[lldb-dev] [PATCH] Use 0 as LLDB_INVALID_LINE_NUMBER

[Andrew MacPherson]

Ok, that makes sense, I should have provided more context.

We use LLVM's DIBuilder to add debug info to our JITed KL language and
there are certain functions we provide which are internal and for which we
don't want to provide line info. We want these functions to show up named
in stack traces but would prefer to not have file and line info show up. We
have been passing 0 as the line number for these functions (DIBuilder's
createFunction() requires a line number) which makes them behave as we want
in gdb, however in LLDB they show up coming from our dummy internal file
name on line 0.

This isn't a big deal but would be nice to fix, the one which prompted us
to look into this though was around stepping. In gdb these internal
functions are skipped by default because they have no source and line info,
whereas when stepping in LLDB (with the avoids-no-debug flags set) stepping
still hits these functions even though there's no source available for
them, which we'd like to avoid.

Taking another look maybe the correct fix would be to modify
LineEntry::IsValid() to add a check for line != 0 too?

Thanks,
Andrew


On Fri, Mar 14, 2014 at 7:29 PM, Greg Clayton <gclayton at apple.com> wrote:

> I agree with Jim in that it is nice to know when a compiler told us line
> 0, versus "invalid info" where UINT32_MAX is the value. I would vote to
> leave things as is unless you have a convincing argument otherwise.
>
>
> On Mar 14, 2014, at 11:21 AM, jingham at apple.com wrote:
>
> > lldb uses LLDB_INVALID_LINE_NUMBER to mean line number information is
> not available, and 0 to mean this is code that was generated by the
> compiler, but is artificial.  That's the way clang marks code (e.g. junk
> generated by ARC) that lldb will need to step through, or whatever, but
> should not show to the user.
> >
> > That's a useful distinction, and I'd like to maintain it.  What bad
> behavior are you seeing based on this?
> >
> > Jim
> >
> > On Mar 14, 2014, at 1:49 AM, Andrew MacPherson <andrew.macp at gmail.com>
> wrote:
> >
> >> gdb assumes that any debug entry with a line number of 0 means that
> line number information is not available (see struct symtab_and_line here):
> >>
> >> http://www.opensource.apple.com/source/gdb/gdb-967/src/gdb/symtab.h
> >>
> >> lldb currently uses UINT32_MAX for the same thing.
> >>
> >> I suggest changing lldb to use the same value as gdb so that it's
> possible to mark line entry data as invalid in the same way for both
> debuggers.
> >>
> >> Thanks,
> >> Andrew
> >>
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