cu->language == language_fortran)

Your patch is approved with that adjustment.

Thanks,
-- 
Joel

Re: Problems while debugging fortran -- DWARF

[Michael Eager]

Hi --

I haven't been following this thread and was just told about it.
Disclaimer:  I haven't read all of the discussion about this issue.

The DWARF Committee has been considering a couple different
proposals for an extension to DWARF to identify the "main" routine
for Fortran or other languages which need this.  An early version of
the proposal can be found on the DWARF website:
http://dwarfstd.org/Issues.php.  A revised proposal which will
have an attribute in the Compilation Unit DIE which points to the
"main" subprogram is under development.

Carlos Eduardo Seo wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> 
> 
> Joel Brobecker wrote:
>> Just one minor comment:
>>
>>> +      if ((DW_UNSND (&attr) == DW_CC_program) && (cu->language ==
> language_fortran))
>> Could you remove the unnecessary extra parens and split this line
>> into two (it's too long):
>>
>>         if (DW_UNSND (&attr) == DW_CC_program
>>             && cu->language == language_fortran)
>>
>> Your patch is approved with that adjustment.
>>
>> Thanks,
> Ok, here's the version I commited, with Joel's suggestion and approval.
> 
> Regards,
> 
> - --
> Carlos Eduardo Seo
> Software Engineer
> IBM Linux Technology Center
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> 
> 
> ------------------------------------------------------------------------
> 
> 2007-10-25  Wu Zhou  <woodzltc@cn.ibm.com>
> 	    Carlos Eduardo Seo  <cseo@linux.vnet.ibm.com>
> 	    Jim Blandy  <jimb@codesourcery.com>
> 
> 	* dwarf2read.c (read_partial_die): check the value
> 	of DW_AT_calling_convention in Fortran programs.
> 
> Index: src/gdb/dwarf2read.c
> ===================================================================
> --- src.orig/gdb/dwarf2read.c
> +++ src/gdb/dwarf2read.c
> @@ -5616,6 +5616,25 @@ read_partial_die (struct partial_die_inf
>          case DW_AT_byte_size:
>            part_die->has_byte_size = 1;
>            break;
> +	case DW_AT_calling_convention:
> +	  /* DWARF doesn't provide a way to identify a program's source-level
> +	     entry point.  DW_AT_calling_convention attributes are only meant
> +	     to describe functions' calling conventions.
> +
> +	     However, because it's a necessary piece of information in
> +	     Fortran, and because DW_CC_program is the only piece of debugging
> +	     information whose definition refers to a 'main program' at all,
> +	     several compilers have begun marking Fortran main programs with
> +	     DW_CC_program --- even when those functions use the standard
> +	     calling conventions.
> +
> +	     So until DWARF specifies a way to provide this information and
> +	     compilers pick up the new representation, we'll support this
> +	     practice.  */
> +	  if (DW_UNSND (&attr) == DW_CC_program
> +	      && cu->language == language_fortran)
> +	    set_main_name (part_die->name);
> +	  break;
>  	default:
>  	  break;
>  	}


-- 
Michael Eager	 eager@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306  650-325-8077

Re: Problems while debugging fortran

[Andreas Schwab]

Carlos Eduardo Seo <cseo@linux.vnet.ibm.com> writes:

> +	  if ((DW_UNSND (&attr) == DW_CC_program) && (cu->language == language_fortran))

Please remove the extra parens and fold the line to keep it below 80
columns.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."