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HP-UX 11i Version 3: February 2007

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mprotect() — set or check protection of memory mapping


#include <sys/mman.h> int mprotect(void *addr, size_t len, int prot);


The mprotect() function changes the access protections on the mappings specified by the range [addr, addr+len], rounding len up to the next multiple of the page size as returned by sysconf(), 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>:


Page can be read.


Page can be written.


Page can be executed.


Page cannot be accessed.


Check page effective permissions

If PROT_CHECK flag is specified, mprotect() checks the access protections on the mappings specified with the rest of prot value to see if the requested permissions are set.

If the address range being modified corresponds to a mapped file that was mapped with MAP_SHARED, mprotect() grants write access permission only if the file descriptor used to map the file was opened for writing. If the address range corresponds to a mapped file that was mapped with the MAP_PRIVATE or the MAP_ANONYMOUS flag, mprotect() grants all requested access permissions.

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.

For example, if an error occurs on some page at an addr2, then mprotect() may have modified the protections of all whole pages in the range [addr,addr2].


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


The mprotect() function will fail if:


The prot argument specifies a protection that violates, or is different than (in the case where flag PROT_CHECK is present), the access permission the process has to the underlying memory object.


prot is invalid, or addr is not a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE).


The range specified by [addr, addr+len] (from, and including, addr to, but not including, addr+len) is invalid for the address space of a process, or the range specifies one or more unmapped pages.


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.


The prot argument specifies PROT_WRITE over a MAP_PRIVATE mapping and there are insufficient memory resources to reserve for locking the private page.


mprotect() was developed by HP, AT&T, and OSF.


mmap(2), sysconf(2), <sys/mman.h>.


mprotect(): AES, SVID3

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