Re: libstdc++/5198: 3.0.3 linux x m68k build fail: invalid opcodes in c++locale.cc

["Aaron J. Grier" <aaron at frye dot com>]

The following reply was made to PR libstdc++/5198; it has been noted by GNATS.

From: "Aaron J. Grier" <aaron@frye.com>
To: Don Lindsay <lindsayd@cisco.com>
Cc: rodrigc@gcc.gnu.org, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org,
        nobody@gcc.gnu.org, gcc-gnats@gcc.gnu.org
Subject: Re: libstdc++/5198: 3.0.3 linux x m68k build fail: invalid opcodes in c++locale.cc
Date: Fri, 4 Jan 2002 14:34:11 -0800

 On Fri, Jan 04, 2002 at 01:53:00PM -0800, Don Lindsay wrote:
 
 > I see two questions:
 >  - should the makefile be specifying -m68000?
 > 	(I'm out of practice on multilib rules, but I think the
 > 	MULTILIB_* stuff is asking for just that, and means to.)
 
 as far as I understand it, yes, since we're multilibbing here.
 
 >  - given that -m68000 was on the command line, how come the assembler
 > 	output contains "casl" opcodes, which "as" tells us are only
 > 	present on the 68020 and up?
 >
 > I'm guessing that cc1 has to be fixed to not emit "casl" when invoked with
 > -m68000.
 
 the fault is with libstdc++-v3, specifically
 
 libstdc++-v3/config/cpu/m68k/bits/atomicity.h
 
 which includes "cas" as an inlined assembly instruction in a supposedly
 generic m68k include file.
 
 I've been able to identify at least three cases that need to be covered
 in atomicity.h:
 
 68020/30/40: use current "cas"
 mcpu32 and v4 coldfire: "tas" on a static local variable
 68000/010, v2/3 coldfire: disable interrupts
 
 disabling interrupts is rather heavy-handed, but I can't think of any
 other options for members of the m68k family that don't have
 test-and-set instructions.  we don't know a priori how many threads will
 be waiting, so we can't use peterson's counting solution.  (someone
 correct me if I'm wrong...)  I'm also no m68k guru, and am not sure how
 many members of the m68k family gcc differentiates between, so the above
 list of cases may not be complete.
 
 I'm preparing a quick-and-dirty patch for people to go over, but if
 someone beats me to it, more power to them.  :)
 
 -- 
   Aaron J. Grier  |   Frye Electronics, Tigard, OR   |  aaron@frye.com
      "In a few thousand years people will be scratching their heads
        wondering how on earth the first computer was invented and
           bootstrapped without a prior computer to do it with."
                     --  Chris Malcolm, on comp.arch