234 lines
5.8 KiB
Groff
234 lines
5.8 KiB
Groff
.\" $NetBSD: mremap.2,v 1.7 2018/05/03 05:09:48 wiz Exp $
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.\"
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.\" Copyright (c) 2007 Thomas Klausner and Joerg Sonnenberger
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" ------------------------------------------------------------
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.Dd May 2, 2018
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.Dt MREMAP 2
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.Os
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.Sh NAME
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.Nm mremap
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.Nd re-map a virtual memory address
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.\" ------------------------------------------------------------
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/mman.h
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.Ft void *
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.Fn mremap "void *oldp" "size_t oldsize" "void *newp" "size_t newsize" \
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"int flags"
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.\" ------------------------------------------------------------
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.Sh DESCRIPTION
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The
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.Fn mremap
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function resizes the mapped range (see
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.Xr mmap 2 )
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starting at
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.Ar oldp
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and having size
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.Ar oldsize
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to
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.Ar newsize .
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The following arguments can be
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.Dv OR Ap ed
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together in the
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.Ar flags
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argument:
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.Bl -tag -width XXMAPXALIGNEDXnXX
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.It Dv MAP_ALIGNED Ns Pq Ar n
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The allocation should be aligned to the given boundary, i.e. ensure
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that the lowest
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.Ar n
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bits of the address are zero.
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The parameter
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.Ar n
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should be the base 2 logarithm of the desired alignment (e.g., to
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request alignment to 16K, use 14 as the value for n).
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The alignment must be equal to or greater than the platform's page
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size as returned by
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.Xr sysconf 3
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with the
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.Dv _SC_PAGESIZE
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request.
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.It Dv MAP_FIXED
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.Ar newp
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is tried and
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.Fn mremap
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fails if that address can't be used as new base address for the range.
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Otherwise,
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.Ar oldp
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and
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.Ar newp
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are used as hints for the position, factoring in the given alignment.
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.It Dv MAP_REMAPDUP
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Duplicate the mapping.
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Both address ranges reference the same pages, but can have different protection flags.
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.El
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.Sh RETURN VALUES
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.Fn mremap
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returns the new address or
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.Dv MAP_FAILED ,
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if the remap failed.
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.Sh EXAMPLES
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The following example program creates a two mappings for the same
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memory range, one RW- and one R-X.
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.Bd -literal
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#include <sys/types.h>
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#include <sys/mman.h>
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#include <stdio.h>
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#include <string.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <err.h>
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static int
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return_1(void)
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{
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return 1;
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}
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static void
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return_1_end(void)
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{
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}
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static int
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return_2(void)
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{
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return 2;
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}
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static void
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return_2_end(void)
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{
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}
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int
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main(int argc, char *argv[])
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{
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void *maprw, *maprx;
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int rv;
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size_t page = (size_t)sysconf(_SC_PAGESIZE);
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// Create the first mapping that has no protections, but intended
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// protections only
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maprw = mmap(NULL, page,
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PROT_MPROTECT(PROT_EXEC|PROT_WRITE|PROT_READ),
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MAP_ANON, -1, 0);
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if (maprw == MAP_FAILED)
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err(EXIT_FAILURE, "mmap failed");
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// Create the second mapping for the same physical space, which
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// again has no protections.
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maprx = mremap(maprw, page, NULL, page, MAP_REMAPDUP);
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if (maprx == MAP_FAILED)
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err(EXIT_FAILURE, "mremap failed");
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// Set the first mapping read/write
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if (mprotect(maprw, page, PROT_READ|PROT_WRITE) == -1)
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err(EXIT_FAILURE, "mprotect(rw) failed");
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// Set the second mapping read/execute
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if (mprotect(maprx, page, PROT_READ|PROT_EXEC) == -1)
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err(EXIT_FAILURE, "mprotect(rx) failed");
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#define XS(a) (size_t)((uintptr_t)(a ## _end) - (uintptr_t)(a))
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// Copy and run the first function
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memcpy(maprw, return_1, XS(return_1));
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__builtin___clear_cache(maprw, (void *)((uintptr_t)maprw + page));
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rv = ((int (*)(void))maprx)();
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printf("%d\en", rv);
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// Copy and run the second function
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memcpy(maprw, return_2, XS(return_2));
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__builtin___clear_cache(maprw, (void *)((uintptr_t)maprw + page));
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rv = ((int (*)(void))maprx)();
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printf("%d\en", rv);
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return EXIT_SUCCESS;
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}
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.Ed
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.Sh COMPATIBILITY
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The semantics of
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.Fn mremap
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differ from the one provided by glibc on Linux in that the
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.Ar newp
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argument was added and a different set of
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.Ar flags
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are implemented.
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.Sh ERRORS
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The
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.Fn mremap
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function fails if:
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.Bl -tag -width Er
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.It Bq Er E2BIG
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A request to extend
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.Fa oldp
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failed because of address overflow.
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.It Bq Er EINVAL
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If
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.Fa oldp
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or
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.Fa newp
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are not page aligned, or
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.Fa oldsize
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or
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.Fa newsize
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are not a multiple of the page size, or if
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.Fa oldp +
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.Fa oldsize
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or
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.Fa newp +
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.Fa newsize
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wrap around, or if an invalid alignment was requested in the
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.Fa flags
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argument, or if the request was to extend
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.Fa oldp
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and the extension address space either did not fit, was already occupied,
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or had set permissions.
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.It Bq Er ENOENT
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If the
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.Fa oldp
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segmented was not already mapped.
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.It Bq Er ENOMEM
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If there was either no space to allocate/move memory,
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or if a fixed allocation was requested in the
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.Fa flags
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that could not be accommodated.
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.El
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.Sh SEE ALSO
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.Xr mmap 2 ,
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.Xr munmap 2
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.Sh HISTORY
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The
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.Fn mremap
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system call appeared in
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.Nx 5.0 .
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It was based on the code that supports
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.Fn mremap
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compatibility for Linux binaries.
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