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From: meissner@osf.org
Newsgroups: comp.compilers
Subject: Re: yacc & dbx
Keywords: yacc, debug
Message-ID: <9101311952.AA05132@curley.osf.org>
Date: 31 Jan 91 19:52:38 GMT
References: <299@ptcburp.ptcbu.oz.au>
Sender: compilers-sender@iecc.cambridge.ma.us
Reply-To: meissner@osf.org
Organization: Compilers Central
Lines: 71
Approved: compilers@iecc.cambridge.ma.us

| htf@castle.edinburgh.ac.uk (H T Fallside) writes:
| 
| >Anyone have any suggestions about ways of getting dbx to behave sensibly
| >with a yacc generated parser as part of the program - ie indexing into the
| >source during debug ?

Michael Henning writes:
 
| There is not necessarily any sensible way to deal with #line directives in
| the generated .c file. The easiest thing is usually to pre-process the
| generated code with sed or some other tool to remove the #line directives
| before compilation.

And John writes:

| [My experience is quite different; I've found it quite useful to put in
| breakpoints and single step by line in the .y file.  If you don't like the
| #line directives, the -l flag to yacc prevents them. -John]

It depends on what your object format is, whether it can handle #line
directives or not.  There are two inter-related problems -- whether
multiple files are handled within one object file format, and whether
line numbers within a function can vary outside of the range of the
function's start/end (or even if they must be monotonically
increasing).  Typical parser generators, require changing both the
filename and line number within a function to switch between the
actions and rules files.

Going over the object files I've dealt with in the past gives:

1.  Berkeley stabs
==================
This allows multiple .file and/or .line directives.


2.  System V.[0123] coff
========================
Pure COFF only allows one file in a compilation unit.  Line numbers
are relative to the start of the function, and must be positive, which
makes debugging inlines a pain as well.


3.  Third Eye ECOFF (used on MIPS)
==================================
ECOFF allows multiple files within a compilation unit, though you
cannot change the file within a function boundary.  Line numbers are
relative to the start of the function, though negative values are
allowed.  You must not have more than 65K of lines separating two
adjacent statements.


4.  OSF/rose
============
At present, we use Berkeley stabs and do not have a problem.


5.  Dwarf (System V.4)
======================
I can't find in my dwarf documents whether this is allowed or not,
though I remember a comment about trying to remove the restriction
that lines for a file be contigous, which would mean that you possibly
would have to have a separate file section for each #line that
introduced a filename, different from the previous.


--
Michael Meissner	email: meissner@osf.org		phone: 617-621-8861
Open Software Foundation, 11 Cambridge Center, Cambridge, MA, 02142
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