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    • Tom Lane's avatar
      Provide a way to control SysV shmem attach address in EXEC_BACKEND builds. · a74740fb
      Tom Lane authored
      In standard non-Windows builds, there's no particular reason to care what
      address the kernel chooses to map the shared memory segment at.  However,
      when building with EXEC_BACKEND, there's a risk that the chosen address
      won't be available in all child processes.  Linux with ASLR enabled (which
      it is by default) seems particularly at risk because it puts shmem segments
      into the same area where it maps shared libraries.  We can work around
      that by specifying a mapping address that's outside the range where
      shared libraries could get mapped.  On x86_64 Linux, 0x7e0000000000
      seems to work well.
      
      This is only meant for testing/debugging purposes, so it doesn't seem
      necessary to go as far as providing a GUC (or any user-visible
      documentation, though we might change that later).  Instead, it's just
      controlled by setting an environment variable PG_SHMEM_ADDR to the
      desired attach address.
      
      Back-patch to all supported branches, since the point here is to
      remove intermittent buildfarm failures on EXEC_BACKEND animals.
      Owners of affected animals will need to add a suitable setting of
      PG_SHMEM_ADDR to their build_env configuration.
      
      Discussion: https://postgr.es/m/7036.1492231361@sss.pgh.pa.us
      a74740fb
    • Tom Lane's avatar
      Fix erroneous cross-reference in comment. · bfba563b
      Tom Lane authored
      Seems to have been introduced in commit c219d9b0.  I think there indeed
      was a "tupbasics.h" in some early drafts of that refactoring, but it
      didn't survive into the committed version.
      
      Amit Kapila
      bfba563b
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