[cfe-dev] Should -g1 mean -gline-tables-only?

[David Blaikie]

On Fri, Oct 17, 2014 at 11:39 AM, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Fri, Oct 17, 2014 at 11:32 AM, Hal Finkel <hfinkel at anl.gov> wrote:
>
>> ----- Original Message -----
>> > From: "David Blaikie" <dblaikie at gmail.com>
>> > To: "Hal Finkel" <hfinkel at anl.gov>
>> > Cc: "cfe-dev at cs.uiuc.edu Developers" <cfe-dev at cs.uiuc.edu>, "Eric
>> Christopher" <echristo at google.com>
>> > Sent: Friday, October 17, 2014 12:49:09 PM
>> > Subject: Re: Should -g1 mean -gline-tables-only?
>> >
>> > On Fri, Oct 17, 2014 at 10:37 AM, Hal Finkel < hfinkel at anl.gov >
>> > wrote:
>> >
>> >
>> > Hi,
>> >
>> > Debugging flags are not my area of expertise, but GCC's manual says
>> > about -g1:
>> >
>> > [from GCC's man page]
>> > Level 1 produces minimal information, enough for making backtraces in
>> > parts of the program that you don't plan to debug.
>> > This includes descriptions of functions and external variables, but
>> > no information about local variables and no line numbers.
>> >
>> >
>> >
>> > Sounds similar, apart from the "and external variables" part.
>> >
>> > It'd be interesting to actually look at the output - I Suspect it
>> > might be a bit more verbose than Clang's (or GCC's) -gmlt, maybe
>> > including namespaces, mangled function names, whatever else.
>> >
>> > I think maybe Google's GCC branch has -gmlt, but maybe it's not in
>> > GCC proper? I don't really know/understand.
>> >
>> >
>> > [end from GCC's man page]
>> >
>> > and IBM's manual for xlc says about -g1:
>> >
>> > [from IBM's man page]
>> > Generates minimal read-only debugging information about line numbers
>> > and source file names. No program state is preserved.
>> >
>> >
>> > Sounds about right. Be interesting to know if that's just the line
>> > table itself, or the inlining info that Clang's
>> > -gmlt/-gline-tables-only produces as well (yeah, -gline-tables-only
>> > is a bit of a half truth).
>>
>> How could I tell? (I believe we have some kind of dwarf-dumping utility,
>> but I don't know for what to look).
>>
>
> llvm-dwarfdump is a utility for dumping DWARF debug information. Running
> it on an object file built with xlc's -g1 and see if there are many DW_TAGs
> in the debug_info section (ones describing each function, etc). If the only
> thing of note is the line table (debug_line section) then it's probably not
> producing the inlining info that we do in -gmlt. *shrug*
>
> Anyway, it sounds like xlc's -g1 might be a bit less than Clang's -gmlt
> and GCC's -g1 might be a bit more than Clang's -gmlt. So if those are both
> valid interpretations of -g1, Clang's -gmlt should fit right in ;)
>

Hmm, well I tried a few things with GCC 4.8's -g1 and I couldn't get it to
produce debug info for a global (or namespaced) variable... so maybe the
docs are just wrong and it is -gmlt.


>
>
> - David
>
>
>>
>> Thanks again,
>> Hal
>>
>> >
>> >
>> > [end from IBM's man page]
>> >
>> > this sounds to me a lot like what -gline-tables-only does. Is there a
>> > reason we don't alias -g1 to -gline-tables-only? Currently, the code
>> > in Clang::ConstructJob treats it just like -g.
>> >
>> > Thanks again,
>> > Hal
>> >
>> > --
>> > Hal Finkel
>> > Assistant Computational Scientist
>> > Leadership Computing Facility
>> > Argonne National Laboratory
>> >
>> >
>>
>> --
>> Hal Finkel
>> Assistant Computational Scientist
>> Leadership Computing Facility
>> Argonne National Laboratory
>>
>
>
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