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[Bug tools/24550] eu-readelf does not know about DW_AT_GNU_{bias,numerator,denumerator}


https://sourceware.org/bugzilla/show_bug.cgi?id=24550

Mark Wielaard <mark at klomp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mark at klomp dot org
            Summary|eu-readelf does not know    |eu-readelf does not know
                   |about DW_AT_GNU_bias        |about
                   |                            |DW_AT_GNU_{bias,numerator,d
                   |                            |enumerator}

--- Comment #1 from Mark Wielaard <mark at klomp dot org> ---
We are also missing GNU_AT_GNU_numerator and GNU_AT_GNU_denominator.

In theory all that is needed is add them to dwarf.h.
Since they are simple constant attributes.

diff --git a/libdw/dwarf.h b/libdw/dwarf.h
index dc5973352..71ca2baae 100644
--- a/libdw/dwarf.h
+++ b/libdw/dwarf.h
@@ -351,6 +351,12 @@ enum
     DW_AT_GNU_pubnames = 0x2134,
     DW_AT_GNU_pubtypes = 0x2135,

+    /* https://gcc.gnu.org/wiki/DW_AT_GNU_numerator_denominator  */
+    DW_AT_GNU_numerator = 0x2303,
+    DW_AT_GNU_denominator = 0x2304,
+    /* https://gcc.gnu.org/wiki/DW_AT_GNU_bias  */
+    DW_AT_GNU_bias = 0x2305,
+
     DW_AT_hi_user = 0x3fff
   };

But I want to make sure we get the type/signedness right.

Could you help me with creating gnat examples that compile and show their
usage?

If I try to compile your example I get two warnings:

tt.adb:4:04: warning: size clause forces biased representation for "Small"
tt.adb:8:03: warning: size clause forces biased representation for
"Repeat_Count_T"

Are those expected?

Also the subranges come out as:

 [    4e]      subrange_type        abbrev: 3
               lower_bound          (sdata) -7
               upper_bound          (sdata) -4
               GNU_bias             (sdata) -7
               name                 (strp) "tt__small"
               type                 (ref4) [    8d]
 [    8d]    base_type            abbrev: 7
             byte_size            (data1) 1
             encoding             (data1) signed (5)
             name                 (strp) "tt__TsmallB"
             artificial           (flag_present) yes

and

 [    6d]      subrange_type        abbrev: 6
               upper_bound          (sdata) 64
               GNU_bias             (sdata) 1
               name                 (strp) "tt__repeat_count_t"
               type                 (ref4) [    94]
 [    94]    base_type            abbrev: 7
             byte_size            (data1) 1
             encoding             (data1) signed (5)
             name                 (strp) "tt__Trepeat_count_tB"
             artificial           (flag_present) yes

There are three things that surprised me about this.
First that the byte_size is 1, are these types really using a full byte and not
2 or 6 bits?
And second that the bias is on the subrange_type and not the base_type. Is that
intended?
Finally, why is the last type signed?

Also could you help me create an compilable example of
https://gcc.gnu.org/wiki/DW_AT_GNU_numerator_denominator

Thanks,

Mark

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