[Dwarf-Discuss] DWARF and source text embedding
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
Re: [Dwarf-Discuss] DWARF and source text embedding
Hi Scott -- Please submit your proposal at http://dwarfstd.org/Comment.php. On 01/31/2018 02:05 PM, 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 -- Michael Eagerea...@eagerm.com 1960 Park Blvd., Palo Alto, CA 94306 ___ Dwarf-Discuss mailing list Dwarf-Discuss@lists.dwarfstd.org http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org
Re: [Dwarf-Discuss] DWARF and source text embedding
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
