Re: NPTL for hppa-linux is not backwards compatible with Linuxthreads.

On 2/18/07, Roland McGrath <[email protected]> wrote:
> > NPTL for hppa-linux is not backwards compatible with Linuxthreads, we
> > have broken the pthread ABI.
>
> Please elaborate on exactly which types and entrypoints are incompatible.

All statically initialized locks are broken. We made locks smaller,
and changed the value of the static initialization.

e.g.
pthread_mutex_t smutex = PTHREAD_MUTEX_INITIALIZER;

Linuxthreads:
smutex.__m_lock == {1,1,1,1}

NPTL:
smutex.__m_lock == 0

On Linuxthreads hppa-linux used a  four word structure to represent a
lock. We used a structure to get a runtime 16-byte aligned lock word
to meet the requirements of the hardware "load and clear word." Since
the only available atomic hardware instruction is "load and clear
word", a lock is locked with a value of one, and unlocked with a value
of zero.

For NPTL we created a "compare and exchange" light-weight kernel
syscall. The light-weight kernel syscall is the basis for
atomic_compare_and_exchange_val_acq(). All other primitives are built
on this primitive. In this implementation we can use a single word
lock, like all other architectures, and our lowlevellock.h/.c
implementations are virtually identical to other architectures.

Any comments?

Cheers,
Carlos.