Work around a GCC behavior with hardware transactional memory built-ins.
GCC doesn't treat the PowerPC transactional built-ins as compiler
barriers, moving instructions past the transaction boundaries and
altering their atomicity.
This patch adds a new feature for powerpc. In order to get faster access to
the HWCAP/HWCAP2 bits and platform number (i.e. for implementing
__builtin_cpu_is () / __builtin_cpu_supports () in GCC) without the overhead of
reading from the auxiliary vector, we now reserve space for them in the TCB.
This is an ABI change for GLIBC 2.23.
A new versioned symbol '__parse_hwcap_and_convert_at_platform' is available to
get the data from the auxiliary vector and parse it, and store it for later use
in the TLS initialization code. This function is called very early
(in _dl_sysdep_start () via DL_PLATFORM_INFO for the dynamic linking case, and
in __libc_start_main () for the static linking case) to make sure the data is
available at the time of TLS initialization.
* sysdeps/powerpc/Makefile (sysdep-dl-routines): Add hwcapinfo.
(sysdep_routines): Likewise.
(sysdep-rtld-routines): Likewise.
[$(subdir) = nptl](tests): Add test-get_hwcap and test-get_hwcap-static
[$(subdir) = nptl](tests-static): test-get_hwcap-static
* sysdeps/powerpc/Versions: Added new
__parse_hwcap_and_convert_at_platform symbol to GLIBC-2.23.
* sysdeps/powerpc/hwcapinfo.c: New file.
(__tcb_parse_hwcap_and_convert_at_platform): New function to initialize
and parse hwcap, hwcap2 and platform number information.
* sysdeps/powerpc/hwcapinfo.h: New file. Creates global variables
to store HWCAP+HWCAP2 and platform number.
* sysdeps/powerpc/nptl/tcb-offsets.sym: Added new offsets
for HWCAP+HWCAP2 and platform number in the TCB.
* sysdeps/powerpc/nptl/tls.h: New functionality. Stores
the HWCAP, HWCAP2 and platform number in the TCB.
(dtv): Added new fields for HWCAP+HWCAP2 and platform number.
(TLS_INIT_TP): Included calls to add the hwcap and
at_platform values in the TCB in TP initialization.
(TLS_DEFINE_INIT_TP): Likewise.
(THREAD_GET_HWCAP): New macro.
(THREAD_SET_HWCAP): Likewise.
(THREAD_GET_AT_PLATFORM): Likewise.
(THREAD_SET_AT_PLATFORM): Likewise.
* sysdeps/powerpc/powerpc32/dl-machine.h:
(dl_platform_init): New function that calls
__parse_hwcap_and_convert_at_platform for the dymanic linking case for
powerpc32.
* sysdeps/powerpc/powerpc64/dl-machine.h: Likewise, for powerpc64.
* sysdeps/powerpc/test-get_hwcap-static.c: New file. Testcase for
this functionality, static linking case.
* sysdeps/powerpc/test-get_hwcap.c: New file. Likewise, dynamic
linking case.
* sysdeps/unix/sysv/linux/powerpc/libc-start.c: Added call to
__parse_hwcap_and_convert_at_platform for the static linking case.
* sysdeps/unix/sysv/linux/powerpc/powerpc32/ld.abilist:
Included the new __parse_hwcap_and_convert_at_platform symbol in the
ABI list for GLIBC 2.23.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/ld-le.abilist:
Likewise.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/ld.abilist:
Likewise.
This patch optimizes powerpc spinlock implementation by:
* Use the correct EH hint bit on the larx for supported ISA. For lock
acquisition, the thread that acquired the lock with a successful stcx
does not want to give away the write ownership on the cacheline. The
idea is to make the load reservation "sticky" about retaining write
authority to the line. That way, the store that must inevitably come
to release the lock can succeed quickly and not contend with other
threads issuing lwarx. If another thread does a store to the line
(false sharing), the winning thread must give up write authority to
the proper value of EH for the larx for a lock acquisition is 1.
* Increase contented lock performance by up to 40%, and no measurable
impact on uncontended locks on P8.
Thanks to Adhemerval Zanella who did most of the work. I've run some
tests, and addressed some minor feedback.
* sysdeps/powerpc/nptl/pthread_spin_lock.c (pthread_spin_lock):
Add lwarx hint, and use macro for acquire instruction.
* sysdeps/powerpc/nptl/pthread_spin_trylock.c (pthread_spin_trylock):
Likewise.
* sysdep/unix/sysv/linux/powerpc/pthread_spin_unlock.c: Move to ...
* sysdeps/powerpc/nptl/pthread_spin_unlock.c: ... here, and
update to use new atomic macros.
The skip_lock_out_of_tbegin_retries adaptive parameter was
not being used correctly, nor as described. This prevents
a fallback for all users of the lock if a transient abort
occurs within the accepted number of retries.
[BZ #19174]
* sysdeps/powerpc/nptl/elide.h (__elide_lock): Fix usage of
.skip_lock_out_of_tbegin_retries.
* sysdeps/unix/sysv/linux/powerpc/elision-lock.c
(__lll_lock_elision): Likewise, and respect a value of
try_tbegin <= 0.
The previous code used to evaluate the preprocessor token is_lock_free to
a variable before starting a transaction. This behavior can cause an
error if another thread got the lock (without using a transaction)
between the evaluation of the token and the beginning of the transaction.
This bug can be triggered with the following order of events:
1. The lock accessed by is_lock_free is free.
2. Thread T1 evaluates is_lock_free and stores into register R1 that the
lock is free.
3. Thread T2 acquires the same lock used in is_lock_free.
4. T1 begins the transaction, creating a memory barrier where is_lock_free
is false, but R1 is true.
5. T1 reads R1 and doesn't abort the transaction.
6. T1 calls ELIDE_UNLOCK, which reads false from is_lock_free and decides
to unlock a lock acquired by T2, leading to undefined behavior.
This patch delays the evaluation of is_lock_free to inside a transaction
by moving this part of the code to the macro ELIDE_LOCK.
[BZ #18743]
* sysdeps/powerpc/nptl/elide.h (__elide_lock): Move most of this
code to...
(ELIDE_LOCK): ...here.
(__get_new_count): New function with part of the code from
__elide_lock that updates the value of adapt_count after a
transaction abort.
(__elided_trylock): Moved this code to...
(ELIDE_TRYLOCK): ...here.
Linux kernel powerpc documentation states issuing a syscall inside a
transaction is not recommended and may lead to undefined behavior. It
also states syscalls does not abort transactoin neither they run in
transactional state.
To avoid side-effects being visible outside transactions, GLIBC with
lock elision enabled will issue a transaction abort instruction just
before all syscalls if hardware supports hardware transactions.
This patch adds support for lock elision using ISA 2.07 hardware
transactional memory for rwlocks. The logic is similar to the
one presented in pthread_mutex lock elision.
This patch makes files using __ASSUME_* macros include
<kernel-features.h> explicitly, rather than relying on some other
header (such as tls.h, lowlevellock.h or pthreadP.h) to include it
implicitly. (I omitted cases where I've already posted or am testing
the patch that stops the file from needing __ASSUME_* at all.) This
accords with the general principle of making source files include the
headers for anything they use, and also helps make it safe to remove
<kernel-features.h> includes from any file that doesn't use
__ASSUME_* (some of those may be stray includes left behind after
increasing the minimum kernel version, others may never have been
needed or may have become obsolete after some other change).
Tested x86_64 that the disassembly of installed shared libraries is
unchanged by this patch.
* nptl/pthread_cond_wait.c: Include <kernel-features.h>.
* nptl/pthread_rwlock_timedrdlock.c: Likewise.
* nptl/pthread_rwlock_timedwrlock.c: Likewise.
* nptl/sysdeps/unix/sysv/linux/lowlevelrobustlock.c: Likewise.
* nscd/nscd.c: Likewise.
* sysdeps/i386/nptl/tcb-offsets.sym: Likewise.
* sysdeps/powerpc/nptl/tcb-offsets.sym: Likewise.
* sysdeps/sh/nptl/tcb-offsets.sym: Likewise.
* sysdeps/x86_64/nptl/tcb-offsets.sym: Likewise.
