Re: Very interesting IA64 gas bug

["H. J. Lu" <hjl at lucon dot org>]

On Fri, Jun 06, 2003 at 04:14:12PM -0700, Jim Wilson wrote:
> I don't see any problem with the buffer itself.  However, there is a 
> problem with the parsing algorithm in do_scrub_chars.
> 
> do_scrub_chars tries to eliminate whitespace between arguments.  It 
> assumes that it is starting at the beginning of a line, and that a line 
> looks like "label: opcode arguments" where label is optional.  IA-64 
> instructions do not look like this, because we have qualifying 
> predicates before the opcode, e.g. (p7).  This happens to work by 
> accident with the current parsing code because ( and ) are not symbol 
> characters, so do_scrub_chars assumes it is neither the label nor opcode 
> and passes it through unchanged without changing state.
> 
> The problem occurs if a buffer ends in the middle of a qualifying 
> predicate (qp).  The first buffer sees "(p" at the end, and because it 
> is at the end of the buffer, it stops in the middle of the qp and 
> switches to state 11 which means this may be a label.  When we start the 
> next buffer, we switch to state 3 (after the opcode) because there was 
> no colon.  The "hint" is then parsed as an argument, and we eliminate 
> the space after it, and now we have an unknown opcode hint@pause.
> 
> This could be fixed by adding a new state for parsing IA-64 qps.  If we 
> see an open paren before the opcode, then we switch to the new state, 
> and switch back to state 0 after seeing the ).

I tried it. It still doesn't work in all cases. I am enclosing a patch
and testsuite here.

# make src
./buffer
# make
./as   -o buffer00.o buffer00.s
./as   -o buffer01.o buffer01.s
./as   -o buffer02.o buffer02.s
./as   -o buffer03.o buffer03.s
./as   -o buffer04.o buffer04.s
./as   -o buffer05.o buffer05.s
buffer05.s: Assembler messages:
buffer05.s:32753: Warning: end of file not at end of a line; newline inserted
./as   -o buffer06.o buffer06.s
./as   -o buffer07.o buffer07.s
./as   -o buffer08.o buffer08.s
./as   -o buffer09.o buffer09.s
./as   -o buffer10.o buffer10.s
./as   -o buffer11.o buffer11.s
buffer11.s: Assembler messages:
buffer11.s:32760: Error: Unknown opcode `hint@pause'
make: *** [buffer11.o] Error 1

I think input/output buffer handling has some problems.

> 
> Alternatively, we could give up and decide that do_scrub_chars can't 
> know all details of all target assembler syntaxes, and hence shouldn't 
> be trying to delete spaces between arguments.  It should only eliminate 
> duplicate whitespace.  This would make porting to oddball targets 
> slightly easier, and maintenance of do_scrub_chars easier.  It may 
> require modifying some targets to handle whitespace in arguments though.

I am afraid to break all the other targets.


H.J.

Attachment: gas-buffer.patch
Description: Text document

Attachment: bug.tar.gz
Description: GNU Zip compressed data