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Re: [PATCH 3/3] PowerPC: abort transaction in syscalls
- From: Will Schmidt <will_schmidt at vnet dot ibm dot com>
- To: Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Wed, 10 Dec 2014 14:20:26 -0600
- Subject: Re: [PATCH 3/3] PowerPC: abort transaction in syscalls
- Authentication-results: sourceware.org; auth=none
- References: <545CFDAE dot 1060401 at linux dot vnet dot ibm dot com> <54776136 dot 5010105 at linux dot vnet dot ibm dot com>
- Reply-to: will_schmidt at vnet dot ibm dot com
On Thu, 2014-11-27 at 15:36 -0200, Adhemerval Zanella wrote:
> On 07-11-2014 15:13, Adhemerval Zanella wrote:
> > 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.
A few cosmetics, and questions sprinkled throughout. No issues with
code functionality.
> >
> > To avoid side-effects being visible outside transactions, GLIBC with lock
> > elision enable issues a transaction abort instruction just before all
s/enable issues/enabled will issue/
> > syscalls if hardware supports hardware transactions.
> >
> > --
> >
> > * sysdeps/powerpc/nptl/tls.h (tcbhead_t): Add tm_capable field.
> > (TLS_INIT_TP): Add tm_capable initialization.
> > (TLS_DEFINE_INIT_TP): Likewise.
> > (THREAD_GET_TM_CAPABLE): New file: get tm_capable field value from
> > TCB.
> > (THREAD_SET_TM_CAPABLE): New file: set tm_capable field value in TCB.
> > * sysdeps/powerpc/nptl/tcb-offsets.sym (TM_CAPABLE): Add field offset
> > calculation.
> > * sysdeps/powerpc/powerpc32/sysdep.h (DO_CALL): Abort hardware
> > transactoion is lock elision is built and TCB tm_capable is set.
> > * sysdeps/powerpc/powerpc64/sysdep.h (DO_CALL): Likewise.
> > * sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h
> > (INTERNAL_SYSCALL_NCS): Likewise.
> > * sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h
> > (INTERNAL_SYSCALL_NCS): Likewise.
> > * sysdeps/powerpc/sysdep.h (ABORT_TRANSACTION): New define.
> >
> > ---
> >
> > diff --git a/sysdeps/powerpc/nptl/tcb-offsets.sym b/sysdeps/powerpc/nptl/tcb-offsets.sym
> > index f996759..d955142 100644
> > --- a/sysdeps/powerpc/nptl/tcb-offsets.sym
> > +++ b/sysdeps/powerpc/nptl/tcb-offsets.sym
> > @@ -19,6 +19,7 @@ POINTER_GUARD (offsetof (tcbhead_t, pointer_guard) - TLS_TCB_OFFSET - sizeof (
> > TAR_SAVE (offsetof (tcbhead_t, tar_save) - TLS_TCB_OFFSET - sizeof (tcbhead_t))
> > DSO_SLOT1 (offsetof (tcbhead_t, dso_slot1) - TLS_TCB_OFFSET - sizeof (tcbhead_t))
> > DSO_SLOT2 (offsetof (tcbhead_t, dso_slot2) - TLS_TCB_OFFSET - sizeof (tcbhead_t))
> > +TM_CAPABLE (offsetof (tcbhead_t, tm_capable) - TLS_TCB_OFFSET - sizeof (tcbhead_t))
> > #ifndef __ASSUME_PRIVATE_FUTEX
> > PRIVATE_FUTEX_OFFSET thread_offsetof (header.private_futex)
> > #endif
> > diff --git a/sysdeps/powerpc/nptl/tls.h b/sysdeps/powerpc/nptl/tls.h
> > index b80a5fb..37280d2 100644
> > --- a/sysdeps/powerpc/nptl/tls.h
> > +++ b/sysdeps/powerpc/nptl/tls.h
> > @@ -63,6 +63,8 @@ typedef union dtv
> > are private. */
> > typedef struct
> > {
> > + /* Indicate if hwcap2 has PPC_FEATURE2_HAS_HTM capability. */
> > + int tm_capable;
The comment here is possibly a bit verbose. This field doesn't need to
care where/or how we determine the value. How about just "Indicate if
HTM capable".
> > /* Reservation for Dynamic System Optimizer ABI. */
> > uintptr_t dso_slot2;
> > uintptr_t dso_slot1;
> > @@ -130,11 +132,17 @@ register void *__thread_register __asm__ ("r13");
> > special attention since 'errno' is not yet available and if the
> > operation can cause a failure 'errno' must not be touched. */
> > # define TLS_INIT_TP(tcbp) \
> > - (__thread_register = (void *) (tcbp) + TLS_TCB_OFFSET, NULL)
> > + ({ \
> > + __thread_register = (void *) (tcbp) + TLS_TCB_OFFSET; \
> > + THREAD_SET_TM_CAPABLE (GLRO (dl_hwcap2) & PPC_FEATURE2_HAS_HTM ? 1 : 0); \
> > + NULL; \
> > + })
> >
> > /* Value passed to 'clone' for initialization of the thread register. */
> > # define TLS_DEFINE_INIT_TP(tp, pd) \
> > - void *tp = (void *) (pd) + TLS_TCB_OFFSET + TLS_PRE_TCB_SIZE
> > + void *tp = (void *) (pd) + TLS_TCB_OFFSET + TLS_PRE_TCB_SIZE; \
> > + (((tcbhead_t *) ((char *) tp - TLS_TCB_OFFSET))[-1].tm_capable) = \
> > + THREAD_GET_TM_CAPABLE ();
> >
> > /* Return the address of the dtv for the current thread. */
> > # define THREAD_DTV() \
> > @@ -188,6 +196,13 @@ register void *__thread_register __asm__ ("r13");
> > + TLS_PRE_TCB_SIZE))[-1].pointer_guard \
> > = THREAD_GET_POINTER_GUARD())
> >
> > +/* tm_capable field in TCB head. */
> > +# define THREAD_GET_TM_CAPABLE() \
> > + (((tcbhead_t *) ((char *) __thread_register \
> > + - TLS_TCB_OFFSET))[-1].tm_capable)
> > +# define THREAD_SET_TM_CAPABLE(value) \
> > + (THREAD_GET_TM_CAPABLE () = (value))
> > +
> > /* l_tls_offset == 0 is perfectly valid on PPC, so we have to use some
> > different value to mean unset l_tls_offset. */
> > # define NO_TLS_OFFSET -1
Ok.
> > diff --git a/sysdeps/powerpc/powerpc32/sysdep.h b/sysdeps/powerpc/powerpc32/sysdep.h
> > index c8a56aa..c4b3ca8 100644
> > --- a/sysdeps/powerpc/powerpc32/sysdep.h
> > +++ b/sysdeps/powerpc/powerpc32/sysdep.h
> > @@ -88,7 +88,23 @@ GOT_LABEL: ; \
> > cfi_endproc; \
> > ASM_SIZE_DIRECTIVE(name)
> >
> > +#if !defined IS_IN_rtld && defined (ENABLE_LOCK_ELISION)
> > +# define ABORT_TRANSACTION \
> > + cmpwi 2,0; \
> > + beq 1f; \
> > + lwz 0,TM_CAPABLE(2); \
> > + cmpwi 0,0; \
> > + beq 1f; \
> > + li 0,_ABORT_SYSCALL; \
> > + tabort. 0; \
> > + .align 4; \
> > +1:
> > +#else
> > +# define ABORT_TRANSACTION
> > +#endif
> > +
> > #define DO_CALL(syscall) \
> > + ABORT_TRANSACTION \
> > li 0,syscall; \
> > sc
> >
> > diff --git a/sysdeps/powerpc/powerpc64/sysdep.h b/sysdeps/powerpc/powerpc64/sysdep.h
> > index b28fb9d..78722c6 100644
> > --- a/sysdeps/powerpc/powerpc64/sysdep.h
> > +++ b/sysdeps/powerpc/powerpc64/sysdep.h
> > @@ -283,7 +283,23 @@ LT_LABELSUFFIX(name,_name_end): ; \
> > TRACEBACK_MASK(name,mask) \
> > END_2(name)
> >
> > +#if !defined IS_IN_rtld && defined (ENABLE_LOCK_ELISION)
> > +# define ABORT_TRANSACTION \
> > + cmpdi 13,0; \
> > + beq 1f; \
> > + lwz 0,TM_CAPABLE(13); \
> > + cmpwi 0,0; \
> > + beq 1f; \
> > + li 0,_ABORT_SYSCALL; \
> > + tabort. 0; \
> > + .align 4; \
> > +1:
> > +#else
> > +# define ABORT_TRANSACTION
> > +#endif
> > +
> > #define DO_CALL(syscall) \
> > + ABORT_TRANSACTION \
> > li 0,syscall; \
> > sc
> >
> > diff --git a/sysdeps/powerpc/sysdep.h b/sysdeps/powerpc/sysdep.h
> > index e6627c0..c683066 100644
> > --- a/sysdeps/powerpc/sysdep.h
> > +++ b/sysdeps/powerpc/sysdep.h
> > @@ -21,6 +21,10 @@
> > */
> > #define _SYSDEPS_SYSDEP_H 1
> > #include <bits/hwcap.h>
> > +#ifdef ENABLE_LOCK_ELISION
> > +#include <tls.h>
> > +#include <htm.h>
> > +#endif
> >
> > #define PPC_FEATURE_970 (PPC_FEATURE_POWER4 + PPC_FEATURE_HAS_ALTIVEC)
> >
> > @@ -164,4 +168,21 @@
> > #define ALIGNARG(log2) log2
> > #define ASM_SIZE_DIRECTIVE(name) .size name,.-name
> >
> > +#else
> > +
> > +/* Linux kernel powerpc documentation states issuing a syscall inside a
> > + transaction is not recommended and may lead to undefined behavior. It
pointer to documentation?
> > + also states syscalls does not abort transactoin neither run in
transaction
'neither' is possibly out of place.
> > + transactional state. To avoid such traps, we abort transaction just
> > + before syscalls. */
> > +#if !defined IS_IN_rtld && defined (ENABLE_LOCK_ELISION)
> > +# define ABORT_TRANSACTION \
> > + ({ \
> > + if (THREAD_GET_TM_CAPABLE ()) \
> > + __builtin_tabort (_ABORT_SYSCALL); \
> > + })
> > +#else
> > +# define ABORT_TRANSACTION
> > +#endif
> > +
> > #endif /* __ASSEMBLER__ */
> > diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h b/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h
> > index 1a5e37a..0947ca3 100644
> > --- a/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h
> > +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h
> > @@ -194,6 +194,7 @@
> > register long int r11 __asm__ ("r11"); \
> > register long int r12 __asm__ ("r12"); \
> > LOADARGS_##nr(name, args); \
> > + ABORT_TRANSACTION; \
> > __asm__ __volatile__ \
> > ("sc \n\t" \
> > "mfcr %0" \
> > diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h b/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h
> > index 93e454e..a3cc302 100644
> > --- a/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h
> > +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h
> > @@ -201,6 +201,7 @@
> > register long int r7 __asm__ ("r7"); \
> > register long int r8 __asm__ ("r8"); \
> > LOADARGS_##nr (name, ##args); \
> > + ABORT_TRANSACTION; \
> > __asm__ __volatile__ \
> > ("sc\n\t" \
> > "mfcr %0\n\t" \
> >
> Ping.
>