Re: [PATCH] Fix for the complaint observed when symbol reading due to unsupported .debug_names form.

Tom de Vries
2020-05-08T15:16:05Z

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On 08-05-2020 16:36, Tom de Vries wrote:
> On 07-05-2020 15:26, Tom Tromey wrote:
>>>>>>> ">" == nitachra <Nitika.Achra@amd.com> writes:
>>
>>>> Following complaint is observed with the executable compiled with -gdwarf-5
>>>> and -gpubnames flags- "During symbol reading: Unsupported .debug_names form
>>>> DW_FORM_ref4". This is the form corresponding to DW_IDX_die_offset attribute.
>>>> This patch fixes this complaint. Tested with clang 10.0.0. Test case used-
>>
>>>> int main()
>>>> {
>>>> int sum,a,b;
>>>> sum = a + b;
>>>> return sum;
>>>> }
>>
>> Does it fail some existing test in the gdb testsuite?
>
> I don't think so, that is, not unless you use:
> - clang as CC_FOR_TARGET, and
> - target board unix/-gdwarf-5/-gpubnames.
>
>> Normally what we like to see is either that a patch fixes some existing
>> failure (perhaps when the test suite is run in a certain way); or a new
>> test that fails before the patch and passes afterward.
>>
>
> I've add a dwarf assembly test-case for this (
> https://sourceware.org/pipermail/gdb-patches/2020-May/168244.html ).
>
> It should kfail without this patch, and pass with this patch (though it
> doesn't pass for me on openSUSE due to the problem described in PR25941).
>

So, if someone can verify that the test-case passes with this patch,
I'll commit.

Thanks,
- Tom

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Fix for the complaint observed when symbol reading due to unsupported .debug_names form

Following complaint is observed with the executable compiled with -gdwarf-5
and -gpubnames flags - "During symbol reading: Unsupported .debug_names form
DW_FORM_ref4". This is the form corresponding to DW_IDX_die_offset attribute.
This patch fixes this complaint. Tested with clang 10.0.0. Test case used -

int main()
{
int sum,a,b;
sum = a + b;
return sum;
}

clang -gdwarf-5 -gpubnames test.c -o test.out

gdb -q test.out -ex "set complaints 1" -ex "start"

Reading symbols from test.out...
During symbol reading: Unsupported .debug_names form DW_FORM_ref4 \
[in module test.out]
Temporary breakpoint 1 at 0x400484
Starting program: test.out
During symbol reading: Unsupported .debug_names form DW_FORM_ref4 \
[in module test.out]
During symbol reading: Unsupported .debug_names form DW_FORM_ref4 \
[in module test.out]
During symbol reading: Unsupported .debug_names form DW_FORM_ref4 \
[in module test.out]

gdb/dwarf2/ChangeLog:

2020-05-08 Nitika Achra <Nitika.Achra@amd.com>

PR symtab/25952
* read.c (dw2_debug_names_iterator::next): Handle DW_FORM_ref*
and DW_IDX_die_offset. If there is no compilation unit attribute in
the index entry, then there is a single CU. Return the CU at O index
of compilation unit vector.

gdb/testsuite/ChangeLog:

2020-05-08 Tom de Vries <tdevries@suse.de>

* gdb.dwarf2/clang-debug-names.exp: Remove PR25952 kfail.

---
gdb/dwarf2/read.c | 18 ++++++++++++++++++
gdb/testsuite/gdb.dwarf2/clang-debug-names.exp | 13 +------------
2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index ac208991ff..fc48bb6006 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -5352,6 +5352,18 @@ dw2_debug_names_iterator::next ()
ull = read_unsigned_leb128 (abfd, m_addr, &bytes_read);
m_addr += bytes_read;
break;
+ case DW_FORM_ref4:
+ ull = read_4_bytes (abfd, m_addr);
+ m_addr += 4;
+ break;
+ case DW_FORM_ref8:
+ ull = read_8_bytes (abfd, m_addr);
+ m_addr += 8;
+ break;
+ case DW_FORM_ref_sig8:
+ ull = read_8_bytes (abfd, m_addr);
+ m_addr += 8;
+ break;
default:
complaint (_("Unsupported .debug_names form %s [in module %s]"),
dwarf_form_name (attr.form),
@@ -5384,6 +5396,12 @@ dw2_debug_names_iterator::next ()
}
per_cu = &dwarf2_per_objfile->get_tu (ull)->per_cu;
break;
+ case DW_IDX_die_offset:
+ /* In a per-CU index (as opposed to a per-module index), index
+ entries without CU attribute implicitly refer to the single CU. */
+ if (per_cu == NULL)
+ per_cu = dwarf2_per_objfile->get_cu (0);
+ break;
case DW_IDX_GNU_internal:
if (!m_map.augmentation_is_gdb)
break;
diff --git a/gdb/testsuite/gdb.dwarf2/clang-debug-names.exp b/gdb/testsuite/gdb.dwarf2/clang-debug-names.exp
index 8bd60401c4..a6e33c1d89 100644
--- a/gdb/testsuite/gdb.dwarf2/clang-debug-names.exp
+++ b/gdb/testsuite/gdb.dwarf2/clang-debug-names.exp
@@ -142,15 +142,4 @@ set pass_re \
[multi_line \
$cmd \
"type = int \\(\\)"]
-set kfail_re \
- [multi_line \
- $cmd \
- "type = <unknown return type> \\(\\)"]
-gdb_test_multiple $cmd "" {
- -re -wrap $pass_re {
- pass $gdb_test_name
- }
- -re -wrap $kfail_re {
- kfail symtab/25952 $gdb_test_name
- }
-}
+gdb_test $cmd $pass_re