On Mon, Sep 16, 2013 at 6:08 AM, Rusty Russell <ru...@rustcorp.com.au> wrote:
> Predates git, does anyone remember the rationale?
>
> ie:
> int test_bit(int nr, const volatile unsigned long *addr)
That's why we have full-history-linux ;-)
Unfortunately it doesn't show the rationale, as this change also predates
bitkeeper.
Since 2.1.30, volatile is used unconditionally:
commit 84d59b7dda1092a22663f4e2da77a6ce581b539e
Author: linus1 <torva...@linuxfoundation.org>
Date: Mon Mar 10 12:00:00 1997 -0600
Import 2.1.30
#ifdef __SMP__
#define LOCK_PREFIX "lock ; "
-#define SMPVOL volatile
#else
#define LOCK_PREFIX ""
-#define SMPVOL
#endif
/*
* This routine doesn't need to be atomic.
*/
-extern __inline__ int test_bit(int nr, const SMPVOL void * addr)
+extern __inline__ int __constant_test_bit(int nr, const volatile void * addr)
{
- return ((1UL << (nr & 31)) & (((const unsigned int *) addr)[nr >> 5])) !
+ return ((1UL << (nr & 31)) & (((const volatile unsigned int *) addr)[nr
}
+extern __inline__ int __test_bit(int nr, volatile void * addr)
+{
+ int oldbit;
+
+ __asm__ __volatile__(
+ "btl %2,%1\n\tsbbl %0,%0"
+ :"=r" (oldbit)
+ :"m" (ADDR),"ir" (nr));
+ return oldbit;
+}
+
+#define test_bit(nr,addr) \
+(__builtin_constant_p(nr) ? \
+ __constant_test_bit((nr),(addr)) : \
+ __test_bit((nr),(addr)))
+
/*
Between 1.3.75 and 2.1.30, volatile was used on SMP only:
commit 08c5b9d698e6ca2233aec0f7d7f0fdd6eb3ad235
Author: linus1 <torva...@linuxfoundation.org>
Date: Thu Mar 7 12:00:00 1996 -0600
Import 1.3.75
#ifdef __SMP__
#define LOCK_PREFIX "lock ; "
+#define SMPVOL volatile
#else
#define LOCK_PREFIX ""
+#define SMPVOL
#endif
/*
* This routine doesn't need to be atomic.
*/
-extern __inline__ int test_bit(int nr, const void * addr)
+extern __inline__ int test_bit(int nr, const SMPVOL void * addr)
{
return 1UL & (((const unsigned int *) addr)[nr >> 5] >> (nr & 31));
}
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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