sablevm-developer

[Sablevm-developer] Errno usage considered harmful?!

[Grzegorz B. P. <ga...@de...>]

Hi all,

I have strange problems with compiler warnings:

1. If I add:
  #include <errno.h>
  extern int errno;
I get such warning:
  java_lang_ProcessImpl.c:24: warning: function declaration isn't a
prototype

2. In interrupt() implementation I use a pointer to pthread_cond_t:
  volatile pthread_cond_t *sleeping_on_cond;
I also keep getting this warning:
  java_lang_VMThread.c:342: warning: passing arg 1 of
  `pthread_cond_broadcast' discards qualifiers from pointer target type
which is such code:
  pthread_cond_broadcast (env_other->thread.sleeping_on_cond);

Not sure how to deal with these two. Suggestions are very welcomed. [*]

Cheers,

				Grzegorz B. Prokopski

[*] Like a good RTFM, for ex.

-- 
Grzegorz B. Prokopski <ga...@de...>
Debian GNU/Linux      http://www.debian.org
SableVM - LGPLed JVM  http://www.sablevm.org
Why SableVM ?!?       http://devel.sablevm.org/wiki/WhySableVM

Re: [Sablevm-developer] Errno usage considered harmful?!

[Etienne G. <gag...@uq...>]

Hi Greg,

Grzegorz B. Prokopski wrote:
> 1. If I add:
>   #include <errno.h>
>   extern int errno;
> I get such warning:
>   java_lang_ProcessImpl.c:24: warning: function declaration isn't a
> prototype

You should NEVER declare errno.  #include <errno.h> declares it
appropriately.  (It can be a macro, of many things, specially when you
compile with multi-threading support).

> 2. In interrupt() implementation I use a pointer to pthread_cond_t:
>   volatile pthread_cond_t *sleeping_on_cond;
> I also keep getting this warning:
>   java_lang_VMThread.c:342: warning: passing arg 1 of
>   `pthread_cond_broadcast' discards qualifiers from pointer target type
> which is such code:
>   pthread_cond_broadcast (env_other->thread.sleeping_on_cond);

Why aren't you using SableVM's wrapper for broadcasting?  I think that
we should discuss your code in my office; it would be quicker than long
emails...

Etienne

-- 
Etienne M. Gagnon, Ph.D.             http://www.info.uqam.ca/~egagnon/
SableVM:                                       http://www.sablevm.org/
SableCC:                                       http://www.sablecc.org/

Re: [Sablevm-developer] Errno usage considered harmful?!

[Clark V. <cl...@CS...>]

I have some guesses, below.

-- 
ttfn,
clark
cl...@cs...


On Wed, 10 Mar 2004, Grzegorz B. Prokopski wrote:

> Hi all,
> 
> I have strange problems with compiler warnings:
> 
> 1. If I add:
>   #include <errno.h>
>   extern int errno;
> I get such warning:
>   java_lang_ProcessImpl.c:24: warning: function declaration isn't a
> prototype

It would help to know which line is line 24, but here's something that may
be worth checking:  Although the extern declaration should be fine, errno
may be declared as a macro rather than a simple variable --- particularly
with multithreaded code, where errno's exist for each separate thread.  
Try just using the include and removing the "extern int errno;" statement.

> 2. In interrupt() implementation I use a pointer to pthread_cond_t:
>   volatile pthread_cond_t *sleeping_on_cond;
> I also keep getting this warning:
>   java_lang_VMThread.c:342: warning: passing arg 1 of
>   `pthread_cond_broadcast' discards qualifiers from pointer target type
> which is such code:
>   pthread_cond_broadcast (env_other->thread.sleeping_on_cond);

The prototype for cond_broadcast doesn't expect a volatile type for the
argument, so that qualifier is being discarded when you call the function.
An explicit cast may eliminate the warning, but the problem is that the
cond_broadcast code was not compiled assuming volatile input arguments.  
If that's a problem then you'll need to re-examine why you need volatile
in sleeping_on_cond.

> Not sure how to deal with these two. Suggestions are very welcomed. [*]
> 
> Cheers,
> 
> 				Grzegorz B. Prokopski
> 
> [*] Like a good RTFM, for ex.
> 
> 

Re: [Sablevm-developer] Errno usage considered harmful?!

[Grzegorz B. P. <ga...@de...>]

W li=B6cie z =B6ro, 10-03-2004, godz. 08:26, Clark VERBRUGGE pisze:=20
> I have some guesses, below.
> Try just using the include and removing the "extern int errno;"
> statement.

Works, indeed.

> > 2. In interrupt() implementation I use a pointer to pthread_cond_t:
> >   volatile pthread_cond_t *sleeping_on_cond;
> > I also keep getting this warning:
> >   java_lang_VMThread.c:342: warning: passing arg 1 of
> >   `pthread_cond_broadcast' discards qualifiers from pointer target
> type
> > which is such code:
> >   pthread_cond_broadcast (env_other->thread.sleeping_on_cond);
>=20
> The prototype for cond_broadcast doesn't expect a volatile type for
>  the argument, so that qualifier is being discarded when you call the
>  function.
> An explicit cast may eliminate the warning, but the problem is that
>  the cond_broadcast code was not compiled assuming volatile input
>  arguments. =20
>=20
> If that's a problem then you'll need to re-examine why you need
>  volatile in sleeping_on_cond.

Good hint. The problem was, that I wanted volatile _pointer_ to
pthread_cond_t, not a pointer to volatile pthread_cond_t.
I changed the declaration to sth. like:

	pthread_cond_t *volatile sleeping_on_cond;

and the warnings are all gone.

Thanks a lot,

				Grzegorz B. Prokopski

--=20
Grzegorz B. Prokopski <ga...@de...>
Debian GNU/Linux      http://www.debian.org
SableVM - LGPLed JVM  http://www.sablevm.org
Why SableVM ?!?       http://devel.sablevm.org/wiki/WhySableVM

Re: [Sablevm-developer] Errno usage considered harmful?!

[Stephen C. <s1...@me...>]

"Grzegorz B. Prokopski" <ga...@de...> writes:

> 1. If I add:
>   #include <errno.h>
>   extern int errno;
> I get such warning:
>   java_lang_ProcessImpl.c:24: warning: function declaration isn't a
> prototype

If you are really concerned about systems whose errno.h doesn't
declare errno, wrap the variable declaration in a !defined(errno)
check.  This is what bash (not to mention GNU errno.h) does.  I
suppose you'd get a warning if you had -Wredundant-decls on and
weren't building with threads, but I don't think you do.

On GNU, when you are using threads, errno expands to a function call
(__errno_location) that returns a pointer, which is then dereferenced.

--
Stephen Compall or s11 or sirian

The best thing about growing older is that it takes such a long time.

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