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From: news@bungi.com.YorkU.CA
Newsgroups: comp.sys.nsc.32k
Subject: Re: Bug in minix library setjmp.s; lots of GNU tools diffs available
Message-ID: <9102072106.AA01016@manatee.UUCP>
Date: 8 Feb 91 02:06:52 GMT
References: <<9102071534.5947@munnari.oz.au>>
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> 
> Jyrki Kuoppala writes:
>  - When porting emacs to pc532-Minix, I noticed there's a bug in the
>  - setjmp library routine - it doesn't save registers r3-r7 (and f4-f7)
>  - which I think it should do.
[stuff deleted]

Ian write:
> I believe in ANSI C, there is no requirement to save registers in setjump.
> Variables which have to be accessed after the setjump should be marked
> volatile. Yes, some people have said that is ugly and nor the way it
> should be done, but I pretty sure, that is the way it is!

Some time back I ran into this setjump issue while trying to make all 
the 1.5.10 /usr/src/test programs run successfully.  In a nutshell I 
decided to set ANSI C aside and save all registers.  The essence of the 
decision was (1) that I have yet to run across a situation were saving 
all registers creates an adverse consequence (thats not to say they do 
not exist), (2) on numerious occasions not saving the registers has 
caused me a problem, and (3) in the large, the overhead of saving all 
registers is minimal.  

You might say I decided to switch rather than fight.  Alternatively, it 
might be argued that I put off the problem for someone else to solve.  
Never the less, this is one instance where I do not see the merit of 
strict ANSI C conformance.

My reading of ANSI C is that saving all registers is not in itself
a violation of the standard.  Rather that the consequence of doing so
may on occasion lead to unknowingly writing non-portable code (ie. code
that in someway depends upon setjmp saving all registers).

Considering that the setjump issue is a problem that we all share,
perhaps it would be useful for all of us to adopt a common solution.
That is, we collectively agree to (a) save all registers, or (b) 
actively go on a bug hunt :-).  Otherwise, this problem will 
continue to be a source of frustration, wasted time, generate message
traffic, etc.

Any thoughts pro or con ??

Obviously, my vote is for ignoring ANSI C and saving all registers --
that is unless someone makes a good case against.   


johnc

-- 
John Connin: manatee Orlando, Florida
         UUCP: {uunet,ge-dab,ucf-cs}!tarpit!tous!manatee!johnc