bug#13775: 24.3.50; Omissions in documentation for crash reporting

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 22 Feb 2013 05:31:55 +0400
> From: Dmitry Gutov <dgutov@yandex.ru>
> CC: 13775@debbugs.gnu.org
> 
> > There's no way we can teach everybody the basics of GNU-style
> > configure scripts, including how to discover the available switches
> > and override compiler and linker options.  You need to learn that\
> 
> If by discovering switches you mean calling ./configure --help, then it 
> wasn't my problem.

I meant both the switches of configure and the compiler/linker
switches and options.

> The ./configure --help output tells how to override switches in general, 
> my complaint is about insufficient detail. Is the "Some influential 
> environment variables" part provided by autoconf or somesuch?

I don't understand the question.  The relevant part of the help text
is this:

  Some influential environment variables:
    CC          C compiler command
    CFLAGS      C compiler flags
    LDFLAGS     linker flags, e.g. -L<lib dir> if you have libraries in a
		nonstandard directory <lib dir>
    LIBS        libraries to pass to the linker, e.g. -l<library>
    CPPFLAGS    (Objective) C/C++ preprocessor flags, e.g. -I<include dir> if
		you have headers in a nonstandard directory <include dir>
    CPP         C preprocessor
    XMKMF       Path to xmkmf, Makefile generator for X Window System

  Use these variables to override the choices made by `configure' or to help
  it to find libraries and programs with nonstandard names/locations.

Which part(s) of this are unclear?

In any case, this is a standard text shown by every configure script
out there, so if you think it should be clarified, please complain to
the Autoconf developers.

> >> 1. Calling `xbacktrace' requires src/.gdbinit to be loaded. It
> >> a) requires the user to run gdb exactly from src/ (not `gdb src/emacs'),
> >
> > The file etc/DEBUG tells you that at the beginning:
> >
> >    ** When you debug Emacs with GDB, you should start it in the directory
> >    where the executable was made.  That directory has a .gdbinit file
> >    that defines various "user-defined" commands for debugging Emacs.
> >    (These commands are described below under "Examining Lisp object
> >    values" and "Debugging Emacs Redisplay problems".)
> 
> Um, yes, I read that. Maybe I should've skipped this part of the 
> complaint. But is this exact wording ("the directory where the 
> executable was made") important? If it just said "./src", that would be 
> more obvious.

I added that (revision 111290 on the emacs-24 branch).

> >> b) requires them to modify the `auto-load safe-path', or that .gdbinit
> >> is ignored.
> >
> > This "feature" entered GDB only recently.  Versions of GDB before 7.5
> > don't need that, and will barf if you use this command.  I don't see
> > any reasonable way of dealing with this without confusing newbies even
> > more (while veteran GDB users already know how to negotiate this
> > obstacle).
> 
> If the feature isn't considered for removal, this argument will become 
> less and less important over time. And the odds of a newbie being 
> confused by safe-path will approach 100%.

But GDB already tells you how to allow .gdbinit to be auto-loaded, and
also points to the GDB manual.  If the text displayed by GDB is not
clear or confusing, I suggest to report that to GDB maintainers.

> I'm not specifically asking to list the exact commands or ~/.gdbinit 
> contents to work around safe-path. Maybe just mention the feature and, 
> optionally, suggest consulting GDB manual, if that isn't obvious 
> already?

I added that to etc/DEBUG.

> But specifying exactly what to do if GDB version is >= 7.5 
> would also work.

That's hard to do, because the solution depends on the end-user's
preferences regarding security and on the degree of their machine's
exposure to other users and to the outside world.  The GDB manual
discusses the possible solutions, so a pointer to it will allow the
user to make up her mind.

> >> a) Do I set the variable when calling `make', or do I have to re-run
> >> ./configure? Not obvious, the answer is "the latter".
> >
> > Actually, both will work.
> 
> Not exactly.
> 
> 'CFLAGS="-g3" ./configure' works.
> 'CFLAGS="-g3" make' doesn't.
> 
> 'make CFLAGS="-g3"' does work, but AFAIK that's not the usual way of 
> binding an environment variable value.

CFLAGS is a Make variable.  Make normally initializes all its
variables by looking at the environment.  But 'CFLAGS="-g3" make'
doesn't export the value of CFLAGS for Make to see it, it only inserts
CFLAGS into the shell's own environment.  That is why the command
'CFLAGS="-g3" make' doesn't work, while 'make CFLAGS="-g3"' does.

This is all standard shell and Make stuff, I don't think it's
reasonable to expect Emacs documentation to teach all that.

> I think "compile without optimizations" or "compile for debugging" is a 
> sufficiently common special case to warrant listing the recommended 
> command somewhere in etc/DEBUG. That will take a few lines at the most.

It's already there, it just didn't mention the -O0 option explicitly;
I added that.  (Again, this is a basic compiler option, not something
specific to Emacs.)