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* mmap support for qemu
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* Copyright (c) 2003 - 2008 Fabrice Bellard
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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#include "qemu-common.h"
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#if defined(CONFIG_USE_NPTL)
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pthread_mutex_t mmap_mutex;
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static int __thread mmap_lock_count;
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if (mmap_lock_count++ == 0) {
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pthread_mutex_lock(&mmap_mutex);
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void mmap_unlock(void)
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if (--mmap_lock_count == 0) {
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pthread_mutex_unlock(&mmap_mutex);
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/* Grab lock to make sure things are in a consistent state after fork(). */
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void mmap_fork_start(void)
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pthread_mutex_lock(&mmap_mutex);
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void mmap_fork_end(int child)
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pthread_mutex_init(&mmap_mutex, NULL);
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pthread_mutex_unlock(&mmap_mutex);
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/* We aren't threadsafe to start with, so no need to worry about locking. */
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void mmap_unlock(void)
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void *qemu_vmalloc(size_t size)
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/* Use map and mark the pages as used. */
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p = mmap(NULL, size, PROT_READ | PROT_WRITE,
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MAP_PRIVATE | MAP_ANON, -1, 0);
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/* Allocated region overlaps guest address space.
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abi_ulong addr = h2g(p);
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page_set_flags(addr & TARGET_PAGE_MASK, TARGET_PAGE_ALIGN(addr + size),
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void *qemu_malloc(size_t size)
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p = qemu_vmalloc(size);
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/* We use map, which is always zero initialized. */
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void * qemu_mallocz(size_t size)
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return qemu_malloc(size);
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void qemu_free(void *ptr)
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/* FIXME: We should unmark the reserved pages here. However this gets
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complicated when one target page spans multiple host pages, so we
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p = (size_t *)((char *)ptr - 16);
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void *qemu_realloc(void *ptr, size_t size)
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size_t old_size, copy;
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return qemu_malloc(size);
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old_size = *(size_t *)((char *)ptr - 16);
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copy = old_size < size ? old_size : size;
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new_ptr = qemu_malloc(size);
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memcpy(new_ptr, ptr, copy);
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/* NOTE: all the constants are the HOST ones, but addresses are target. */
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int target_mprotect(abi_ulong start, abi_ulong len, int prot)
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abi_ulong end, host_start, host_end, addr;
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printf("mprotect: start=0x" TARGET_FMT_lx
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" len=0x" TARGET_FMT_lx " prot=%c%c%c\n", start, len,
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prot & PROT_READ ? 'r' : '-',
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prot & PROT_WRITE ? 'w' : '-',
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prot & PROT_EXEC ? 'x' : '-');
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if ((start & ~TARGET_PAGE_MASK) != 0)
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len = TARGET_PAGE_ALIGN(len);
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prot &= PROT_READ | PROT_WRITE | PROT_EXEC;
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host_start = start & qemu_host_page_mask;
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host_end = HOST_PAGE_ALIGN(end);
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if (start > host_start) {
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/* handle host page containing start */
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for(addr = host_start; addr < start; addr += TARGET_PAGE_SIZE) {
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prot1 |= page_get_flags(addr);
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if (host_end == host_start + qemu_host_page_size) {
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for(addr = end; addr < host_end; addr += TARGET_PAGE_SIZE) {
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prot1 |= page_get_flags(addr);
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ret = mprotect(g2h(host_start), qemu_host_page_size, prot1 & PAGE_BITS);
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host_start += qemu_host_page_size;
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if (end < host_end) {
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for(addr = end; addr < host_end; addr += TARGET_PAGE_SIZE) {
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prot1 |= page_get_flags(addr);
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ret = mprotect(g2h(host_end - qemu_host_page_size), qemu_host_page_size,
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host_end -= qemu_host_page_size;
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/* handle the pages in the middle */
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if (host_start < host_end) {
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ret = mprotect(g2h(host_start), host_end - host_start, prot);
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page_set_flags(start, start + len, prot | PAGE_VALID);
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/* map an incomplete host page */
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static int mmap_frag(abi_ulong real_start,
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abi_ulong start, abi_ulong end,
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int prot, int flags, int fd, abi_ulong offset)
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abi_ulong real_end, addr;
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real_end = real_start + qemu_host_page_size;
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host_start = g2h(real_start);
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/* get the protection of the target pages outside the mapping */
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for(addr = real_start; addr < real_end; addr++) {
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if (addr < start || addr >= end)
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prot1 |= page_get_flags(addr);
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/* no page was there, so we allocate one */
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void *p = mmap(host_start, qemu_host_page_size, prot,
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flags | MAP_ANON, -1, 0);
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prot_new = prot | prot1;
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if (!(flags & MAP_ANON)) {
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/* msync() won't work here, so we return an error if write is
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possible while it is a shared mapping */
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if ((flags & TARGET_BSD_MAP_FLAGMASK) == MAP_SHARED &&
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/* adjust protection to be able to read */
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if (!(prot1 & PROT_WRITE))
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mprotect(host_start, qemu_host_page_size, prot1 | PROT_WRITE);
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/* read the corresponding file data */
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pread(fd, g2h(start), end - start, offset);
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/* put final protection */
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if (prot_new != (prot1 | PROT_WRITE))
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mprotect(host_start, qemu_host_page_size, prot_new);
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/* just update the protection */
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if (prot_new != prot1) {
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mprotect(host_start, qemu_host_page_size, prot_new);
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#if defined(__CYGWIN__)
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/* Cygwin doesn't have a whole lot of address space. */
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static abi_ulong mmap_next_start = 0x18000000;
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static abi_ulong mmap_next_start = 0x40000000;
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unsigned long last_brk;
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/* find a free memory area of size 'size'. The search starts at
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'start'. If 'start' == 0, then a default start address is used.
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/* page_init() marks pages used by the host as reserved to be sure not
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static abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size)
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abi_ulong addr, addr1, addr_start;
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unsigned long new_brk;
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new_brk = (unsigned long)sbrk(0);
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if (last_brk && last_brk < new_brk && last_brk == (target_ulong)last_brk) {
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/* This is a hack to catch the host allocating memory with brk().
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If it uses mmap then we loose.
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FIXME: We really want to avoid the host allocating memory in
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the first place, and maybe leave some slack to avoid switching
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page_set_flags(last_brk & TARGET_PAGE_MASK,
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TARGET_PAGE_ALIGN(new_brk),
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size = HOST_PAGE_ALIGN(size);
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start = start & qemu_host_page_mask;
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addr = mmap_next_start;
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for(addr1 = addr; addr1 < (addr + size); addr1 += TARGET_PAGE_SIZE) {
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prot |= page_get_flags(addr1);
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addr += qemu_host_page_size;
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/* we found nothing */
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if (addr == addr_start)
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return (abi_ulong)-1;
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mmap_next_start = addr + size;
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/* NOTE: all the constants are the HOST ones */
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abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
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int flags, int fd, abi_ulong offset)
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abi_ulong ret, end, real_start, real_end, retaddr, host_offset, host_len;
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unsigned long host_start;
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printf("mmap: start=0x" TARGET_FMT_lx
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" len=0x" TARGET_FMT_lx " prot=%c%c%c flags=",
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prot & PROT_READ ? 'r' : '-',
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prot & PROT_WRITE ? 'w' : '-',
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prot & PROT_EXEC ? 'x' : '-');
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if (flags & MAP_FIXED)
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printf("MAP_FIXED ");
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if (flags & MAP_ANON)
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switch(flags & TARGET_BSD_MAP_FLAGMASK) {
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printf("MAP_PRIVATE ");
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printf("MAP_SHARED ");
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printf("[MAP_FLAGMASK=0x%x] ", flags & TARGET_BSD_MAP_FLAGMASK);
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printf("fd=%d offset=" TARGET_FMT_lx "\n", fd, offset);
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if (offset & ~TARGET_PAGE_MASK) {
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len = TARGET_PAGE_ALIGN(len);
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real_start = start & qemu_host_page_mask;
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if (!(flags & MAP_FIXED)) {
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abi_ulong mmap_start;
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host_offset = offset & qemu_host_page_mask;
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host_len = len + offset - host_offset;
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host_len = HOST_PAGE_ALIGN(host_len);
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mmap_start = mmap_find_vma(real_start, host_len);
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if (mmap_start == (abi_ulong)-1) {
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/* Note: we prefer to control the mapping address. It is
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especially important if qemu_host_page_size >
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qemu_real_host_page_size */
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p = mmap(g2h(mmap_start),
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host_len, prot, flags | MAP_FIXED, fd, host_offset);
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/* update start so that it points to the file position at 'offset' */
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host_start = (unsigned long)p;
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if (!(flags & MAP_ANON))
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host_start += offset - host_offset;
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start = h2g(host_start);
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if (start & ~TARGET_PAGE_MASK) {
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real_end = HOST_PAGE_ALIGN(end);
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for(addr = real_start; addr < real_end; addr += TARGET_PAGE_SIZE) {
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flg = page_get_flags(addr);
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if (flg & PAGE_RESERVED) {
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/* worst case: we cannot map the file because the offset is not
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aligned, so we read it */
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if (!(flags & MAP_ANON) &&
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(offset & ~qemu_host_page_mask) != (start & ~qemu_host_page_mask)) {
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/* msync() won't work here, so we return an error if write is
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possible while it is a shared mapping */
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if ((flags & TARGET_BSD_MAP_FLAGMASK) == MAP_SHARED &&
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(prot & PROT_WRITE)) {
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retaddr = target_mmap(start, len, prot | PROT_WRITE,
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MAP_FIXED | MAP_PRIVATE | MAP_ANON,
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pread(fd, g2h(start), len, offset);
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if (!(prot & PROT_WRITE)) {
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ret = target_mprotect(start, len, prot);
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/* handle the start of the mapping */
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if (start > real_start) {
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if (real_end == real_start + qemu_host_page_size) {
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/* one single host page */
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ret = mmap_frag(real_start, start, end,
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prot, flags, fd, offset);
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ret = mmap_frag(real_start, start, real_start + qemu_host_page_size,
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prot, flags, fd, offset);
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real_start += qemu_host_page_size;
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/* handle the end of the mapping */
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if (end < real_end) {
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ret = mmap_frag(real_end - qemu_host_page_size,
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real_end - qemu_host_page_size, real_end,
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offset + real_end - qemu_host_page_size - start);
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real_end -= qemu_host_page_size;
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/* map the middle (easier) */
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if (real_start < real_end) {
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unsigned long offset1;
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if (flags & MAP_ANON)
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offset1 = offset + real_start - start;
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p = mmap(g2h(real_start), real_end - real_start,
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prot, flags, fd, offset1);
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page_set_flags(start, start + len, prot | PAGE_VALID);
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printf("ret=0x" TARGET_FMT_lx "\n", start);
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int target_munmap(abi_ulong start, abi_ulong len)
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abi_ulong end, real_start, real_end, addr;
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printf("munmap: start=0x%lx len=0x%lx\n", start, len);
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if (start & ~TARGET_PAGE_MASK)
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len = TARGET_PAGE_ALIGN(len);
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real_start = start & qemu_host_page_mask;
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real_end = HOST_PAGE_ALIGN(end);
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if (start > real_start) {
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/* handle host page containing start */
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for(addr = real_start; addr < start; addr += TARGET_PAGE_SIZE) {
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prot |= page_get_flags(addr);
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if (real_end == real_start + qemu_host_page_size) {
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for(addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
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prot |= page_get_flags(addr);
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real_start += qemu_host_page_size;
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if (end < real_end) {
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for(addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
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prot |= page_get_flags(addr);
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real_end -= qemu_host_page_size;
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/* unmap what we can */
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if (real_start < real_end) {
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ret = munmap(g2h(real_start), real_end - real_start);
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page_set_flags(start, start + len, 0);
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int target_msync(abi_ulong start, abi_ulong len, int flags)
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if (start & ~TARGET_PAGE_MASK)
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len = TARGET_PAGE_ALIGN(len);
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start &= qemu_host_page_mask;
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return msync(g2h(start), end - start, flags);