Re: Problem Installing Linux Kernel Module compiled with gcc-3.2.x

[Joe Buck <jbuck at synopsys dot com>]

On Fri, May 30, 2003 at 07:22:40PM +0200, Bernd Jendrissek wrote:

> 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

Yuk!  What is the benefit of introducing this incompatibility?  #ifdefs
are harmful to maintainance, and it's only one word, so why not always
put in the dummy struct member?

> 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?

Is there any reason, other than the above-described bit of evil, for doing
this (forbidding mixing)?  It prevents the bug-finding approach I
described earlier (a binary search for finding miscompiled code) from
working.