[GHC] #10244: "memory barriers unimplemented on this architecture" on ARM pre-ARMv7

[GHC]

#10244: "memory barriers unimplemented on this architecture" on ARM pre-ARMv7
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        Reporter:  rwbarton          |                   Owner:  simonmar
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:  7.10.2
       Component:  Runtime System    |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:  arm
 Type of failure:  Building GHC      |               Test Case:
  failed                             |                Blocking:
      Blocked By:                    |  Differential Revisions:
 Related Tickets:                    |
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Changes (by slyfox):

 * cc: slyfox (added)


Comment:

 Do you have a particular build error? I wonder what else
 is visible there.

 From what I see in the '''includes/stg/SMP.h''' it's just omission
 in implementation.

 There is properly-looking '''write_barrier'''
 {{{
 EXTERN_INLINE void
 write_barrier(void) {
 ...
 #elif arm_HOST_ARCH && defined(arm_HOST_ARCH_PRE_ARMv7)
     __asm__ __volatile__ ("" : : : "memory");
 #elif (arm_HOST_ARCH && !defined(arm_HOST_ARCH_PRE_ARMv7)) ||
 aarch64_HOST_ARCH
     __asm__ __volatile__ ("dmb  st" : : : "memory");
 ...
 }}}
 but not load_load:
 {{{
 EXTERN_INLINE void
 load_load_barrier(void) {
 ...
 #elif arm_HOST_ARCH && !defined(arm_HOST_ARCH_PRE_ARMv7)
 __asm__ __volatile__ ("dmb" : : : "memory");
 ...
 }}}

 I think stubbing out with
 {{{
 __asm__ __volatile__ ("" : : : "memory");
 }}}
 is best we can do there.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10244#comment:2>
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