Date: Fri, 30 May 2003 20:02:06 +0200
From: Bernd Jendrissek <berndj@prism.co.za>
To: Kendrick Hamilton <hamilton@sedsystems.ca>
Cc: gcc@gcc.gnu.org, linux-kernel@vger.kernel.org
Subject: Re: Problem Installing Linux Kernel Module compiled with gcc-3.2.x
Message-ID: <20030530200206.B7564@prism.co.za>
References: <20030530192240.A7564@prism.co.za> <Pine.LNX.4.44.0305301128260.6111-100000@sw-55.sedsystems.ca>
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On Fri, May 30, 2003 at 11:31:57AM -0600, Kendrick Hamilton wrote:
> I have been manually recompillng the module and kernel to ensure they are 
> both compiled with the same version of gcc. When I do switch gcc versions, 
> I cp .config to config, make mrproper, cp config .config, make dep, make 
> all modules modules_install install; reboot; make clean on my driver the 
> make it.

Aargh.  Now if I had actually *read* your message I'd have picked that up.

Well, it's not maybe some *other* module that gets left behind in
/lib/modules/$VERSION?  No, that doesn't make too much sense.  That
doesn't gel with the crashes happening from the time you load *your*
module.

Uh, could it maybe be (gasp!) a *bug* in your module?  Maybe some
assumption your code is making is being invalidated by a new! improved!
optimization in GCC 3.x?  I know my module ha[ds] bugs...

Although... I must say that ever since I recompiled 2.4.18 with 3.2.x
(now 3.2.3), my machine seems somewhat less stable.  (I think) I *had* to
reboot yesterday after just 16 days' uptime after X or something else
with the keyboard went berserk.  But I'm not quite ready yet to "blame"
GCC for that.

>  On Fri, 30 May 2003, Bernd Jendrissek wrote:
> 
> > Not *exactly* on-topic for gcc@gcc.gnu.org I suppose, but here goes.
> > 
> > [Cc'ed to linux-kernel@vger.kernel.org]
> > 
> > On Fri, May 30, 2003 at 09:26:51AM -0600, Kendrick Hamilton wrote:
> > > 	I have a module for a custom developped PCI card. The device 
> > > driver is written for the Linux 2.4 series kernels. When I build the 
> > > module and the Linux kernel with gcc-2.95.3, the module installs 
> > > correctly. When I build the module and the Linux kernel with gcc-3.2.3 
> > > (also other gcc-3.2.x), the module installs but the Linux kernel crashes 
> > > in random places outside of the module. Do you have any suggestions of 
> > > what to look for? I can email you the complete module source code. I have 
> > > not tried gcc-3.3 because I cannot compile the current Linux kernel with 
> > > it (there is a known bug that is being fixed and should be out in 
> > > Linux-2.4.21).
> > 
> > Been there, done that, got the T-shirt.  I was lucky: while my module
> > installed, it broke in a fairly harmless way.  (It just didn't work; it
> > didn't screw with my system.)
> > 
> > If you look at linux/include/linux/spinlock.h, you'll see:
> > 
> > /*
> >  * Your basic spinlocks, allowing only a single CPU anywhere
> >  *
> >  * Most gcc versions have a nasty bug with empty initializers.
> >  */
> > #if (__GNUC__ > 2)
> >   typedef struct { } spinlock_t;
> >   #define SPIN_LOCK_UNLOCKED (spinlock_t) { }
> > #else
> >   typedef struct { int gcc_is_buggy; } spinlock_t;
> >   #define SPIN_LOCK_UNLOCKED (spinlock_t) { 0 }
> > #endif
> > 
> > There are a couple of spinlock_t's (directly or through other structs) in
> > the task_struct.  So when your module accesses parts of the "current"
> > task_struct beyond the first spinlock_t, you better hope it's reading and
> > not writing (which was the case with my module).
> > 
> > I bet your module modifies "current".
> > 
> > Hmm, actually I thought the kernel had a mechanism to prevent a GCC 3.x
> > module from being loaded into a GCC 2.x kernel and vice versa?
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