[Dwarf-Discuss] Is this legal DWARF, and if so, what does it mean?
eager at eagercon.com
Mon Sep 15 10:56:09 PDT 2014
On 09/15/14 10:32, John DelSignore wrote:
> TotalView has a customer that has C++ code that produces the following DWARF with the Intel 12.1
ICC generates a lot of idiosyncratic DWARF.
> <0><1192a2>: Abbrev Number: 1 (DW_TAG_compile_unit)
> DW_AT_comp_dir : ...SNIPPED...
> DW_AT_language : 4 (C++)
> DW_AT_name : ...SNIPPED...
> DW_AT_producer : Intel(R) C++ Intel(R) 64 Compiler XE for applications running on Intel(R)
> 64, Version 12.1 Build 20110811
> Fixes SameLinkageName MemberPointers
> DW_AT_stmt_list : 0x5d20
> <1><119376>: Abbrev Number: 2 (DW_TAG_namespace)
> DW_AT_name : std
> <2><268209>: Abbrev Number: 37 (DW_TAG_lexical_block)
> DW_AT_decl_line : 1301
> DW_AT_decl_column : 79
> DW_AT_decl_file : 1
> DW_AT_low_pc : 0xb02a1
> DW_AT_high_pc : 0xb02d4
> <3><26821e>: Abbrev Number: 38 (DW_TAG_lexical_block)
> DW_AT_decl_line : 1351
> DW_AT_decl_column : 31
> DW_AT_decl_file : 1
> DW_AT_low_pc : 0xb03a7
> DW_AT_high_pc : 0xb03f7
> <2><268234>: Abbrev Number: 16 (DW_TAG_inlined_subroutine)
> 1. The lexical block at <268209> is at "std" namespace scope. What does it mean to have a lexical
> block at namespace scope? Note that that lexical block contains /only/ another lexical block at
> <26821e>; no subroutines or variables.
Looks unnecessary to me. Do you have the source for this file?
I guess this might be generated if you had something like
/* whatever */
But my guess is that the original source did not look like this.
> 2. The lexical block at <26821e> has an address range that is not nested inside its containing
> lexical block's address range. Is that legal, and if so, what does that mean? Note that that
> lexical block contains nothing else; no subroutines, blocks, or variables.
Maybe legal. The DWARF tree indicates the static nesting. If a compiler generated
code/data for a nested scope at a different location from the containing scope, then
maybe it might describe the lexical block with a different address range.
Since the lexical block is empty, I'm not sure that this really has any meaning.
ICC does a significant amount of code movement during optimization. I think
that it doesn't clean up all of the DWARF when it moves code and is accidentally
leaving a now-empty lexical block behind.
Michael Eager eager at eagercon.com
1960 Park Blvd., Palo Alto, CA 94306 650-325-8077
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