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Re: [PATCH] libdw: fix offset for sig8 lookup in dwarf_formref_die
- From: Josh Stone <jistone at redhat dot com>
- To: elfutils-devel at lists dot fedorahosted dot org
- Date: Wed, 14 Jan 2015 09:59:36 -0800
- Subject: Re: [PATCH] libdw: fix offset for sig8 lookup in dwarf_formref_die
On 01/14/2015 08:47 AM, Mark Wielaard wrote:
> On Wed, 2015-01-14 at 09:26 -0500, Jason P. Leasure wrote:
>> The type_offset of a type unit header is relative to the beginning
>> of the type unit header.
>> Signed-off-by: Jason P. Leasure <firstname.lastname@example.org>
>> libdw/dwarf_formref_die.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>> diff --git a/libdw/dwarf_formref_die.c b/libdw/dwarf_formref_die.c
>> index 63f6697..8b92e22 100644
>> --- a/libdw/dwarf_formref_die.c
>> +++ b/libdw/dwarf_formref_die.c
>> @@ -95,7 +95,7 @@ dwarf_formref_die (attr, result)
>> datap = cu->dbg->sectiondata[IDX_debug_types]->d_buf;
>> size = cu->dbg->sectiondata[IDX_debug_types]->d_size;
>> - offset = cu->type_offset;
>> + offset = cu->start + cu->type_offset;
> Thanks, I believe this is correct. I am surprised we didn't encounter
> this earlier. Do you happen to have a testcase for it?
It's a regression from commit 9202665816763, before which cu->start was
used with the offset everywhere.
I can see this in my dwarvish tool with Jason's example source. You
just need a ref_sig8 that's not in the first type_unit, cu->start > 0.
So here, struct A has a ref_sig8 to struct B in the second type_unit.
In the bad case I see "signature ref_sig8  0", where those last
two bits are supposed to be the offset and tag.
I see "signature ref_sig8  structure_type" with 0.160, or with
master and this patch, and it expands the tree of attributes from there.
Of course you won't want a GUI for tests, but it should be easy to craft
this one directly.