Messages in this thread | | | Date | Mon, 9 Oct 2006 01:36:17 +0200 | From | Willy Tarreau <> | Subject | Re: 2.4.x: i386/x86_64 bitops clobberings |
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On Mon, Oct 09, 2006 at 12:53:56AM +0200, Jan Kiszka wrote: > Willy Tarreau wrote: > > Hi Jan, > > > > On Sun, Oct 08, 2006 at 11:42:07PM +0200, Jan Kiszka wrote: > >> Hi, > >> > >> after going through debugging hell with some out-of-tree code, I > >> realised that this patch > >> > >> http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=92934bcbf96bc9dc931c40ca5f1a57685b7b813b > >> > >> makes a difference: current 2.6 works with the following code sequence > >> as expected (printk is executed), 2.4 fails. > >> > >> > >> #include <asm/bitops.h> > >> #include <linux/module.h> > >> > >> unsigned long a = 1; > >> > >> int module_init(void) > >> { > >> unsigned long b = 0; > >> int x; > >> > >> x = __test_and_set_bit(0, &b); > >> if (__test_and_set_bit(0, &a)) > >> printk("x = %d\n", x); > >> > >> return -1; > >> } > >> > >> > >> There will likely be a way to work around my issue. Nevertheless, I > >> wondered if that patch was already considered for 2.4 inclusion. Or is > >> there no risk that in-tree code is affected? > > > > While I remember some discussion on the subject for 2.6, I don't > > recall anything similiar in 2.4. Wouldn't you happen to build with > > gcc-3.4 ? IIRC, the clobbering changed around this version. Could > > I used gcc 3.3.6-13 (Debian).
OK, fine.
> > you confirm that the patch you pointed above fixes the problem for > > your case ? > > Yes. I ported the x86 part back to 2.4.33 and my problem disappeared.
I've done it too, but unfortunately, I discovered that it does not build with gcc-2.95 anymore, while 3.3 is fine :
cyclades.c: In function `cyy_interrupt': /usr/src/git/linux-2.4/include/asm/bitops.h:130: inconsistent operand constraints in an `asm' cyclades.c: In function `cyz_handle_rx': /usr/src/git/linux-2.4/include/asm/bitops.h:130: inconsistent operand constraints in an `asm'
127 __asm__ __volatile__( LOCK_PREFIX 128 "btsl %2,%1\n\tsbbl %0,%0" 129 :"=r" (oldbit),"+m" (ADDR) 130 :"Ir" (nr) : "memory");
I don't know what the right solution should be. I'm not fond of #ifdefs, and I'm embarrassed to know that gcc can do all sorts of nasty things due to a wrong clobbering :-/
If you have any idea on the subject, I'm willing to try.
Regards, Willy
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