Re: [rfa/doc] correct info about best C++ compilers/debug formats

[David Carlton <carlton@math.stanford.edu>]

On Mon, 3 Feb 2003 12:56:22 -0600, Michael Elizabeth Chastain <mec@shout.net> said:

> After fixing the doco, we can kill all the setup_xfail_format dwarf-1
> lines.  We can either add a test for dwarf-1 to "skip_cplus_tests",
> or we can just let the test suite do its job and report a lot of
> FAILs on dwarf-1.  I favor the latter.  But I would like to discuss
> this *after* fixing the docs.

Fair enough.

> Now the content:

>  @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
>  proper compiler and the proper debug format.  Currently, @value{GDBN}
>  works best when debugging C@t{++} code that is compiled with
>  @value{NGCC} 2.95.3 or with @value{NGCC} 3.1 or newer, using the options
>  @option{-gdwarf-2} or @option{-gstabs+}.  DWARF 2 is preferred over
>  stabs; newer versions of @value{NGCC} use DWARF 2 as the default
>  whenever possible.  Other compilers and/or debug formats are likely to
>  work badly or not at all when using @value{GDBN} to debugg C@t{++} code.

> The normal spelling is 'DWARF2' not 'DWARF 2'.

I wondered about this.  The standard doesn't give any guidance (it
says "DWARF Version 2", to me DWARF 2 looks much better, and the GCC
option is -gdwarf-2, not -gdwarf2.  On the other hand, there are more
web pages that refer to it as DWARF2 than web pages that refer to it
as DWARF 2.

> Also you usually want to say "stabs+", not "stabs".

I guess that makes sense.

> Also a typo on "debugg".

Thanks.

> The part about "newer versions of gcc use DWARF 2 as the default
> whenever possible" is vague and not accurate enough for doco (I
> think).

Well, I wanted to include some sort of sentence that reassured users
that they probably didn't have to specify the debug format explicitly.
Also, if they use a recent version of GCC, they'll probably get
the best working debug format by default: if GCC doesn't default to
DWARF 2, there's probably a good reason for that.

> Some more places need changing:

>   To solve such problems, either recompile without optimizations, or use a
>   different debug info format, if the compiler supports several such
>   formats.  For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
>   supports the @samp{-gstabs} option.  @samp{-gstabs} produces debug info
>   in a format that is superior to formats such as COFF.  You may be able
>   to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
>   debug info.  See @ref{Debugging Options,,Options for Debugging Your
>   Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
>   information.

> --> Change "-gstabs" to "-gstabs+" here.  In particular "-gstabs" is
>       miserable with C++ (I have tested it).

>   For best results when using @sc{gnu} C@t{++}, use the stabs debugging
>   format.  You can select that format explicitly with the @code{g++}
>   command-line options @samp{-gstabs} or @samp{-gstabs+}.  See
>   @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
>   CC, gcc.info, Using @sc{gnu} CC}, for more information.

> --> Rewrite to say 'DWARF2'.

Thanks, I'll submit a revised patch including these.

David Carlton
carlton@math.stanford.edu