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Problem Report 1493 Details

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Report 1493 Actions

    Problem Report Number 1493
    Submitter's Classification Test Suite problem
    State Resolved
    Resolution Test Suite Deficiency (TSD)
    Problem Resolution ID TSD.X.0775
    Raised 1970-01-01 08:00
    Updated 2003-03-13 08:00
    Published 1995-08-25 08:00
    Product Standard Internationalised System Calls and Libraries Extended (UNIX 95)
    Certification Program The Open Brand certification program
    Test Suite VSU version 4.0.2
    Test Identification fmmap/mmap 3
    Problem Summary TSD4U.00038 Test mandates mapping with PROT_EXEC for writable files, spec does not require this.
    Problem Text
    This test calls a library routine, create_exex_file() with
    "O_RDWR" flag and then call mmap() to map in the file with
    "PROT_EXEC" flag. Because HP's implementation does not
    allow mapping a file for execution when the file is currently
    open for writing. The mmap() call fails with errno set to
    ETXTBSY. HP's implementation does not violate the standards
    since no such condition is described on the CASPEC pages. So
    HP filed a waiver request classifying this as a test error.
    The request was rejected and the response was:

    > Our opinion differs.
    > Although we can find nothing in the spec to forbid the behavior
    > you describe, we believe the intent was to support PROT_ALL
    > in a MAP_SHARED environment (this being necessary to allow
    > an efficient means of producing self modifying code).
    > We believe LISP vendors in particular will depend on this.
    > With this in mind, we are reluctant to change the test without
    > further direction from X/Open.
    > If you would like to pursue this further we suggest you file
    > an interpretation request with X/Open. If they rule in your
    > favor we will be happy to align the test with their decision.

    We do not agree with the response. UNIX has NEVER allowed to
    open an executable file for write while it is being executed.
    The case cited regarding LISP is also not true. LISP switches
    data memory to executable memory and back again but NEVER
    expects to be able to write in to the memory while it is
    executing. This limitation is common architectural requirement
    on most, if not all computer architectures.

    Lastly, as the response stated, the spec does not restrict the
    behavior described and as such no conformance distinction should
    be made based upon unspecified behavior in the spec.
    Test Output
    SECTION: Discrete Tests

    TEST CASE: mmap

    TEST PURPOSE #3
    A successful call to void *mmap(void *addr, size_t
    len, int prot, int flags, int fildes, off_t off) when
    fildes is associated with a regular file, the
    MAP_SHARED flag is set in flags, and the PROT_EXEC
    flag is set in prot shall map len bytes at offset off
    in the memory object represented by fildes into the
    address space of the process, allow the mapped area to
    be executed, and return the location in the address
    space at which the mapping is made.
    PREP: Obtain the system page size by call to
    sysconf(_SC_PAGESIZE)
    PREP: Establish signal handlers for SIGSEGV
    PREP: Open a file and initialize it
    PREP: Now set proper permissions and re-open file
    TEST: mmap() with MAP_SHARED returns the address
    where object is mapped
    ERROR: Call to mmap() failed.
    3 FAIL

    Review Information

    Review Type TSMA Review
    Start Date null
    Completed null
    Status Complete
    Review Recommendation No Resolution Given
    Review Response
    This issue comes down to whether or not the specification
    intended to mandate an environment that supports self modifying
    code.

    The quoted opinion above states our objection to this request.

    We remember helping LISP vendors try to debug data/instruction
    cache coherency problems in a PROT_ALL MAP_SHARED environment.
    This plus the fact that other implementations pass the test as it
    is currently written indicates there are implementations that
    intend support for self modifying code.

    LISP vendors are aware that switching data memory to executable
    memory and back again is an alternative to a MAP_SHARED PROT_ALL
    environment. We have been told they consider this less
    efficient, much slower and more difficult to implement than
    a MAP_SHARED PROT_ALL environment.

    We recommend this request be refused.

    Review Type SA Review
    Start Date null
    Completed null
    Status Complete
    Review Resolution Test Suite Deficiency (TSD)
    Review Conclusion
    This is an agreed Test Suite Deficiency. The test suite is assuming more
    than is in the text of the specification.

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