[PATCH] Memory fencing problem in pthread cancellation

[Jeff Law]

On 01/14/2013 03:11 PM, Carlos O'Donell wrote:
> On 01/14/2013 03:24 PM, Jeff Law wrote:
>
>
> You need to fix the assembly also.
[ ... ]

>
> Thus you need something like this completely untested patch:
>
> diff --git a/ports/sysdeps/arm/bits/atomic.h b/ports/sysdeps/arm/bits/atomic.h
> index 6e20df7..b0f45ad 100644
> --- a/ports/sysdeps/arm/bits/atomic.h
> +++ b/ports/sysdeps/arm/bits/atomic.h
> @@ -42,6 +42,7 @@ void __arm_link_error (void);
>   # define atomic_full_barrier() __sync_synchronize ()
>   #else
>   # define atomic_full_barrier() __arm_assisted_full_barrier ()
> +# define atomic_asm_full_barrier() __arm_asm_assisted_full_barrier ()
>   #endif
Added.

>
>   /* An OS-specific bits/atomic.h file will define this macro if
> diff --git a/ports/sysdeps/unix/sysv/linux/arm/bits/atomic.h b/ports/sysdeps/unix/sysv/linux/arm/bits/atomic.h
> index c76b8f3..726d3ce 100644
> --- a/ports/sysdeps/unix/sysv/linux/arm/bits/atomic.h
> +++ b/ports/sysdeps/unix/sysv/linux/arm/bits/atomic.h
> @@ -17,7 +17,8 @@
>      <http://www.gnu.org/licenses/>.  */
>
>   /* If the compiler doesn't provide a primitive, we'll use this macro
> -   to get assistance from the kernel.  */
> +   to get assistance from the kernel. This should call the
> +   __kuser_memory_barrier helper in the kernel.  */
>   #ifdef __thumb2__
>   # define __arm_assisted_full_barrier() \
>        __asm__ __volatile__                                                    \
> @@ -25,6 +26,11 @@
>                "movt\tip, #0xffff\n\t"                                         \
>                "blx\tip"                                                       \
>                : : : "ip", "lr", "cc", "memory");
> +/* The asm variant is used as an insert into existing asm statements.  */
> +# define __arm_asm_assisted_full_barrier() \
> +       "       movw    ip, #0x0fa0\n" \
> +       "       movt    ip, #0xffff\n" \
> +       "       blx     ip"
>   #else
>   # define __arm_assisted_full_barrier() \
>        __asm__ __volatile__                                                    \
> @@ -32,6 +38,11 @@
>                "mov\tlr, pc\n\t"                                               \
>                "add\tpc, ip, #(0xffff0fa0 - 0xffff0fff)"                       \
>                : : : "ip", "lr", "cc", "memory");
> +/* The asm variant is used as an insert into existing asm statements.  */
> +# define __arm_asm_assisted_full_barrier() \
> +       "       mov     ip, #0xffff0fff\n" \
> +       "       mov     lr, pc\n" \
> +       "       add     pc, ip, #(0xffff0fa0 - 0xffff0fff)"
>   #endif
Added.


>
>   /* Atomic compare and exchange.  This sequence relies on the kernel to
> diff --git a/ports/sysdeps/unix/sysv/linux/arm/nptl/unwind-forcedunwind.c b/ports/sysdeps/unix/sysv/linux/arm/nptl/unwind-forcedunwind.c
> index 58ca9ac..d7ac847 100644
> --- a/ports/sysdeps/unix/sysv/linux/arm/nptl/unwind-forcedunwind.c
> +++ b/ports/sysdeps/unix/sysv/linux/arm/nptl/unwind-forcedunwind.c
> @@ -104,6 +104,7 @@ asm (
>   "      mov     r6, r0\n"
>   "      cmp     r3, #0\n"
>   "      beq     4f\n"
> +       atomic_asm_full_barrier()
>   "5:    mov     r0, r6\n"
>   "      ldmfd   sp!, {r4, r5, r6, lr}\n"
>   "      " CFI_ADJUST_CFA_OFFSET (-16) "\n"
> @@ -123,7 +124,7 @@ asm (
>   #else
>   "1:    .word   _GLOBAL_OFFSET_TABLE_ - 3b - 8\n"
>   #endif
> -"2:    .word   libgcc_s_resume(GOTOFF)\n"
> +"2:    .word   libgcc_s_handle(GOTOFF)\n"
>   "      .size   _Unwind_Resume, .-_Unwind_Resume\n"
>   );
Not added as there's a later revision.

jeff