Tribblix: manual page: mprotect.2

MPROTECT(2) System Calls MPROTECT(2)

NAME

mprotect - set protection of memory mapping

SYNOPSIS

#include <sys/mman.h>

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

DESCRIPTION

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(3C), to
be that specified by prot. Legitimate values for prot are the same as
those permitted for mmap(2) and are defined in <sys/mman.h> as:

PROT_READ
/* page can be read */

PROT_WRITE
/* page can be written */

PROT_EXEC
/* page can be executed */

PROT_NONE
/* page can not be accessed */

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.

RETURN VALUES

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

ERRORS

The mprotect() function will fail if:

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

EINVAL
The len argument has a value equal to 0, or addr is not a
multiple of the page size as returned by sysconf(3C).

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.

The mprotect() function may fail if:

EAGAIN
The address range [addr, addr + len) includes one or more
pages that have been locked in memory and that were mapped
MAP_PRIVATE; prot includes PROT_WRITE; and the system has
insufficient resources to reserve memory for the private
pages that may be created. These private pages may be
created by store operations in the now-writable address
range.