aboutsummaryrefslogtreecommitdiff
path: root/linux-user/mmap.c
blob: c4371d943a85664f2f450c9d4ac72d93e2157cff (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
/*
 *  mmap support for qemu
 *
 *  Copyright (c) 2003 Fabrice Bellard
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, see <http://www.gnu.org/licenses/>.
 */
#include "qemu/osdep.h"
#include <linux/mman.h>
#include <linux/unistd.h>

#include "qemu.h"
#include "qemu-common.h"
#include "translate-all.h"

//#define DEBUG_MMAP

static pthread_mutex_t mmap_mutex = PTHREAD_MUTEX_INITIALIZER;
static __thread int mmap_lock_count;

void mmap_lock(void)
{
    if (mmap_lock_count++ == 0) {
        pthread_mutex_lock(&mmap_mutex);
    }
}

void mmap_unlock(void)
{
    if (--mmap_lock_count == 0) {
        pthread_mutex_unlock(&mmap_mutex);
    }
}

/* Grab lock to make sure things are in a consistent state after fork().  */
void mmap_fork_start(void)
{
    if (mmap_lock_count)
        abort();
    pthread_mutex_lock(&mmap_mutex);
}

void mmap_fork_end(int child)
{
    if (child)
        pthread_mutex_init(&mmap_mutex, NULL);
    else
        pthread_mutex_unlock(&mmap_mutex);
}

/* NOTE: all the constants are the HOST ones, but addresses are target. */
int target_mprotect(abi_ulong start, abi_ulong len, int prot)
{
    abi_ulong end, host_start, host_end, addr;
    int prot1, ret;

#ifdef DEBUG_MMAP
    printf("mprotect: start=0x" TARGET_ABI_FMT_lx
           "len=0x" TARGET_ABI_FMT_lx " prot=%c%c%c\n", start, len,
           prot & PROT_READ ? 'r' : '-',
           prot & PROT_WRITE ? 'w' : '-',
           prot & PROT_EXEC ? 'x' : '-');
#endif

    if ((start & ~TARGET_PAGE_MASK) != 0)
        return -EINVAL;
    len = TARGET_PAGE_ALIGN(len);
    end = start + len;
    if (end < start)
        return -EINVAL;
    prot &= PROT_READ | PROT_WRITE | PROT_EXEC;
    if (len == 0)
        return 0;

    mmap_lock();
    host_start = start & qemu_host_page_mask;
    host_end = HOST_PAGE_ALIGN(end);
    if (start > host_start) {
        /* handle host page containing start */
        prot1 = prot;
        for(addr = host_start; addr < start; addr += TARGET_PAGE_SIZE) {
            prot1 |= page_get_flags(addr);
        }
        if (host_end == host_start + qemu_host_page_size) {
            for(addr = end; addr < host_end; addr += TARGET_PAGE_SIZE) {
                prot1 |= page_get_flags(addr);
            }
            end = host_end;
        }
        ret = mprotect(g2h(host_start), qemu_host_page_size, prot1 & PAGE_BITS);
        if (ret != 0)
            goto error;
        host_start += qemu_host_page_size;
    }
    if (end < host_end) {
        prot1 = prot;
        for(addr = end; addr < host_end; addr += TARGET_PAGE_SIZE) {
            prot1 |= page_get_flags(addr);
        }
        ret = mprotect(g2h(host_end - qemu_host_page_size), qemu_host_page_size,
                       prot1 & PAGE_BITS);
        if (ret != 0)
            goto error;
        host_end -= qemu_host_page_size;
    }

    /* handle the pages in the middle */
    if (host_start < host_end) {
        ret = mprotect(g2h(host_start), host_end - host_start, prot);
        if (ret != 0)
            goto error;
    }
    page_set_flags(start, start + len, prot | PAGE_VALID);
    mmap_unlock();
    return 0;
error:
    mmap_unlock();
    return ret;
}

/* map an incomplete host page */
static int mmap_frag(abi_ulong real_start,
                     abi_ulong start, abi_ulong end,
                     int prot, int flags, int fd, abi_ulong offset)
{
    abi_ulong real_end, addr;
    void *host_start;
    int prot1, prot_new;

    real_end = real_start + qemu_host_page_size;
    host_start = g2h(real_start);

    /* get the protection of the target pages outside the mapping */
    prot1 = 0;
    for(addr = real_start; addr < real_end; addr++) {
        if (addr < start || addr >= end)
            prot1 |= page_get_flags(addr);
    }

    if (prot1 == 0) {
        /* no page was there, so we allocate one */
        void *p = mmap(host_start, qemu_host_page_size, prot,
                       flags | MAP_ANONYMOUS, -1, 0);
        if (p == MAP_FAILED)
            return -1;
        prot1 = prot;
    }
    prot1 &= PAGE_BITS;

    prot_new = prot | prot1;
    if (!(flags & MAP_ANONYMOUS)) {
        /* msync() won't work here, so we return an error if write is
           possible while it is a shared mapping */
        if ((flags & MAP_TYPE) == MAP_SHARED &&
            (prot & PROT_WRITE))
            return -1;

        /* adjust protection to be able to read */
        if (!(prot1 & PROT_WRITE))
            mprotect(host_start, qemu_host_page_size, prot1 | PROT_WRITE);

        /* read the corresponding file data */
        if (pread(fd, g2h(start), end - start, offset) == -1)
            return -1;

        /* put final protection */
        if (prot_new != (prot1 | PROT_WRITE))
            mprotect(host_start, qemu_host_page_size, prot_new);
    } else {
        if (prot_new != prot1) {
            mprotect(host_start, qemu_host_page_size, prot_new);
        }
        if (prot_new & PROT_WRITE) {
            memset(g2h(start), 0, end - start);
        }
    }
    return 0;
}

#if HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 64
# define TASK_UNMAPPED_BASE  (1ul << 38)
#elif defined(__CYGWIN__)
/* Cygwin doesn't have a whole lot of address space.  */
# define TASK_UNMAPPED_BASE  0x18000000
#else
# define TASK_UNMAPPED_BASE  0x40000000
#endif
abi_ulong mmap_next_start = TASK_UNMAPPED_BASE;

unsigned long last_brk;

/* Subroutine of mmap_find_vma, used when we have pre-allocated a chunk
   of guest address space.  */
static abi_ulong mmap_find_vma_reserved(abi_ulong start, abi_ulong size)
{
    abi_ulong addr;
    abi_ulong end_addr;
    int prot;
    int looped = 0;

    if (size > reserved_va) {
        return (abi_ulong)-1;
    }

    size = HOST_PAGE_ALIGN(size);
    end_addr = start + size;
    if (end_addr > reserved_va) {
        end_addr = reserved_va;
    }
    addr = end_addr - qemu_host_page_size;

    while (1) {
        if (addr > end_addr) {
            if (looped) {
                return (abi_ulong)-1;
            }
            end_addr = reserved_va;
            addr = end_addr - qemu_host_page_size;
            looped = 1;
            continue;
        }
        prot = page_get_flags(addr);
        if (prot) {
            end_addr = addr;
        }
        if (addr + size == end_addr) {
            break;
        }
        addr -= qemu_host_page_size;
    }

    if (start == mmap_next_start) {
        mmap_next_start = addr;
    }

    return addr;
}

/*
 * Find and reserve a free memory area of size 'size'. The search
 * starts at 'start'.
 * It must be called with mmap_lock() held.
 * Return -1 if error.
 */
abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size)
{
    void *ptr, *prev;
    abi_ulong addr;
    int wrapped, repeat;

    /* If 'start' == 0, then a default start address is used. */
    if (start == 0) {
        start = mmap_next_start;
    } else {
        start &= qemu_host_page_mask;
    }

    size = HOST_PAGE_ALIGN(size);

    if (reserved_va) {
        return mmap_find_vma_reserved(start, size);
    }

    addr = start;
    wrapped = repeat = 0;
    prev = 0;

    for (;; prev = ptr) {
        /*
         * Reserve needed memory area to avoid a race.
         * It should be discarded using:
         *  - mmap() with MAP_FIXED flag
         *  - mremap() with MREMAP_FIXED flag
         *  - shmat() with SHM_REMAP flag
         */
        ptr = mmap(g2h(addr), size, PROT_NONE,
                   MAP_ANONYMOUS|MAP_PRIVATE|MAP_NORESERVE, -1, 0);

        /* ENOMEM, if host address space has no memory */
        if (ptr == MAP_FAILED) {
            return (abi_ulong)-1;
        }

        /* Count the number of sequential returns of the same address.
           This is used to modify the search algorithm below.  */
        repeat = (ptr == prev ? repeat + 1 : 0);

        if (h2g_valid(ptr + size - 1)) {
            addr = h2g(ptr);

            if ((addr & ~TARGET_PAGE_MASK) == 0) {
                /* Success.  */
                if (start == mmap_next_start && addr >= TASK_UNMAPPED_BASE) {
                    mmap_next_start = addr + size;
                }
                return addr;
            }

            /* The address is not properly aligned for the target.  */
            switch (repeat) {
            case 0:
                /* Assume the result that the kernel gave us is the
                   first with enough free space, so start again at the
                   next higher target page.  */
                addr = TARGET_PAGE_ALIGN(addr);
                break;
            case 1:
                /* Sometimes the kernel decides to perform the allocation
                   at the top end of memory instead.  */
                addr &= TARGET_PAGE_MASK;
                break;
            case 2:
                /* Start over at low memory.  */
                addr = 0;
                break;
            default:
                /* Fail.  This unaligned block must the last.  */
                addr = -1;
                break;
            }
        } else {
            /* Since the result the kernel gave didn't fit, start
               again at low memory.  If any repetition, fail.  */
            addr = (repeat ? -1 : 0);
        }

        /* Unmap and try again.  */
        munmap(ptr, size);

        /* ENOMEM if we checked the whole of the target address space.  */
        if (addr == (abi_ulong)-1) {
            return (abi_ulong)-1;
        } else if (addr == 0) {
            if (wrapped) {
                return (abi_ulong)-1;
            }
            wrapped = 1;
            /* Don't actually use 0 when wrapping, instead indicate
               that we'd truly like an allocation in low memory.  */
            addr = (mmap_min_addr > TARGET_PAGE_SIZE
                     ? TARGET_PAGE_ALIGN(mmap_min_addr)
                     : TARGET_PAGE_SIZE);
        } else if (wrapped && addr >= start) {
            return (abi_ulong)-1;
        }
    }
}

/* NOTE: all the constants are the HOST ones */
abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
                     int flags, int fd, abi_ulong offset)
{
    abi_ulong ret, end, real_start, real_end, retaddr, host_offset, host_len;

    mmap_lock();
#ifdef DEBUG_MMAP
    {
        printf("mmap: start=0x" TARGET_ABI_FMT_lx
               " len=0x" TARGET_ABI_FMT_lx " prot=%c%c%c flags=",
               start, len,
               prot & PROT_READ ? 'r' : '-',
               prot & PROT_WRITE ? 'w' : '-',
               prot & PROT_EXEC ? 'x' : '-');
        if (flags & MAP_FIXED)
            printf("MAP_FIXED ");
        if (flags & MAP_ANONYMOUS)
            printf("MAP_ANON ");
        switch(flags & MAP_TYPE) {
        case MAP_PRIVATE:
            printf("MAP_PRIVATE ");
            break;
        case MAP_SHARED:
            printf("MAP_SHARED ");
            break;
        default:
            printf("[MAP_TYPE=0x%x] ", flags & MAP_TYPE);
            break;
        }
        printf("fd=%d offset=" TARGET_ABI_FMT_lx "\n", fd, offset);
    }
#endif

    if (offset & ~TARGET_PAGE_MASK) {
        errno = EINVAL;
        goto fail;
    }

    len = TARGET_PAGE_ALIGN(len);
    if (len == 0)
        goto the_end;
    real_start = start & qemu_host_page_mask;
    host_offset = offset & qemu_host_page_mask;

    /* If the user is asking for the kernel to find a location, do that
       before we truncate the length for mapping files below.  */
    if (!(flags & MAP_FIXED)) {
        host_len = len + offset - host_offset;
        host_len = HOST_PAGE_ALIGN(host_len);
        start = mmap_find_vma(real_start, host_len);
        if (start == (abi_ulong)-1) {
            errno = ENOMEM;
            goto fail;
        }
    }

    /* When mapping files into a memory area larger than the file, accesses
       to pages beyond the file size will cause a SIGBUS. 

       For example, if mmaping a file of 100 bytes on a host with 4K pages
       emulating a target with 8K pages, the target expects to be able to
       access the first 8K. But the host will trap us on any access beyond
       4K.  

       When emulating a target with a larger page-size than the hosts, we
       may need to truncate file maps at EOF and add extra anonymous pages
       up to the targets page boundary.  */

    if ((qemu_real_host_page_size < TARGET_PAGE_SIZE)
        && !(flags & MAP_ANONYMOUS)) {
       struct stat sb;

       if (fstat (fd, &sb) == -1)
           goto fail;

       /* Are we trying to create a map beyond EOF?.  */
       if (offset + len > sb.st_size) {
           /* If so, truncate the file map at eof aligned with 
              the hosts real pagesize. Additional anonymous maps
              will be created beyond EOF.  */
           len = REAL_HOST_PAGE_ALIGN(sb.st_size - offset);
       }
    }

    if (!(flags & MAP_FIXED)) {
        unsigned long host_start;
        void *p;

        host_len = len + offset - host_offset;
        host_len = HOST_PAGE_ALIGN(host_len);

        /* Note: we prefer to control the mapping address. It is
           especially important if qemu_host_page_size >
           qemu_real_host_page_size */
        p = mmap(g2h(start), host_len, prot,
                 flags | MAP_FIXED | MAP_ANONYMOUS, -1, 0);
        if (p == MAP_FAILED)
            goto fail;
        /* update start so that it points to the file position at 'offset' */
        host_start = (unsigned long)p;
        if (!(flags & MAP_ANONYMOUS)) {
            p = mmap(g2h(start), len, prot,
                     flags | MAP_FIXED, fd, host_offset);
            if (p == MAP_FAILED) {
                munmap(g2h(start), host_len);
                goto fail;
            }
            host_start += offset - host_offset;
        }
        start = h2g(host_start);
    } else {
        if (start & ~TARGET_PAGE_MASK) {
            errno = EINVAL;
            goto fail;
        }
        end = start + len;
        real_end = HOST_PAGE_ALIGN(end);

	/*
	 * Test if requested memory area fits target address space
	 * It can fail only on 64-bit host with 32-bit target.
	 * On any other target/host host mmap() handles this error correctly.
	 */
        if ((unsigned long)start + len - 1 > (abi_ulong) -1) {
            errno = EINVAL;
            goto fail;
        }

        /* worst case: we cannot map the file because the offset is not
           aligned, so we read it */
        if (!(flags & MAP_ANONYMOUS) &&
            (offset & ~qemu_host_page_mask) != (start & ~qemu_host_page_mask)) {
            /* msync() won't work here, so we return an error if write is
               possible while it is a shared mapping */
            if ((flags & MAP_TYPE) == MAP_SHARED &&
                (prot & PROT_WRITE)) {
                errno = EINVAL;
                goto fail;
            }
            retaddr = target_mmap(start, len, prot | PROT_WRITE,
                                  MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS,
                                  -1, 0);
            if (retaddr == -1)
                goto fail;
            if (pread(fd, g2h(start), len, offset) == -1)
                goto fail;
            if (!(prot & PROT_WRITE)) {
                ret = target_mprotect(start, len, prot);
                assert(ret == 0);
            }
            goto the_end;
        }
        
        /* handle the start of the mapping */
        if (start > real_start) {
            if (real_end == real_start + qemu_host_page_size) {
                /* one single host page */
                ret = mmap_frag(real_start, start, end,
                                prot, flags, fd, offset);
                if (ret == -1)
                    goto fail;
                goto the_end1;
            }
            ret = mmap_frag(real_start, start, real_start + qemu_host_page_size,
                            prot, flags, fd, offset);
            if (ret == -1)
                goto fail;
            real_start += qemu_host_page_size;
        }
        /* handle the end of the mapping */
        if (end < real_end) {
            ret = mmap_frag(real_end - qemu_host_page_size,
                            real_end - qemu_host_page_size, end,
                            prot, flags, fd,
                            offset + real_end - qemu_host_page_size - start);
            if (ret == -1)
                goto fail;
            real_end -= qemu_host_page_size;
        }

        /* map the middle (easier) */
        if (real_start < real_end) {
            void *p;
            unsigned long offset1;
            if (flags & MAP_ANONYMOUS)
                offset1 = 0;
            else
                offset1 = offset + real_start - start;
            p = mmap(g2h(real_start), real_end - real_start,
                     prot, flags, fd, offset1);
            if (p == MAP_FAILED)
                goto fail;
        }
    }
 the_end1:
    page_set_flags(start, start + len, prot | PAGE_VALID);
 the_end:
#ifdef DEBUG_MMAP
    printf("ret=0x" TARGET_ABI_FMT_lx "\n", start);
    page_dump(stdout);
    printf("\n");
#endif
    tb_invalidate_phys_range(start, start + len);
    mmap_unlock();
    return start;
fail:
    mmap_unlock();
    return -1;
}

static void mmap_reserve(abi_ulong start, abi_ulong size)
{
    abi_ulong real_start;
    abi_ulong real_end;
    abi_ulong addr;
    abi_ulong end;
    int prot;

    real_start = start & qemu_host_page_mask;
    real_end = HOST_PAGE_ALIGN(start + size);
    end = start + size;
    if (start > real_start) {
        /* handle host page containing start */
        prot = 0;
        for (addr = real_start; addr < start; addr += TARGET_PAGE_SIZE) {
            prot |= page_get_flags(addr);
        }
        if (real_end == real_start + qemu_host_page_size) {
            for (addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
                prot |= page_get_flags(addr);
            }
            end = real_end;
        }
        if (prot != 0)
            real_start += qemu_host_page_size;
    }
    if (end < real_end) {
        prot = 0;
        for (addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
            prot |= page_get_flags(addr);
        }
        if (prot != 0)
            real_end -= qemu_host_page_size;
    }
    if (real_start != real_end) {
        mmap(g2h(real_start), real_end - real_start, PROT_NONE,
                 MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE,
                 -1, 0);
    }
}

int target_munmap(abi_ulong start, abi_ulong len)
{
    abi_ulong end, real_start, real_end, addr;
    int prot, ret;

#ifdef DEBUG_MMAP
    printf("munmap: start=0x" TARGET_ABI_FMT_lx " len=0x"
           TARGET_ABI_FMT_lx "\n",
           start, len);
#endif
    if (start & ~TARGET_PAGE_MASK)
        return -EINVAL;
    len = TARGET_PAGE_ALIGN(len);
    if (len == 0)
        return -EINVAL;
    mmap_lock();
    end = start + len;
    real_start = start & qemu_host_page_mask;
    real_end = HOST_PAGE_ALIGN(end);

    if (start > real_start) {
        /* handle host page containing start */
        prot = 0;
        for(addr = real_start; addr < start; addr += TARGET_PAGE_SIZE) {
            prot |= page_get_flags(addr);
        }
        if (real_end == real_start + qemu_host_page_size) {
            for(addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
                prot |= page_get_flags(addr);
            }
            end = real_end;
        }
        if (prot != 0)
            real_start += qemu_host_page_size;
    }
    if (end < real_end) {
        prot = 0;
        for(addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
            prot |= page_get_flags(addr);
        }
        if (prot != 0)
            real_end -= qemu_host_page_size;
    }

    ret = 0;
    /* unmap what we can */
    if (real_start < real_end) {
        if (reserved_va) {
            mmap_reserve(real_start, real_end - real_start);
        } else {
            ret = munmap(g2h(real_start), real_end - real_start);
        }
    }

    if (ret == 0) {
        page_set_flags(start, start + len, 0);
        tb_invalidate_phys_range(start, start + len);
    }
    mmap_unlock();
    return ret;
}

abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
                       abi_ulong new_size, unsigned long flags,
                       abi_ulong new_addr)
{
    int prot;
    void *host_addr;

    mmap_lock();

    if (flags & MREMAP_FIXED) {
        host_addr = (void *) syscall(__NR_mremap, g2h(old_addr),
                                     old_size, new_size,
                                     flags,
                                     g2h(new_addr));

        if (reserved_va && host_addr != MAP_FAILED) {
            /* If new and old addresses overlap then the above mremap will
               already have failed with EINVAL.  */
            mmap_reserve(old_addr, old_size);
        }
    } else if (flags & MREMAP_MAYMOVE) {
        abi_ulong mmap_start;

        mmap_start = mmap_find_vma(0, new_size);

        if (mmap_start == -1) {
            errno = ENOMEM;
            host_addr = MAP_FAILED;
        } else {
            host_addr = (void *) syscall(__NR_mremap, g2h(old_addr),
                                         old_size, new_size,
                                         flags | MREMAP_FIXED,
                                         g2h(mmap_start));
            if (reserved_va) {
                mmap_reserve(old_addr, old_size);
            }
        }
    } else {
        int prot = 0;
        if (reserved_va && old_size < new_size) {
            abi_ulong addr;
            for (addr = old_addr + old_size;
                 addr < old_addr + new_size;
                 addr++) {
                prot |= page_get_flags(addr);
            }
        }
        if (prot == 0) {
            host_addr = mremap(g2h(old_addr), old_size, new_size, flags);
            if (host_addr != MAP_FAILED && reserved_va && old_size > new_size) {
                mmap_reserve(old_addr + old_size, new_size - old_size);
            }
        } else {
            errno = ENOMEM;
            host_addr = MAP_FAILED;
        }
        /* Check if address fits target address space */
        if ((unsigned long)host_addr + new_size > (abi_ulong)-1) {
            /* Revert mremap() changes */
            host_addr = mremap(g2h(old_addr), new_size, old_size, flags);
            errno = ENOMEM;
            host_addr = MAP_FAILED;
        }
    }

    if (host_addr == MAP_FAILED) {
        new_addr = -1;
    } else {
        new_addr = h2g(host_addr);
        prot = page_get_flags(old_addr);
        page_set_flags(old_addr, old_addr + old_size, 0);
        page_set_flags(new_addr, new_addr + new_size, prot | PAGE_VALID);
    }
    tb_invalidate_phys_range(new_addr, new_addr + new_size);
    mmap_unlock();
    return new_addr;
}

int target_msync(abi_ulong start, abi_ulong len, int flags)
{
    abi_ulong end;

    if (start & ~TARGET_PAGE_MASK)
        return -EINVAL;
    len = TARGET_PAGE_ALIGN(len);
    end = start + len;
    if (end < start)
        return -EINVAL;
    if (end == start)
        return 0;

    start &= qemu_host_page_mask;
    return msync(g2h(start), end - start, flags);
}