Hi Scott, Question: What does the DW_TAG_compile_unit look like for an embedded source file? For example, what does the DW_AT_name and DW_AT_comp_dir look like?
Cheers, John D. On 01/31/18 17:05, sc...@scottlinder.com wrote: > Hello all, > > I am a compiler engineer at AMD, working on tools for debugging > online-compiled > programs. The problem I am attempting to solve was brought up previously in > the > DWARF Standard issue 161018.1 titled "DWARF-embedded source for > online-compiled > programs", and is the result of runtimes like OpenCL doing online compilation > 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 the > 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 > changes > to the specification. > > ==== > > Add two new optional fields to the file_names prologue of the line table. > > Section 6.2.4.1: > 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 disk. > 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 > DW_FORM_flag_present). > 7. DW_LNCT_source > DW_LNCT_source indicates that the value is a null-terminated string which > 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 UTF-8 > 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 (e.g. > 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) contains > 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 multiple > file_name_entry_formats in a single program, all without sacrificing any > information. We have a preliminary implementation in LLVM/Clang, which > supports > 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" range > (i.e. adding new entries for them in Table 7.27) in the next version of the > specification. > > Regards, > Scott Linder > > _______________________________________________ > Dwarf-Discuss mailing list > Dwarf-Discuss@lists.dwarfstd.org > http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org > _______________________________________________ Dwarf-Discuss mailing list Dwarf-Discuss@lists.dwarfstd.org http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org
