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Re: [Qemu-devel] [6510] Partialy fix mmap at EOF for large pagesize targ
From: |
Lionel Landwerlin |
Subject: |
Re: [Qemu-devel] [6510] Partialy fix mmap at EOF for large pagesize targets in user-mode. |
Date: |
Wed, 04 Feb 2009 21:17:44 +0100 |
Le mardi 03 février 2009 à 23:06 +0000, Edgar E. Iglesias a écrit :
> Revision: 6510
> http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=6510
> Author: edgar_igl
> Date: 2009-02-03 23:06:34 +0000 (Tue, 03 Feb 2009)
>
> Log Message:
> -----------
> Partialy fix mmap at EOF for large pagesize targets in user-mode.
>
> Signed-off-by: Edgar E. Iglesias <address@hidden>
>
> Modified Paths:
> --------------
> trunk/linux-user/mmap.c
>
> Modified: trunk/linux-user/mmap.c
> ===================================================================
> --- trunk/linux-user/mmap.c 2009-02-03 22:45:00 UTC (rev 6509)
> +++ trunk/linux-user/mmap.c 2009-02-03 23:06:34 UTC (rev 6510)
> @@ -24,6 +24,8 @@
> #include <string.h>
> #include <unistd.h>
> #include <errno.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> #include <sys/mman.h>
> #include <linux/mman.h>
> #include <linux/unistd.h>
> @@ -366,6 +368,36 @@
> goto the_end;
> real_start = start & qemu_host_page_mask;
>
> + /* 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 = (sb.st_size - offset);
> + len += qemu_real_host_page_size - 1;
> + len &= ~(qemu_real_host_page_size - 1);
> + }
> + }
> +
> if (!(flags & MAP_FIXED)) {
> abi_ulong mmap_start;
> void *p;
> @@ -381,13 +413,16 @@
> especially important if qemu_host_page_size >
> qemu_real_host_page_size */
> p = mmap(g2h(mmap_start),
> - host_len, prot, flags | MAP_FIXED, fd, host_offset);
> + 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))
> + if (!(flags & MAP_ANONYMOUS)) {
> + p = mmap(g2h(mmap_start), len, prot,
> + flags | MAP_FIXED, fd, host_offset);
> host_start += offset - host_offset;
> + }
> start = h2g(host_start);
> } else {
> int flg;
>
We also need to check when mmap_start pointer is inside the code
generation buffer.
--
Lione Landwerlin
O p e n W i d e 14, rue Gaillon 75002 Paris