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

From: Dmitry Gutov
Subject: bug#13775: 24.3.50; Omissions in documentation for crash reporting
Date: Sat, 23 Feb 2013 01:53:43 +0400
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130215 Thunderbird/17.0.3

On 22.02.2013 13:24, Eli Zaretskii wrote:
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

You answered it below, "this is a standard text shown by ...".

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.

Thanks, maybe I'll do that, sometime.

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

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

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.

I see, I think.

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.)

Like I described, my difficulty here was that using "-O0" by itself is not enough, without "-g3" the resulting build is even less debuggable.

Omitting "-O0", leaving just "-g3", works, on the other hand, because the optimization is enabled by default due to the default CFLAGS value (AFAICT).

Anyway, you've addressed that in 111290, as well as two other items. Thank you, I'm considering this issue fixed.

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