Messages in this thread Patch in this message |  | | | Date | Fri, 30 May 2003 20:43:32 +0200 | | From | Bernd Jendrissek <> | | Subject | Re: Problem Installing Linux Kernel Module compiled with gcc-3.2.x |
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On Fri, May 30, 2003 at 10:33:29AM -0700, Joe Buck wrote: > 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?
I dont speak for the kernel people, but...
I suppose some people just insist on squeezing every last cycle out of their machines. For my home PC (a 486 with 5MB RAM running linux 2.0.30), I am quite grateful for such cycle and bit saving. Believe me, I notice whether I have apache running or not. :)
Hmm, yes, it does seem to be just one word. grep -r spinlock_t . |wc -l says 1013 here, that's across *all* architectures. IOW 4052 bytes - that's *one page* - on i386! Never mind what definition tcc will give to __GNUC__
So there I thought I was going to justify the kernel. Instead I mostly agree with Joe! I'm also sure there have been flamewars about this...
> > 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.
Between GCC 2.x and 3.x the *major* version changed (duh). I would imagine that people are/were (justifiably?) concerned that ABI's might have changed. From your response, I assume there are no ABI changes for C at least? I suppose a gratuitous ABI change would constitute a bug, though...
BTW I said "I thought" - it appears there is in fact no such mechanism.
Okay, so here's a PR (Public Relations, not Problem Report) patch just for you, Joe: <with a fistful of smileys :)>
(It also gets rid of some of that crazy 2-space indentation.)
diff -u linux/include/linux/spinlock.h.borig linux/include/linux/spinlock.h --- linux/include/linux/spinlock.h.borig Tue May 13 17:05:57 2003 +++ linux/include/linux/spinlock.h Fri May 30 20:29:42 2003 @@ -53,13 +53,8 @@ * * 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 +typedef struct { int gcc_was_buggy; } spinlock_t; +#define SPIN_LOCK_UNLOCKED (spinlock_t) { 0 } #define spin_lock_init(lock) do { } while(0) #define spin_lock(lock) (void)(lock) /* Not "unused variable". */ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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