> So the main question is why is anything that is indexing the current CU only,
> accessing anything from another CU? It can't and shouldn't. That is the bug.
Indexing is accessing another CU because there is a reference (offset) to
another CU.
For example, in the 2nd compile unit below, the DW_AT_type of
DW_TAG_formal_parameter at offset 0x1772 is referencing the 1st compile unit
(offset 0x1741).
Compilation Unit @ offset 0x16f9:
Length: 0x4c (32-bit)
Version: 4
Abbrev Offset: 0x763
Pointer Size: 4
<0><1704>: Abbrev Number: 1 (DW_TAG_compile_unit)
<1705> DW_AT_producer : (indirect string, offset: 0x0): clang version
3.9.0 (trunk)
<1709> DW_AT_language : 12 (ANSI C99)
<170b> DW_AT_name : (indirect string, offset: 0x4be): main.c
<170f> DW_AT_stmt_list : 0x1329
<1713> DW_AT_comp_dir : (indirect string, offset: 0x4c5):
C:\Users\phlav\Documents\opus studio 2013\Projects\OpusProject9
<1717> Unknown AT value: 3fe1: 1
<1717> DW_AT_low_pc : 0x400000
<171b> DW_AT_high_pc : 0x8
<1><171f>: Abbrev Number: 2 (DW_TAG_subprogram)
<1720> DW_AT_low_pc : 0x400000
<1724> DW_AT_high_pc : 0x8
<1728> Unknown AT value: 3fe7: 1
<1728> DW_AT_frame_base : 1 byte block: 51 (DW_OP_reg1 (r1))
<172a> DW_AT_name : (indirect string, offset: 0xab): main
<172e> DW_AT_decl_file : 1
<172f> DW_AT_decl_line : 4
<1730> DW_AT_type : <0x1741>
<1734> DW_AT_external : 1
<1734> Unknown AT value: 3fe1: 1
<2><1734>: Abbrev Number: 3 (DW_TAG_variable)
<1735> DW_AT_const_value : 55
<1736> DW_AT_name : (indirect string, offset: 0xd9): x
<173a> DW_AT_decl_file : 1
<173b> DW_AT_decl_line : 7
<173c> DW_AT_type : <0x1741>
<1><1741>: Abbrev Number: 4 (DW_TAG_base_type)
<1742> DW_AT_name : (indirect string, offset: 0x8f): int
<1746> DW_AT_encoding : 5 (signed)
<1747> DW_AT_byte_size : 4
Compilation Unit @ offset 0x1749:
Length: 0x32 (32-bit)
Version: 4
Abbrev Offset: 0x763
Pointer Size: 4
<0><1754>: Abbrev Number: 5 (DW_TAG_compile_unit)
<1755> DW_AT_producer : (indirect string, offset: 0x0): clang version
3.9.0 (trunk)
<1759> DW_AT_language : 12 (ANSI C99)
<175b> DW_AT_name : (indirect string, offset: 0x505): Source1.c
<175f> DW_AT_stmt_list : 0x1362
<1763> DW_AT_comp_dir : (indirect string, offset: 0x50f):
C:\Users\phlav\Documents\opus studio 2013\Projects\OpusLibrary
<1767> Unknown AT value: 3fe1: 1
<1><1767>: Abbrev Number: 6 (DW_TAG_subprogram)
<1768> DW_AT_name : (indirect string, offset: 0x54e): lib
<176c> DW_AT_decl_file : 1
<176d> DW_AT_decl_line : 3
<176e> DW_AT_prototyped : 1
<176e> DW_AT_type : <0x1741>
<1772> DW_AT_external : 1
<1772> Unknown AT value: 3fe1: 1
<2><1772>: Abbrev Number: 7 (DW_TAG_formal_parameter)
<1773> DW_AT_name : (indirect string, offset: 0xd9): x
<1777> DW_AT_decl_file : 1
<1778> DW_AT_decl_line : 3
<1779> DW_AT_type : <0x1741>
________________________________________
From: Greg Clayton [[email protected]]
Sent: Friday, April 29, 2016 2:02 PM
To: Philippe Lavoie
Cc: [email protected]
Subject: Re: [lldb-dev] LTO debug info
> On Apr 28, 2016, at 8:11 AM, Philippe Lavoie <[email protected]>
> wrote:
>
>
> What made me suspect a data corruption issue were asserts triggered in the
> VC++ vector implementation when we use an LTO binary with a DEBUG lldb build
> on Windows.
>
> For example,
> at source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.cpp:624,
>
> File: C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\INCLUDE\vector
> Line: 240
> Expression: vector iterators incompatible
>
> Digging deeper, the assertion is triggered by accesses to
> DWARFCompileUnit::m_die_array
>
> In the 'parser_fn' lambda in SymbolFileDWARF::Index() that indexes each
> compile unit in parallel, DWARFCompileUnit::ExtractDIEsIfNeeded(..) ,
> DWARFCompileUnit::Index(..) and DWARFCompileUnit::ClearDIEs() are called in
> sequence.
>
> 'ExtractDIEsIfNeeded' and 'ClearDIEs' respectively populates and clears
> DWARFCompileUnit::m_die_array.
>
> But when DWARFCompileUnit::Index(..) looks up a DIE in another CU and that CU
> is running 'ExtractDIEsIfNeeded' or 'ClearDIEs', it will access a stale or
> invalid DWARFCompileUnit::m_die_array ...
So the main question is why is anything that is indexing the current CU only,
accessing anything from another CU? It can't and shouldn't. That is the bug.
> -Philippe
>
> ________________________________________
> From: Greg Clayton [[email protected]]
> Sent: Monday, April 25, 2016 7:59 PM
> To: Philippe Lavoie
> Cc: [email protected]
> Subject: Re: [lldb-dev] LTO debug info
>
>> On Apr 25, 2016, at 1:37 PM, Philippe Lavoie via lldb-dev
>> <[email protected]> wrote:
>>
>> Hello,
>>
>> We noticed an issue with dwarf parsing when debugging a large application
>> compiled with LTO.
>>
>> Since an LTO application's debug info can have inter-compile-unit
>> references, (for example: a type defined in one compile-unit and used in
>> another) we noticed that the "m_type_index" vector in SymbolFileDWARF can
>> get corrupted. This is because many index structures in SymbolFileDWARF are
>> generated in parallel.
>>
>> Is is a bug or is it expected to be the compiler's/linker's job to generate
>> self-contained DWARF data without inter-CU references?
>>
>> -Philippe
>
> TEach SymbolFileDWARF should generate its own accelerator tables in a self
> contained way. No SymbolFileDWARF should be adding references to their
> accelerator maps that actually refer to DIEs from another SymbolFileDWARF. We
> might need to look at the indexing function that make sure if they see and
> DW_FORM_ref_addr attributes, that they don't add any of them to their index.
> That seems like the bug?
>
> Greg
>
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