[parisc-linux] 2.4.20-pa27 64bits smp problem!

[Joel Soete]

>> Sorry Dave I do not find this stuff.
>
>The place to look is
>
>linuxthreads/sysdeps/unix/sysv/linux/hppa/bits/initspin.h.
>
>It is rather buried.  Carlos and I have had some rather lengthy
>discussions on how to implement pthread locking in glibc given
>the limitations in aligning data on the stack and also for data
>allocated by malloc.  This might be relevant to the kernel
>locking code.
>
>>  #define rwlock_init(lp)	do { *(lp) = RW_LOCK_UNLOCKED; } while (0)
>
>The above macro uses a compound literal.  This creates a unique object
>in the scope in which the macro is used.  As this is a BLKmode object,
>the alignment of the object is set to GCC's definition for BIGGEST_ALIGNMENT.
>The overall alignment also won't be better than STACK_BOUNDARY.  It
>is possible to use a "static" macro argument in which case space for the
>object will be allocated in the .bss section rather than on the stack.
>This also allows the alignment attribute to work.  If you do this, then
>you have to worry about whether the code needs to be reentrant.
>
>On the hppa64 port (3.3 & later), BIGGEST_ALIGNMENT, STACK_BOUNDARY
>and PREFERRED_STACK_BOUNDARY are now all 128 bits.  Prior to 3.3,
>PREFERRED_STACK_BOUNDARY is 1024 bits but this is wrong.  The runtime
>documentation specifies 128 bits (16 bytes) for the stack alignment
>on the 64-bit port.  Using a larger boundary just wastes space.
>Stack alignment is also determined by what you start with.
>
>Also note, any attempt to provide an overall alignment for the compound
>literal on the stack is ignored.  However, as all 64-bit machines are
>PA 2.0, this doesn't matter.  On the otherhand, the alignment does
>matter for the 32-bit port on PA 1.1 machines.  There the ldcw insn
>has to operate on 16-byte aligned data.  GCC from the master source
>has BIGGEST_ALIGNMENT set to 64-bits on the 32-bit port.  So, the
>above macro won't create a properly aligned lock.  Debian 3.0.4 has
>BIGGEST_ALIGNMENT set to 128, so it should be used for PA 1.1 kernel
>builds until this issue is resolved.
>
Thanks for all info ;)

>> Any better idea?
>
>Not really.  I might use a name like SPIN_LOCK_UNLOCKED_INIT rather than
>C_SPIN_LOCK_UNLOCKED, as I think it is slightly more descriptive.
>
Ok for me (my C_ would stand for Constant form)

Joel


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