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Problem Report 1612 Details

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Report 1612 Actions

    Problem Report Number 1612
    Submitter's Classification Specification problem
    State Resolved
    Resolution Permanent Interpretation (PIN)
    Problem Resolution ID PIN.X.0169
    Raised 1996-08-09 08:00
    Updated 2003-03-13 08:00
    Published 1996-09-11 08:00
    Product Standard Internationalised System Calls and Libraries Extended (UNIX 95)
    Certification Program The Open Brand certification program
    Test Suite VSU version 4.1.0
    Test Identification CAPI.hdr/misc/time-sys 29 31 33
    Specification System Interfaces and Libraries Issue 4 Version 2
    Location in Spec See Problem Text
    Problem Summary PIN4U.00035 This test may fail on implementations which evaluate the first argument to FD_SET, FD_CLR, or FD_ISSET more than once.
    Problem Text
    In our implementation, the first arguments of the macros FD_SET, FD_CLR,
    and FD_ISSET in <sys/time.h> are each evaluated more than once. XPG4,
    Version 2 specification while not explicitly disallowing this, references
    the ISO C standard which makes the following statement in section titled
    "Use of Library Functions":

    Any invocation of a library function that is implemented as
    a macro shall expand to code that evaluates each of its arguments
    exactly once, fully protected by parentheses where necessary, so it
    is generally safe to use arbitrary expressions as arguments.

    The tests are testing this requirement. The problem is that historically,
    these have been implemented as macros and these macros have always
    evaluated the first arguments more than once. Note that though the C
    standard makes a requirement with respect to argument evaluation for
    macros, there are exceptions within the C standard itself. The following
    statement is taken from the description for the putc function:

    The putc function is equivalent to fputc except that if it
    is implemented as a macro, it may evaluate stream more than
    once...

    A similar statement exists for the getc function.

    Although the description for select() states that it is unspecified whether
    or not FD_CLR, FD_ISSET, FD_SET, or FD_ZERO are implemented
    as macros or functions, the description for <sys/time.h> states that each
    of these be defined as macros. Given historical practice and the fact
    that the C standard has made exceptions with regard to the evaluation of
    macro arguments, we believe that an exception is warranted in this case as
    well.
    Test Output
    TEST CASE: sys/time.h

    TEST PURPOSE #29
    If the macro void FD_SET(int fd, fd_set *fdset) is
    defined in sys/time.h it shall evaluate each of its
    arguments exactly once, fully protected by parentheses
    where necessary, and return void.
    TEST: Argument evaluation
    ERROR: Argument 1 of FD_SET evaluated 2 times
    29 FAIL

    TEST PURPOSE #31
    If the macro void FD_CLR(int fd, fd_set *fdset) is
    defined in sys/time.h it shall evaluate each of its
    arguments exactly once, fully protected by parentheses
    where necessary, and return void.
    TEST: Argument evaluation
    ERROR: Argument 1 of FD_CLR evaluated 2 times
    31 FAIL

    TEST PURPOSE #33
    If the macro int FD_ISSET(int fd, fd_set *fdset) is
    defined in sys/time.h it shall evaluate each of its
    arguments exactly once, fully protected by parentheses
    where necessary, and return a value of the correct type.
    TEST: Argument evaluation
    ERROR: Argument 1 of FD_ISSET evaluated 2 times
    TEST: Return protection
    TEST: Return type
    33 FAIL

    Review Information

    Review Type TSMA Review
    Start Date null
    Completed null
    Status Complete
    Review Recommendation No Resolution Given
    Review Response
    We recommend this request be refused.

    PG4U.00032 and 1170 base resolution #33 have already addressed this issue.

    BR# 1170/33 states

    REQUEST:

    Traditional implementations of the FD_SET, FD_CLR, FD_ISSET
    macros evaluate their first argument more than once.

    In the absence of further information from the specification the
    test suite assumes that the macros should only evaluate their
    arguments once and flag existing inplementations as being
    non-compliant.

    We belive the specification should be changed to allow existing
    practice.

    X/OPEN RESOLUTION:

    If macro versions of these functions are provided they must
    evaluate their arguments only once. This is an ISO C
    requirement.

    The only additional information this request adds is that the C
    spec allows putc and getc to scan their second arguments more
    than once. We do not believe this adds any weight to the submitter's
    argument. The XSH spec also specifically allows these functions to
    scan these arguments more than once, but makes no such allowance
    for any arguments to the FD_* macros.

    Review Type SA Review
    Start Date null
    Completed null
    Status Complete
    Review Resolution No Resolution Given
    Review Conclusion
    Traditionally these functions have been provided as macros only with
    no underlying functions. A waiver is grantd to permit traditional behaviour.

    Review Type SA Review
    Start Date null
    Completed null
    Status Complete
    Review Resolution Permanent Interpretation (PIN)
    Review Conclusion
    A Permanent Interpretation is granted.

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