POSIX compliance issue with mmap(2)

Garrett Cooper yanegomi at gmail.com
Thu Jul 29 06:47:04 UTC 2010

    According to the page noted below [1], mmap(2) should fail if the
value isn't page-aligned:

    The addr argument (if MAP_FIXED was specified) or off is not a
multiple of the page size as returned by sysconf(), or is considered
invalid by the implementation.

    The current code in vm/vm_mmap.c only applies the check if
MAP_FIXED is specified in flags:

         * Check for illegal addresses.  Watch out for address wrap... Note
         * that VM_*_ADDRESS are not constants due to casts (argh).
        if (flags & MAP_FIXED) {
                 * The specified address must have the same remainder
                 * as the file offset taken modulo PAGE_SIZE, so it
                 * should be aligned after adjustment by pageoff.
                addr -= pageoff;
                if (addr & PAGE_MASK)
                        return (EINVAL);

    Our manpage states this requirement, but doesn't conform to the
POSIX requirements.
    I verified this claim with the failing test [2] by changing
MAP_SHARED to MAP_FIXED. The former case failed, while the latter case

[1] http://www.opengroup.org/onlinepubs/000095399/functions/mmap.html
[2] http://ltp.git.sourceforge.net/git/gitweb.cgi?p=ltp/ltp-dev.git;a=blob;f=testcases/open_posix_testsuite/conformance/interfaces/mmap/11-1.c;h=ed184a17591f0dbb5611ab70218a763a8a66b2df;hb=HEAD

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