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Diffstat (limited to 'REORG.TODO/sysdeps/unix/sysv/linux/hppa/internaltypes.h')
| -rw-r--r-- | REORG.TODO/sysdeps/unix/sysv/linux/hppa/internaltypes.h | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/REORG.TODO/sysdeps/unix/sysv/linux/hppa/internaltypes.h b/REORG.TODO/sysdeps/unix/sysv/linux/hppa/internaltypes.h new file mode 100644 index 0000000000..d6496579da --- /dev/null +++ b/REORG.TODO/sysdeps/unix/sysv/linux/hppa/internaltypes.h @@ -0,0 +1,84 @@ +#include_next <internaltypes.h> +#ifndef _INTERNAL_TYPES_H_HPPA_ +#define _INTERNAL_TYPES_H_HPPA_ 1 +#include <atomic.h> + +/* In GLIBC 2.10 HPPA switched from Linuxthreads to NPTL, and in order +to maintain ABI compatibility with pthread_cond_t, some care had to be +taken. + +The NPTL pthread_cond_t grew in size. When HPPA switched to NPTL, we +dropped the use of ldcw, and switched to the kernel helper routine for +compare-and-swap. This allowed HPPA to use the 4-word 16-byte aligned +lock words, and alignment words to store the additional pthread_cond_t +data. Once organized properly the new NPTL pthread_cond_t was 1 word +smaller than the Linuxthreads version. + +However, we were faced with the case that users may have initialized the +pthread_cond_t with PTHREAD_COND_INITIALIZER. In this case, the first +four words were set to one, and must be cleared before any NPTL code +used these words. + +We didn't want to use LDCW, because it continues to be a source of bugs +when applications memset pthread_cond_t to all zeroes by accident. This +works on all other architectures where lock words are unlocked at zero. +Remember that because of the semantics of LDCW, a locked word is set to +zero, and an unlocked word is set to 1. + +Instead we used atomic_compare_and_exchange_val_acq, but we couldn't use +this on any of the pthread_cond_t words, otherwise it might interfere +with the current operation of the structure. To solve this problem we +used the left over word. + +If the stucture was initialized by a legacy Linuxthread +PTHREAD_COND_INITIALIZER it contained a 1, and this indicates that the +structure requires zeroing for NPTL. The first thread to come upon a +pthread_cond_t with a 1 in the __initializer field, will +compare-and-swap the value, placing a 2 there which will cause all other +threads using the same pthread_cond_t to wait for the completion of the +initialization. Lastly, we use a store (with memory barrier) to change +__initializer from 2 to 0. Note that the store is strongly ordered, but +we use the PA 1.1 compatible form which is ",ma" with zero offset. + +In the future, when the application is recompiled with NPTL +PTHREAD_COND_INITIALIZER it will be a quick compare-and-swap, which +fails because __initializer is zero, and the structure will be used as +is correctly. */ + +#define cond_compat_clear(var) \ +({ \ + int tmp = 0; \ + var->__data.__wseq = 0; \ + var->__data.__signals_sent = 0; \ + var->__data.__confirmed = 0; \ + var->__data.__generation = 0; \ + var->__data.__mutex = NULL; \ + var->__data.__quiescence_waiters = 0; \ + var->__data.__clockid = 0; \ + /* Clear __initializer last, to indicate initialization is done. */ \ + /* This synchronizes-with the acquire load below. */ \ + atomic_store_release (&var->__data.__initializer, 0); \ +}) + +#define cond_compat_check_and_clear(var) \ +({ \ + int v; \ + int *value = &var->__data.__initializer; \ + /* This synchronizes-with the release store above. */ \ + while ((v = atomic_load_acquire (value)) != 0) \ + { \ + if (v == 1 \ + /* Relaxed MO is fine; it only matters who's first. */ \ + && atomic_compare_exchange_acquire_weak_relaxed (value, 1, 2)) \ + { \ + /* We're first; initialize structure. */ \ + cond_compat_clear (var); \ + break; \ + } \ + else \ + /* Yield before we re-check initialization status. */ \ + sched_yield (); \ + } \ +}) + +#endif |