RE: GDB/MI Output Syntax ambiguity

Xinan Tang
2004-08-24T17:15:37Z

Hi

If it is a shift/reduce conflict, you can ignore it if the shift is
your choice. By default the shift is a default action. If there is
reduce/reduce conflicts, then you need to start to worry.

--Xinan

-----Original Message-----
From: gdb-owner@sources.redhat.com [mailto:gdb-owner@sources.redhat.com]
On Behalf Of Bob Rossi
Sent: Monday, August 23, 2004 1:03 PM
To: gdb@sources.redhat.com
Subject: GDB/MI Output Syntax ambiguity

Hi,

I am generating a bottom up parser for 'GDB/MI Output Syntax' using
bison. Unfortunately, I think that I found an ambiguity, which makes it
not easily parsable. Please correct me if I am wrong.

output -> ( out-of-band-record )* [ result-record ]
"(gdb)" nl
result-record -> [ token ] "^" result-class ( "," result )* nl
out-of-band-record -> async-record | stream-record
async-record -> exec-async-output | status-async-output |
notify-asyn
exec-async-output -> [ token ] "*" async-output
status-async-output -> [ token ] "+" async-output
notify-async-output -> [ token ] "=" async-output

I am assuming that the grammar above for 'output' means that there can
be 0 or more 'out-of-band-record', followed by 0 or 1 'result-record',
followed by '(gdb)' and then a newline.

The problem is, when you are parsing 'output', and you get a 'token' as
the first token from the lexer, you don't know if that is part of the
'out-of-band-record' or if it is part of the 'result-record'. Both of
these rules optionally start with 'token'.Has anyone actually written a
recursive descent parser, or generated a parser from bison for GDB/MI's
output yet, or am I the first?

Help would be greatly appreciated. This is the only shift/reduce
conflict I have in my modified BNF version of the grammar. Other than
this, the grammar looks very well written.

I consider this to be a serious problem so I hope that I am not doing
something incorrectly or am mis-understanding the grammar.

Thanks,
Bob Rossi