Re: [committed] hppa: Drop 16-byte pthread lock alignment

[Sam James <sam@gentoo.org>]

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John David Anglin <dave@parisc-linux.org> writes:

> [[PGP Signed Part:Undecided]]
> hppa: Drop 16-byte pthread lock alignment
>
> Linux threads were removed about 12 years ago and the current
> nptl implementation only requires 4-byte alignment for pthread
> locks.
>
> The 16-byte alignment causes various issues. For example in
> building ignition-msgs, we have:
>
> /usr/include/google/protobuf/map.h:124:37: error: static assertion failed
>   124 |   static_assert(alignof(value_type) <= 8, "");
>       |                 ~~~~~~~~~~~~~~~~~~~~^~~~
>
> This is caused by the 16-byte pthread lock alignment.

Dave will be aware of the context but posting this just for
completeness: see also: https://github.com/protocolbuffers/protobuf/issues/9433 where
David Seifert (soap@, CC'd) provided some analysis.

>
> Signed-off-by: John David Anglin <dave.anglin@bell.net>
> ---
>
> diff --git a/sysdeps/hppa/nptl/bits/pthreadtypes-arch.h b/sysdeps/hppa/nptl/bits/pthreadtypes-arch.h
> index 999195c5b0..c1a46d66d0 100644
> --- a/sysdeps/hppa/nptl/bits/pthreadtypes-arch.h
> +++ b/sysdeps/hppa/nptl/bits/pthreadtypes-arch.h
> @@ -40,7 +40,7 @@
>  #define __SIZEOF_PTHREAD_RWLOCK_T 64
>  #define __SIZEOF_PTHREAD_RWLOCKATTR_T 8
>  
> -#define __LOCK_ALIGNMENT __attribute__ ((__aligned__(16)))
> +#define __LOCK_ALIGNMENT
>  #define __ONCE_ALIGNMENT
>  
>  #endif	/* bits/pthreadtypes.h */
> diff --git a/sysdeps/hppa/nptl/bits/struct_rwlock.h b/sysdeps/hppa/nptl/bits/struct_rwlock.h
> index e83b4aab52..59bc9fe76f 100644
> --- a/sysdeps/hppa/nptl/bits/struct_rwlock.h
> +++ b/sysdeps/hppa/nptl/bits/struct_rwlock.h
> @@ -25,8 +25,14 @@ struct __pthread_rwlock_arch_t
>    /* In the old Linuxthreads pthread_rwlock_t, this is the
>       start of the 4-word 16-byte aligned lock structure. The
>       next four words are all set to 1 by the Linuxthreads
> -     PTHREAD_RWLOCK_INITIALIZER. We ignore them in NPTL.  */
> -  int __compat_padding[4] __attribute__ ((__aligned__(16)));
> +     PTHREAD_RWLOCK_INITIALIZER. We ignore them in NPTL.
> +
> +     The 16-byte aligned lock stucture causes various pthread
> +     structures to be over aligned. This causes some builds
> +     to fail which assume a maximum alignment of 8 bytes.
> +     Linuxthreads has been removed for 12 years, so drop
> +     alignment of lock structure.  */
> +  int __compat_padding[4];
>    unsigned int __readers;
>    unsigned int __writers;
>    unsigned int __wrphase_futex;
>
> [[End of PGP Signed Part]]


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