[Dwarf-Discuss] DWARF and source text embedding
eager at eagerm.com
Wed Jan 31 14:33:37 PST 2018
Hi Scott --
Please submit your proposal at http://dwarfstd.org/Comment.php.
On 01/31/2018 02:05 PM, scott at scottlinder.com wrote:
> Hello all,
> I am a compiler engineer at AMD, working on tools for debugging
> programs. The problem I am attempting to solve was brought up previously
> in the
> DWARF Standard issue 161018.1 titled "DWARF-embedded source for
> programs", and is the result of runtimes like OpenCL doing online
> in an environment where it is not desireable (or even feasible) to write
> sources to disk. In these cases, it would be useful to support embedding
> source directly in the resulting DWARF. I would like to propose a similar
> solution to the one outlined in the above issue, but without structural
> to the specification.
> Add two new optional fields to the file_names prologue of the line table.
> Section 126.96.36.199:
> Add two bullets after "5. DW_LNCT_MD5"
> 6. DW_LNCT_has_source
> DW_LNCT_has_source indicates that the value is a boolean which
> affects the
> interpretation of an accompanying DW_LNCT_source value. When
> present there
> must be an accompanying DW_LNCT_source value. When true, consumers
> may use
> the embedded source instead of attempting to discover the source on
> When false, consumers will ignore the DW_LNCT_source value. This
> code point
> is always paired with a flag form (e.g. DW_FORM_flag or
> 7. DW_LNCT_source
> DW_LNCT_source indicates that the value is a null-terminated string
> is the original source text of the file. When present there must be an
> accompanying DW_LNCT_has_source value. The string will contain the
> encoded source text with '\n' line endings. When the accompanying
> DW_LNCT_has_source value is false, the value of DW_LNCT_source will
> be the
> empty string. This code point is always paired with a string form
> DW_FORM_string, DW_FORM_line_strp, DW_FORM_strp).
> New type codes can be allocated for them in a backwards-compatible way, or
> codes for these new content types can be added in the range of
> [DW_LNCT_lo_user, DW_LNCT_hi_user] to avoid changing the spec itself.
> Table 7.27:
> Add DW_LNCT_has_source 0x6
> Add DW_LNCT_source 0x7
> Any DWARFv5 consumer which is unaware of this extension would continue to
> operate as before, ignoring the new fields. Any consumer which is aware
> of the
> extension would know to check DW_LNCT_has_source for each file_name
> entry in
> order to determine whether the embedded source field (DW_LNCT_source)
> the source text of the corresponding file.
> My team and I believe this simplifies the design by removing the need for
> changes to the compile unit sections, and by avoiding the addition of
> file_name_entry_formats in a single program, all without sacrificing any
> information. We have a preliminary implementation in LLVM/Clang, which
> embedding source (clang -gdwarf-5 -gembed-source) and inspecting it via
> llvm-dwarfdump and llvm-objdump (with the -source flag). The patches are
> available at https://reviews.llvm.org/D42765 (LLVM) and
> https://reviews.llvm.org/D42766 (Clang).
> I would like any and all feedback on the design, and want to see about the
> possibility of adding the new content type codes outside of the "user"
> (i.e. adding new entries for them in Table 7.27) in the next version of the
> Scott Linder
> Dwarf-Discuss mailing list
> Dwarf-Discuss at lists.dwarfstd.org
Michael Eager eager at eagerm.com
1960 Park Blvd., Palo Alto, CA 94306
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