[Dwarf-Discuss] Asm syntax for DWARF 5 line table info

David Blaikie dblaikie at gmail.com
Fri Jun 15 12:25:23 PDT 2018


FWIW - if we're talking about assembly extensions, another one LLVM could
use (it currently is one of the few things where Clang's integrated
assembler can emit object code that can't be represented via textual
assembly output) is the ability to express multiple line tables in a single
assembly file. LLVM uses this in LTO situations, where a single object file
contains the code to more than one source file.

On Fri, Jun 15, 2018 at 4:57 AM Paul Robinson via Dwarf-Discuss <
dwarf-discuss at lists.dwarfstd.org> wrote:

> cc binutils
>
> > -----Original Message-----
> > From: Nick Clifton [mailto:nickc at redhat.com]
> > Sent: Friday, June 15, 2018 6:18 AM
> > To: Robinson, Paul; dwarf-discuss at lists.dwarfstd.org
> > Subject: Re: [Dwarf-Discuss] Asm syntax for DWARF 5 line table info
> >
> > Hi Paul,
> >
> > > I have been working on adding DWARF 5 support to LLVM, and some of
> > > that support requires some assembler syntax tweaks.  It has been
> > > suggested that I publicize those tweaks outside of the LLVM world,
> > > and this list seems like the most likely place to find the people
> > > who would be most interested in agreeing on a common syntax.
> >
> > I think that it would also be wise to include the binutils project
> > (binutils at sourceware.org) as they are responsible for the GNU
> > Assembler (gas).
> >
> > > I propose to add a new optional clause to the .file directive, like so:
> > >
> > >     .file filenumber [ "directory" ] "path" [ md5 checksum ]
> > >
> > > where md5 is a keyword and checksum is the integer checksum,
> > > typically expressed as a hex 128-bit value.
> > >
> > > If all .file directives provide an md5 checksum, then the assembler
> > > will put that checksum into the DWARF 5 file table.
> >
> > If there are discrepancies in the md5 checksums, what should the
> assembler
> > do ?
>
> In LLVM, I have the assembler issue a warning if it sees inconsistent use
> of the md5 clause.  It's not an error, because I do see it happen when
> the compiler is reading a preprocessed file, and the assembler can't tell
> the difference between something the compiler produced and a mistake made
> by human coding.
>
> Thanks,
> --paulr
>
> >
> > Cheers
> >   Nick
> >
> >
>
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