memctl(2)                      DG/UX R4.11MU05                     memctl(2)


NAME
       memctl - set memory access for mapping

SYNOPSIS
       #include <sys/m88kbcs.h>

       int memctl(addr, len, state)
       caddrt *addr;
       int     len;
       int     state;

DESCRIPTION
       The DG/UX system provides alternative calls for setting memory
       access: memctl(2), defined by the 88open Binary Compatibility
       Standard (BCS), revision 1.1A; and mprotect(2), defined by the System
       V Interface Definition, Issue 3 (SVID3). If your program must be BCS-
       compliant, use memctl(2) as explained below. Otherwise, use
       mprotect(2).

       The memctl(2) call sets access attributes for a designated region of
       memory:

       addr  is the starting address of the memory region.

       len   is the length in bytes of the region.

       state is the access attribute: MCT_RONLY for read access, MCT_DATA
             for read-write access, MCT_TEXT for read-execute access, or
             MCT_RWX for read-write-execute access.

             Note: MCT_RWX is supported on the DG/UX system but not on all
             BCS-compliant platforms. Use sysconf(2) with the
             _SC_RWX_SUPPORT parameter to find out whether it is supported.

       The addr and len must be integer multiples of the memory control
       unit. Use sysconf(2) with the _SC_MEMCTL_UNIT parameter to find out
       the size of this unit.  Also, the memory region specified by addr and
       len must all be mapped within the caller's address space.

       Programs that modify and execute a memory region, and which will run
       on a BCS-compliant platform that supports simultaneous read-write-
       execute access, should do the following:

       ·    Set the access state of the region to MCT_RWX.

       ·    After the  modification and prior to execution, notify the
            system to allow for synchronization of hardware cache and memory
            contents. Use a trap to vector 502 for the notification, as
            explained in the 88open Binary Compatibility Standard (BCS),
            revision 1.1A, chapter 9. (When several processes share a memory
            region, at least one of them performs notification for the
            others, following all modifications and preceding execution by
            any of them.)

       Programs that modify and execute a memory region, and which will run
       on a platform that does not support MCT_RWX, should use memctl(2) to
       flip between read-write and read-execute access.  Namely:

       ·    After a write operation, before attempting an execute operation,
            set the access state of the region to read-execute (MCT_TEXT).

       ·    After an execute operation, before attempting a write operation,
            set the region's access state to read-write (MCT_DATA).

ACCESS CONTROL
       In the following two cases, the state must be either read-only
       (MCTRONLY) or read-write (MCTTEXT):

       ·    One or more pages in the region lie in a shared memory segment
            that was attached using the SHMRDONLY option.

       ·    One or more pages in the region have been mapped using mmap(2)
            with the MAPSHARED option, and the file passed to mmap(2) was
            not open for writing.  (If your program maps with mmap(2), it
            should, for consistency, use the ABI-compliant mprotect and/or
            csync calls instead of the BCS-compliant memctl call.)

RETURN VALUE
       Upon successful completion, memctl(2) returns 0. Otherwise, it
       returns -1 and sets errno to indicate the error.

DIAGNOSTICS
       If memctl(2) fails, it sets errno to one of the following:

       EACCES         A mapping within the memory region lacks the required
                      permission to change its memory to the requested
                      state.

       EAGAIN         The access state is MCT_DATA or MCT_RWX; the memory
                      needed to lock one or more private pages in the region
                      is unavailable.

       EAGAIN         The access state is MCT_DATA or MCT_RWX; the swap
                      space needed to modify one or more private pages in
                      the region is unavailable.

       EFAULT         The memory region is not fully mapped in the caller's
                      address space.

       EINVAL         The state parameter is invalid.

       EINVAL         The addr address parameter is not aligned on a memory
                      control unit boundary.

       EINVAL         The len parameter is not an integral multiple of the
                      memory control unit for the system.

SEE ALSO
       mmap(2), mprotect(2), shmat(2), stkexec(2), sysconf(2).


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