mprotect(2)                                                        mprotect(2)



NAME
     mprotect - set protection of memory mapping

SYNOPSIS
     #include <sys/types.h>
     #include <sys/mman.h>

     int mprotect(void *addr, sizet len, int prot);


DESCRIPTION

     The function mprotect changes the access protections on the mappings

     specified by the range [addr, addr + len) to be that specified by prot.

     Legitimate values for prot are the same as those permitted for mmap and

     are defined in <sys/mman.h> as:


     PROTREAD       /* page can be read */

     PROTWRITE      /* page can be written */

     PROTEXEC       /* page can be executed */

     PROTNONE       /* page can not be accessed */


     Not all implementations literally provide all possible combinations.

     PROTWRITE is often implemented as PROTREAD|PROTWRITE and PROTEXEC as

     PROTREAD|PROTEXEC.  This is true for all SGI implementations.  In

     particular, MIPS processors do not support a separate execute permission.

     Any page that can be read can be executed from, even if PROTEXEC is not

     specified.  As described below, the operating system uses PROTEXEC as a

     flag to indicate it may need to perform certain platform dependent

     functions that may be needed to properly execute instructions from the

     associated page.  However, no implementation will permit a store to

     succeed where PROTWRITE has not been set.


     Applications such as compiling interpreters that generate code in their

     data areas and then wish to execute it, should use mprotect to add

     PROTEXEC permission to the corresponding pages.  This must be done after

     the code has been generated, but before it is executed.  This causes any

     necessary machine dependent activities, such as cache flushing, to occur

     that are required prior to executing from any part of the process's

     address space other than the program or library text segments.  If the

     generated instructions are altered after the previous call to mprotect

     was made to mark the data as executable, then mprotect must be called to

     again add PROTEXEC before the new code is executed in order to prepare

     the new contents of the page(s) for proper execution.


RETURN VALUE

     On success, mprotect returns 0; on failure, mprotect returns -1 and sets

     errno to indicate an error.


ERRORS

     Under the following conditions, the function mprotect fails and sets

     errno to:






                                                                        Page 1

mprotect(2)                                                        mprotect(2)



     EACCES prot specifies a protection that violates the access permission
            the process has to the underlying memory object.

     EAGAIN prot specifies PROTWRITE over a MAPPRIVATE mapping and there are
            insufficient memory resources to reserve for locking the private
            page.

     EINVAL addr is not a multiple of the page size as returned by sysconf.

     ENOMEM The argument len has a value less than or equal to 0.

     ENOMEM Addresses in the range [addr, addr + len) are invalid for the
            address space of a process, or specify one or more pages which are
            not mapped.

     When mprotect fails for reasons other than EINVAL, the protections on
     some of the pages in the range [addr, addr + len) may have been changed.
     If the error occurs on some page at addr2, then the protections of all
     whole pages in the range [addr, addr2] will have been modified.

SEE ALSO
     mmap(2), plock(2), sysconf(3C)

































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