__sync_lock_test_and_set on ARM

[Andrew Haley]

Segher Boessenkool writes:
 > As an aside...
 > 
 > > #define __KERNEL__
 > > #include <asm/atomic.h>
 > 
 > You don't want to do this, the stuff in the header files bracketed
 > with __KERNEL__ is for internal use in the Linux kernel only; with
 > newer kernel versions, that stuff isn't copied into the user headers
 > anymore even.

How annoying.

 > You can of course copy that code into your own code, or perhaps
 > glibc has similar functionality somewhere?

Well, this stuff really should be done by the compiler.  There is a
useful way to do compare and exchange that doesn't require knowledge
of hardware:

--------------------------------------------------------------------
typedef int (__kernel_cmpxchg_t)(int oldval, int newval, int *ptr);

#define __kernel_cmpxchg (*(__kernel_cmpxchg_t *)0xffff0fc0)

int n = 99;

int
main (void)
{
  __kernel_cmpxchg (99, 33, &n);
  return 0;
}
--------------------------------------------------------------------

This works on sufficiently recent ARM kernels, and on all ARM
hardware.

Andrew.


http://developer.osdl.org/dev/robustmutexes/REPOS/fusyn.hg/?cmd=file;filenode=3d1fa6de979c9ad079f9a103bf332d120dabe838;file=arch/arm/kernel/entry-armv.S