RFC: Change of dw2 DWARF_OFFSET_SIZE on 64-bit to POINTER_SIZE

RFC: Change of dw2 DWARF_OFFSET_SIZE on 64-bit to POINTER_SIZE

[Kai Tietz]

Hello,

The default value of DWARF_OFFSET_SIZE of 4 is for w64 a problem, because 
on w64 there are only 64-bit imaged based relocations present and the 
offset is build of this offset is computed by a secrel offset. 
Additionally there is no way for this target to set VA to zero as done for 
elf. I prepared a patch for binutils to change this behaviour. As we 
discussed is the additional memory consume for 64-bit less, so I want to 
query if there is general agreement in changing this value in general for 
64-bit targets?
These should affect DW_AT_stmt_list and the arange to use 8 byte offset 
for 64-bit targets.

The change would be in dwarf2out.c and looks like:
....
 /* The size in bytes of a DWARF field indicating an offset or length
    relative to a debug info section, specified to be 4 bytes in the
    DWARF-2 specification.  The SGI/MIPS ABI defines it to be the same
    as PTR_SIZE.  */

 #ifndef DWARF_OFFSET_SIZE
-#define DWARF_OFFSET_SIZE 4
+#define DWARF_OFFSET_SIZE (TARGET_64BIT ? 8 : 4)
 #endif...

As I discussed with binutils, they would be happy to change this, if gcc 
would change its behaviour, too.
 
Regards,
 Kai Tietz

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Re: RFC: Change of dw2 DWARF_OFFSET_SIZE on 64-bit to POINTER_SIZE

[NightStrike]

On 8/1/08, Kai Tietz <Kai.Tietz@onevision.com> wrote:
> Hello,
>
> The default value of DWARF_OFFSET_SIZE of 4 is for w64 a problem, because
> on w64 there are only 64-bit imaged based relocations present and the
> offset is build of this offset is computed by a secrel offset.
> Additionally there is no way for this target to set VA to zero as done for
> elf. I prepared a patch for binutils to change this behaviour. As we
> discussed is the additional memory consume for 64-bit less, so I want to
> query if there is general agreement in changing this value in general for
> 64-bit targets?
> These should affect DW_AT_stmt_list and the arange to use 8 byte offset
> for 64-bit targets.
>
> The change would be in dwarf2out.c and looks like:
> ....
>  /* The size in bytes of a DWARF field indicating an offset or length
>    relative to a debug info section, specified to be 4 bytes in the
>    DWARF-2 specification.  The SGI/MIPS ABI defines it to be the same
>    as PTR_SIZE.  */
>
>  #ifndef DWARF_OFFSET_SIZE
> -#define DWARF_OFFSET_SIZE 4
> +#define DWARF_OFFSET_SIZE (TARGET_64BIT ? 8 : 4)
>  #endif...
>
> As I discussed with binutils, they would be happy to change this, if gcc
> would change its behaviour, too.

I haven't seen a response on this yet.  Have I missed it?

Re: RFC: Change of dw2 DWARF_OFFSET_SIZE on 64-bit to POINTER_SIZE

[NightStrike]

On 8/1/08, Kai Tietz <Kai.Tietz@onevision.com> wrote:
> Hello,
>
> The default value of DWARF_OFFSET_SIZE of 4 is for w64 a problem, because
> on w64 there are only 64-bit imaged based relocations present and the
> offset is build of this offset is computed by a secrel offset.
> Additionally there is no way for this target to set VA to zero as done for
> elf. I prepared a patch for binutils to change this behaviour. As we
> discussed is the additional memory consume for 64-bit less, so I want to
> query if there is general agreement in changing this value in general for
> 64-bit targets?
> These should affect DW_AT_stmt_list and the arange to use 8 byte offset
> for 64-bit targets.
>
> The change would be in dwarf2out.c and looks like:
> ....
>  /* The size in bytes of a DWARF field indicating an offset or length
>    relative to a debug info section, specified to be 4 bytes in the
>    DWARF-2 specification.  The SGI/MIPS ABI defines it to be the same
>    as PTR_SIZE.  */
>
>  #ifndef DWARF_OFFSET_SIZE
> -#define DWARF_OFFSET_SIZE 4
> +#define DWARF_OFFSET_SIZE (TARGET_64BIT ? 8 : 4)
>  #endif...
>
> As I discussed with binutils, they would be happy to change this, if gcc
> would change its behaviour, too.

I haven't seen a response on this yet.  Have I missed it?

Re: RFC: Change of dw2 DWARF_OFFSET_SIZE on 64-bit to POINTER_SIZE

[NightStrike]

On 8/1/08, Kai Tietz <Kai.Tietz@onevision.com> wrote:
> Hello,
>
> The default value of DWARF_OFFSET_SIZE of 4 is for w64 a problem, because
> on w64 there are only 64-bit imaged based relocations present and the
> offset is build of this offset is computed by a secrel offset.
> Additionally there is no way for this target to set VA to zero as done for
> elf. I prepared a patch for binutils to change this behaviour. As we
> discussed is the additional memory consume for 64-bit less, so I want to
> query if there is general agreement in changing this value in general for
> 64-bit targets?
> These should affect DW_AT_stmt_list and the arange to use 8 byte offset
> for 64-bit targets.
>
> The change would be in dwarf2out.c and looks like:
> ....
>  /* The size in bytes of a DWARF field indicating an offset or length
>    relative to a debug info section, specified to be 4 bytes in the
>    DWARF-2 specification.  The SGI/MIPS ABI defines it to be the same
>    as PTR_SIZE.  */
>
>  #ifndef DWARF_OFFSET_SIZE
> -#define DWARF_OFFSET_SIZE 4
> +#define DWARF_OFFSET_SIZE (TARGET_64BIT ? 8 : 4)
>  #endif...
>
> As I discussed with binutils, they would be happy to change this, if gcc
> would change its behaviour, too.

I haven't seen a response on this yet.  Have I missed it?

Re: RFC: Change of dw2 DWARF_OFFSET_SIZE on 64-bit to POINTER_SIZE

[NightStrike]

On 8/1/08, Kai Tietz <Kai.Tietz@onevision.com> wrote:
> Hello,
>
> The default value of DWARF_OFFSET_SIZE of 4 is for w64 a problem, because
> on w64 there are only 64-bit imaged based relocations present and the
> offset is build of this offset is computed by a secrel offset.
> Additionally there is no way for this target to set VA to zero as done for
> elf. I prepared a patch for binutils to change this behaviour. As we
> discussed is the additional memory consume for 64-bit less, so I want to
> query if there is general agreement in changing this value in general for
> 64-bit targets?
> These should affect DW_AT_stmt_list and the arange to use 8 byte offset
> for 64-bit targets.
>
> The change would be in dwarf2out.c and looks like:
> ....
>  /* The size in bytes of a DWARF field indicating an offset or length
>    relative to a debug info section, specified to be 4 bytes in the
>    DWARF-2 specification.  The SGI/MIPS ABI defines it to be the same
>    as PTR_SIZE.  */
>
>  #ifndef DWARF_OFFSET_SIZE
> -#define DWARF_OFFSET_SIZE 4
> +#define DWARF_OFFSET_SIZE (TARGET_64BIT ? 8 : 4)
>  #endif...
>
> As I discussed with binutils, they would be happy to change this, if gcc
> would change its behaviour, too.

I haven't seen a response on this yet.  Have I missed it?

Re: RFC: Change of dw2 DWARF_OFFSET_SIZE on 64-bit to POINTER_SIZE

[Jakub Jelinek]

On Tue, Aug 26, 2008 at 01:51:19PM -0400, NightStrike wrote:
> On 8/1/08, Kai Tietz <Kai.Tietz@onevision.com> wrote:
> > Hello,
> >
> > The default value of DWARF_OFFSET_SIZE of 4 is for w64 a problem, because
> > on w64 there are only 64-bit imaged based relocations present and the
> > offset is build of this offset is computed by a secrel offset.
> > Additionally there is no way for this target to set VA to zero as done for
> > elf. I prepared a patch for binutils to change this behaviour. As we
> > discussed is the additional memory consume for 64-bit less, so I want to
> > query if there is general agreement in changing this value in general for
> > 64-bit targets?
> > These should affect DW_AT_stmt_list and the arange to use 8 byte offset
> > for 64-bit targets.
> >
> > The change would be in dwarf2out.c and looks like:
> > ....
> >  /* The size in bytes of a DWARF field indicating an offset or length
> >    relative to a debug info section, specified to be 4 bytes in the
> >    DWARF-2 specification.  The SGI/MIPS ABI defines it to be the same
> >    as PTR_SIZE.  */
> >
> >  #ifndef DWARF_OFFSET_SIZE
> > -#define DWARF_OFFSET_SIZE 4
> > +#define DWARF_OFFSET_SIZE (TARGET_64BIT ? 8 : 4)
> >  #endif...
> >
> > As I discussed with binutils, they would be happy to change this, if gcc
> > would change its behaviour, too.
> 
> I haven't seen a response on this yet.  Have I missed it?

All the world isn't W64, and just because one 64-bit target isn't able to
use it doesn't mean we want to punish all 64-bit targets by enlarging the
debug info.  So, please do it for W64 only if you have to.

	Jakub

Re: RFC: Change of dw2 DWARF_OFFSET_SIZE on 64-bit to POINTER_SIZE

[NightStrike]

On 8/1/08, Kai Tietz <Kai.Tietz@onevision.com> wrote:
> Hello,
>
> The default value of DWARF_OFFSET_SIZE of 4 is for w64 a problem, because
> on w64 there are only 64-bit imaged based relocations present and the
> offset is build of this offset is computed by a secrel offset.
> Additionally there is no way for this target to set VA to zero as done for
> elf. I prepared a patch for binutils to change this behaviour. As we
> discussed is the additional memory consume for 64-bit less, so I want to
> query if there is general agreement in changing this value in general for
> 64-bit targets?
> These should affect DW_AT_stmt_list and the arange to use 8 byte offset
> for 64-bit targets.
>
> The change would be in dwarf2out.c and looks like:
> ....
>  /* The size in bytes of a DWARF field indicating an offset or length
>    relative to a debug info section, specified to be 4 bytes in the
>    DWARF-2 specification.  The SGI/MIPS ABI defines it to be the same
>    as PTR_SIZE.  */
>
>  #ifndef DWARF_OFFSET_SIZE
> -#define DWARF_OFFSET_SIZE 4
> +#define DWARF_OFFSET_SIZE (TARGET_64BIT ? 8 : 4)
>  #endif...
>
> As I discussed with binutils, they would be happy to change this, if gcc
> would change its behaviour, too.

I haven't seen a response on this yet.  Have I missed it?

Re: RFC: Change of dw2 DWARF_OFFSET_SIZE on 64-bit to POINTER_SIZE

[Joseph S. Myers]

On Tue, 26 Aug 2008, NightStrike wrote:

> On 8/1/08, Kai Tietz <Kai.Tietz@onevision.com> wrote:
> > Hello,
> >
> > The default value of DWARF_OFFSET_SIZE of 4 is for w64 a problem, because
> > on w64 there are only 64-bit imaged based relocations present and the
> > offset is build of this offset is computed by a secrel offset.
> > Additionally there is no way for this target to set VA to zero as done for
> > elf. I prepared a patch for binutils to change this behaviour. As we
> > discussed is the additional memory consume for 64-bit less, so I want to
> > query if there is general agreement in changing this value in general for
> > 64-bit targets?
> > These should affect DW_AT_stmt_list and the arange to use 8 byte offset
> > for 64-bit targets.
> >
> > The change would be in dwarf2out.c and looks like:
> > ....
> >  /* The size in bytes of a DWARF field indicating an offset or length
> >    relative to a debug info section, specified to be 4 bytes in the
> >    DWARF-2 specification.  The SGI/MIPS ABI defines it to be the same
> >    as PTR_SIZE.  */
> >
> >  #ifndef DWARF_OFFSET_SIZE
> > -#define DWARF_OFFSET_SIZE 4
> > +#define DWARF_OFFSET_SIZE (TARGET_64BIT ? 8 : 4)
> >  #endif...
> >
> > As I discussed with binutils, they would be happy to change this, if gcc
> > would change its behaviour, too.
> 
> I haven't seen a response on this yet.  Have I missed it?

Such a patch is obviously wrong; TARGET_64BIT is a target-specific macro 
used in some particular targets and cannot be used in generic code.  In 
general 64-bit offsets are only needed if a single object has more than 
4GB of debug info.  So such a patch is a pessimization for almost all 
normal code.  Please see the text from the DWARF standard I quoted when 
stopping MIPS64 GNU/Linux from using 64-bit offsets 
<http://gcc.gnu.org/ml/gcc-patches/2006-05/msg00142.html>.

-- 
Joseph S. Myers
joseph@codesourcery.com