Re: [PATCH] Add extensions to dwarf2.def

[Pierre-Marie de Rodat <derodat@adacore.com>]

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Cary,

Thank you for your answer!

On 08/13/2015 09:01 PM, Cary Coutant wrote:
> I don't think you really need a new TAG here -- DW_TAG_constant could
> just as easily take DW_AT_GNU_numerator and DW_AT_GNU_denominator as
> an alternative to DW_AT_const_value.

Good idea! I updated the patch accordingly.

> I'm not really sure why DW_AT_small was defined to refer to a
> DW_TAG_constant DIE rather than just providing the constant as the
> attribute value. It would seem more efficient, space-wise, to have a
> DW_AT_scale attribute that would provide a multiplicative scale
> factor, and an optional DW_AT_scale_divisor to provide the denominator
> if necessary.

Agreed.

> Another, perhaps far-fetched, alternative would be to introduce a new
> form that would represent a rational constant as two unsigned LEB128
> values, and allow that form for DW_AT_const_value and/or for
> DW_AT_small.

Indeed, that's an option, but I find it not very convenient: a new form 
would require us to enhance all DWARF reading tools whereas adding new 
tags and attributes is very smooth (not sure this is a good reason, but 
anyway...).

> For now, I'd suggest going with your proposal, except use the existing
> DW_TAG_constant instead of a new TAG. (I.e., just add the two new
> DW_AT_numerator and DW_AT_denominator attributes.)

That's what I did.

>> include/
>>          * dwarf2.def (DW_AT_GNU_bias): New attribute.
>
> This is OK. Looks like a good idea to me.

Great. Thank you again! I comitted the two attached (and updated) 
patches. I will update the corresponding dwarf2out.c changes I submitted 
on July as well.

I also tried to create the new pages on the wiki but it says "You are 
not allowed to edit this page." 
(<https://gcc.gnu.org/wiki/DW_AT_GNU_numerator_denominator?action=edit>, 
I'm logged in as pmderodat). Does anyone know how I should proceed?

-- 
Pierre-Marie de Rodat

[-- Attachment #2: 0001-DWARF2-add-extensions-to-handle-fixed-point-types.patch --]
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From 5b18866caaa8206788baf086c02a7aaf91d555a6 Mon Sep 17 00:00:00 2001
From: Pierre-Marie de Rodat <derodat@adacore.com>
Date: Tue, 9 Jun 2015 10:31:50 +0200
Subject: [PATCH 1/2] DWARF2: add extensions to handle fixed point types

include/ChangeLog:

	* dwarf2.def (DW_AT_GNU_numerator, DW_AT_GNU_denominator): New
	attributes.
---
 include/ChangeLog  | 5 +++++
 include/dwarf2.def | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/include/ChangeLog b/include/ChangeLog
index 46a4a28..ee59133 100644
--- a/include/ChangeLog
+++ b/include/ChangeLog
@@ -1,3 +1,8 @@
+2015-08-14  Pierre-Marie de Rodat  <derodat@adacore.com>
+
+	* dwarf2.def (DW_AT_GNU_numerator, DW_AT_GNU_denominator): New
+	attributes.
+
 2015-08-11  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>
 
 	* ansidecl.h (GCC_FINAL): New macro.
diff --git a/include/dwarf2.def b/include/dwarf2.def
index e61cfbe..9603c04 100644
--- a/include/dwarf2.def
+++ b/include/dwarf2.def
@@ -404,6 +404,10 @@ DW_AT (DW_AT_VMS_rtnbeg_pd_address, 0x2201)
    See http://gcc.gnu.org/wiki/DW_AT_GNAT_descriptive_type .  */
 DW_AT (DW_AT_use_GNAT_descriptive_type, 0x2301)
 DW_AT (DW_AT_GNAT_descriptive_type, 0x2302)
+/* Rational constant extension.
+   See https://gcc.gnu.org/wiki/DW_AT_GNU_numerator_denominator .  */
+DW_TAG (DW_AT_GNU_numerator, 0x2303)
+DW_TAG (DW_AT_GNU_denominator, 0x2304)
 /* UPC extension.  */
 DW_AT (DW_AT_upc_threads_scaled, 0x3210)
 /* PGI (STMicroelectronics) extensions.  */
-- 
2.4.6


[-- Attachment #3: 0002-DWARF2-add-extensions-to-handle-biased-types.patch --]
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From fcddb9fe71187eca4f49576c4f36e5a3d051b669 Mon Sep 17 00:00:00 2001
From: Pierre-Marie de Rodat <derodat@adacore.com>
Date: Tue, 9 Jun 2015 10:31:50 +0200
Subject: [PATCH 2/2] DWARF2: add extensions to handle biased types

include/ChangeLog:

	* dwarf2.def (DW_AT_GNU_bias): New attribute.
---
 include/ChangeLog  | 4 ++++
 include/dwarf2.def | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/include/ChangeLog b/include/ChangeLog
index ee59133..6962f85 100644
--- a/include/ChangeLog
+++ b/include/ChangeLog
@@ -1,5 +1,9 @@
 2015-08-14  Pierre-Marie de Rodat  <derodat@adacore.com>
 
+	* dwarf2.def (DW_AT_GNU_bias): New attribute.
+
+2015-08-14  Pierre-Marie de Rodat  <derodat@adacore.com>
+
 	* dwarf2.def (DW_AT_GNU_numerator, DW_AT_GNU_denominator): New
 	attributes.
 
diff --git a/include/dwarf2.def b/include/dwarf2.def
index 9603c04..2dfee56 100644
--- a/include/dwarf2.def
+++ b/include/dwarf2.def
@@ -408,6 +408,9 @@ DW_AT (DW_AT_GNAT_descriptive_type, 0x2302)
    See https://gcc.gnu.org/wiki/DW_AT_GNU_numerator_denominator .  */
 DW_TAG (DW_AT_GNU_numerator, 0x2303)
 DW_TAG (DW_AT_GNU_denominator, 0x2304)
+/* Biased integer extension.
+   See https://gcc.gnu.org/wiki/DW_AT_GNU_bias .  */
+DW_TAG (DW_AT_GNU_bias, 0x2305)
 /* UPC extension.  */
 DW_AT (DW_AT_upc_threads_scaled, 0x3210)
 /* PGI (STMicroelectronics) extensions.  */
-- 
2.4.6