[parisc-linux] ldcw in __pthread_acquire

[Alan Modra]

On Fri, 15 Dec 2000, John Marvin wrote:

> 
> I just ran into an unaligned data reference in user land.  The problem is
> that the routine __pthread_acquire (in libpthread) does a ldcw, but it is
> not ensuring that the address it is operating on is 16 byte aligned (it is
> operating on the address that was passed in as the first argument).  Some
> processors don't require the 16 byte alignment, but many do.
> 
> I haven't looked at the source (I just found the location by disassembly),
> so I don't know what the root cause is.  The actual ldcw is probably from
> an inlined function or macro, e.g. spin_lock().  My first guess would be
> that it is using the machine dependent spin_lock macro, but the procedure
> which called __pthread_acquire is passing in a structure whose lock field
> does not have the aligned(16) attribute.
> 
> I don't have time to look at this right now.  Any volunteers?

This isn't exactly volunteering, but I've looked at this code before.
Here's where the problem is:

glibc/linuxthreads/sysdeps/pthread/bits/pthreadtypes.h

struct _pthread_fastlock
{
  long int __status;   /* "Free" or "taken" or head of waiting list */
  int __spinlock;      /* Used by compare_and_swap emulation. Also,
			  adaptive SMP lock stores spin count here. */
};

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