---
- branch: MAIN
  date: Sat Apr  9 12:06:48 UTC 2022
  files:
  - new: '1.7'
    old: '1.6'
    path: src/common/lib/libc/arch/sparc64/atomic/membar_ops.S
    pathrev: src/common/lib/libc/arch/sparc64/atomic/membar_ops.S@1.7
    type: modified
  id: 20220409T120648Z.e4eb7141ed3e3c42a0e9d8596d191860853e35e5
  log: |
    sparc64: Fix membar_sync by issuing membar #StoreLoad.

    In TSO this is the only memory barrier ever needed, and somehow we
    got this wrong and instead issued an unnecessary membar #LoadLoad --
    not needed even in PSO let alone in TSO.

    XXX Apparently we may run userland programs with PSO or RMO, in which
    case all of these membars need fixing:

                            PSO                     RMO
    membar_consumer         nop                     membar #LoadLoad
    membar_producer         membar #StoreStore      membar #StoreStore
    membar_enter            nop                     membar #LoadLoad|LoadStore
    membar_exit             membar #StoreStore      membar #LoadStore|StoreStore
    membar_sync             membar #StoreLoad|StoreStore
                                                    membar #...everything...

    But at least this fixes the TSO case in which we run the kernel.
    Also I'm not sure there's any non-TSO hardware out there in practice.
  module: src
  subject: 'CVS commit: src/common/lib/libc/arch/sparc64/atomic'
  unixtime: '1649506008'
  user: riastradh